From: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx> If CONFIG_DEBUG_INFO_DWARF* is enabled, the compiler generates DWARF Call Frame Information (CFI) for every object file and places it in a special section named ".debug_frame". The CFI information can be used for frame pointer validation. Implement a CFI parser in objtool. This can be invoked as follows: objtool dwarf generate <object-file> The version of the DWARF standard supported in this work is version 4. The official documentation for this version is here: https://dwarfstd.org/doc/DWARF4.pdf Section 6.4 contains the description of the CFI. Initial implementation ====================== This initial work is for supporting frame pointer validation for ARM64. That said, it is generic enough to support other architectures in the future. CFI defines 7 different register rules to compute register values at every instruction address. These are described below. Of these, only the first 3 rules are generated by gcc and clang for the stack pointer (SP), the frame pointer (FP) and the return address (RA) for ARM64. As of this writing, the same is true for RISCV as well. So, in objtool, provide support for the first three rules and mark the rest as unsupported. Register rules ============== CFI defines the Canonical Frame Address (CFA) as the value of the SP when a call instruction is executed. For the called function, other register values are expressed relative to the CFA. CFI defines the following rules to obtain the value of a register in the previous frame, given a current frame: 1. Same_Value: The current and previous values of the register are the same. 2. Val_Offset(N): The previous value is (CFA + N) where N is a signed offset. 3. Offset(N): The previous value is saved at (CFA + N). 4. register(R): The previous value is saved in register R. 5. Val_Expression(E): The previous value is the value produced by evaluating a given DWARF expression. DWARF expressions are evaluated on a stack. That is, operands are pushed and popped on a stack, DWARF operators are applied on them and the result is obtained. 6. Expression(E): The previous value is stored at the address computed from a DWARF expression. 7. Architectural: The previous value is obtained in an architecture-specific way via an architecture-specific "augmentor". Augmentors are vendor specific and are not part of the DWARF standard. DWARF rule encoding =================== The CFI is defined in a very generic format to allow all of the above rules to be defined for different architectures. Since this work uses only a minimal subset of the rules, the supported CFI rules can be encoded in a more compact format for the kernel. Provide stubs for generating compact rule data from the CFI rules. In a future patch, the stubs will be filled with actual code and the rules will be written to a special section in the object file. And, in a future patch, the kernel will use the rule data. Unsupported rules ================= For arm64, this is not an issue. If the compiler generates unsupported rules for the SP, FP and RA for some other architecture, objtool will not generate any rule data for those code locations. These will be treated as unreliable PCs from an unwinder perspective. FP prolog, epilog and leaf functions ==================================== This implementation recognizes these cases in the DWARF CFI. It does not generate any rule data unless the frame is completely setup. So, if an interrupt or an exception were to happen in the prolog, epilog or a function where the frame has not been set up for whatever reason, the kernel will recognize that and consider the code unreliable from an unwinder perspective. Assembly functions ================== DWARF CFI is generated by the compiler only for C functions. So, objtool will not generate any rule data for assembly functions. By default, the kernel will consider all assembly functions as unreliable from an unwinder perspective. DWARF annotations for assembly code can be used so CFI can be generated for assembly functions as well. However, DWARF annotations are a pain to maintain. So, we should never go down that path. Now, there are certain points in assembly code that we would like to unwind through reliably. Like interrupt and exception handlers. For these, unwind hints can be defined and placed at strategic points in assembly code. This will be done in a futurep patch. Unwind hints are a lot simpler and a lot easier to maintain than DWARF annotations. Generated code ============== Generated code will not have any DWARF rules. The kernel will consider such code unreliable from an unwinder perspective. Architecture-specific part =========================== The following pieces in this implementation are architecture-specific. Code must be provided for each architecture spearately. - DWARF register number to architecture register mapping - Relocation handling for rule data (relocation types are processor-specific) - ABI-specific checking of rules parsed by objtool. Only a small amount of architecture-specific code is required. Other aspects such as endianness and address size are handled in the generic code. Signed-off-by: Madhavan T. Venkataraman <madvenka@xxxxxxxxxxxxxxxxxxx> --- tools/objtool/Build | 5 + tools/objtool/Makefile | 10 +- tools/objtool/arch/arm64/Build | 2 + tools/objtool/arch/arm64/dwarf_arch.c | 114 ++++ tools/objtool/arch/arm64/dwarf_clang.c | 53 ++ .../arch/arm64/include/arch/dwarf_reg.h | 17 + tools/objtool/builtin-dwarf.c | 57 ++ tools/objtool/dwarf_op.c | 560 ++++++++++++++++++ tools/objtool/dwarf_parse.c | 294 +++++++++ tools/objtool/dwarf_rules.c | 37 ++ tools/objtool/dwarf_util.c | 280 +++++++++ tools/objtool/elf.c | 2 +- tools/objtool/include/objtool/builtin.h | 1 + tools/objtool/include/objtool/dwarf_def.h | 438 ++++++++++++++ tools/objtool/include/objtool/elf.h | 1 + tools/objtool/include/objtool/objtool.h | 1 + tools/objtool/objtool.c | 1 + tools/objtool/weak.c | 27 + 18 files changed, 1898 insertions(+), 2 deletions(-) create mode 100644 tools/objtool/arch/arm64/Build create mode 100644 tools/objtool/arch/arm64/dwarf_arch.c create mode 100644 tools/objtool/arch/arm64/dwarf_clang.c create mode 100644 tools/objtool/arch/arm64/include/arch/dwarf_reg.h create mode 100644 tools/objtool/builtin-dwarf.c create mode 100644 tools/objtool/dwarf_op.c create mode 100644 tools/objtool/dwarf_parse.c create mode 100644 tools/objtool/dwarf_rules.c create mode 100644 tools/objtool/dwarf_util.c create mode 100644 tools/objtool/include/objtool/dwarf_def.h diff --git a/tools/objtool/Build b/tools/objtool/Build index b7222d5cc7bc..2ab5885398c1 100644 --- a/tools/objtool/Build +++ b/tools/objtool/Build @@ -7,9 +7,14 @@ objtool-$(SUBCMD_CHECK) += special.o objtool-$(SUBCMD_ORC) += check.o objtool-$(SUBCMD_ORC) += orc_gen.o objtool-$(SUBCMD_ORC) += orc_dump.o +objtool-$(SUBCMD_DWARF) += dwarf_parse.o +objtool-$(SUBCMD_DWARF) += dwarf_op.o +objtool-$(SUBCMD_DWARF) += dwarf_rules.o +objtool-$(SUBCMD_DWARF) += dwarf_util.o objtool-y += builtin-check.o objtool-y += builtin-orc.o +objtool-y += builtin-dwarf.o objtool-y += elf.o objtool-y += objtool.o diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile index 92ce4fce7bc7..2bc84ac5515f 100644 --- a/tools/objtool/Makefile +++ b/tools/objtool/Makefile @@ -41,13 +41,21 @@ AWK = awk SUBCMD_CHECK := n SUBCMD_ORC := n +SUBCMD_DWARF := n ifeq ($(SRCARCH),x86) SUBCMD_CHECK := y SUBCMD_ORC := y endif -export SUBCMD_CHECK SUBCMD_ORC +ifeq ($(SRCARCH),arm64) + SUBCMD_DWARF := y +ifneq ($(LLVM),) + SUBCMD_DWARF_CLANG := y +endif +endif + +export SUBCMD_CHECK SUBCMD_ORC SUBCMD_DWARF SUBCMD_DWARF_CLANG export srctree OUTPUT CFLAGS SRCARCH AWK include $(srctree)/tools/build/Makefile.include diff --git a/tools/objtool/arch/arm64/Build b/tools/objtool/arch/arm64/Build new file mode 100644 index 000000000000..e5710de8060f --- /dev/null +++ b/tools/objtool/arch/arm64/Build @@ -0,0 +1,2 @@ +objtool-$(SUBCMD_DWARF) += dwarf_arch.o +objtool-$(SUBCMD_DWARF_CLANG) += dwarf_clang.o diff --git a/tools/objtool/arch/arm64/dwarf_arch.c b/tools/objtool/arch/arm64/dwarf_arch.c new file mode 100644 index 000000000000..2607ec94a12e --- /dev/null +++ b/tools/objtool/arch/arm64/dwarf_arch.c @@ -0,0 +1,114 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * dwarf_arch.c - Architecture-specific support functions. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ +#include <stdio.h> +#include <errno.h> + +#include <objtool/objtool.h> +#include <objtool/warn.h> +#include <objtool/dwarf_def.h> +#include <arch/dwarf_reg.h> +#include <linux/kconfig.h> +#include <linux/compiler.h> + +int arch_dwarf_fde_reloc(struct fde *fde) +{ + GElf_Rela rela; + struct symbol *rela_symbol; + int index; + + /* + * Find the code section, offset within the section and the symbol of + * the function for this FDE. We need the symbol for debugging purposes. + * We need the section and offset to set up relocation for the DWARF + * rules that we will create in a separate section. + */ + if (debug_frame->reloc) { + /* + * In this case, debug frame entries are relocatable. For every + * FDE, there is a pair of relocation entries - one for the FDE + * itself and one for the function it represents. So, we use + * the second entry in each pair to find the section, section + * offset and the symbol for the function. + */ + index = (fde->index * 2) + 1; + if (!gelf_getrela(debug_frame->reloc->data, index, &rela)) { + WARN_ELF("gelf_getrela"); + return -ENOENT; + } + rela_symbol = find_symbol_by_index(dwarf_file->elf, + GELF_R_SYM(rela.r_info)); + fde->section = find_section_by_name(dwarf_file->elf, + rela_symbol->name); + if (!fde->section) { + WARN("No section for FDE"); + return -ENOENT; + } + fde->offset = rela.r_addend; + fde->symbol = find_symbol_containing(fde->section, fde->offset); + } else { + /* + * In this case, the debug frame entries are not relocatable. + * In the normal build of the kernel, this code is not required + * because objtool will be run on relocatable objects. But + * this code can handle it if objtool is run on the vmlinux + * binary itself. This is for debugging purposes. + */ + struct section *sec; + GElf_Shdr *sh; + unsigned long addr = fde->start_pc; + unsigned long start_addr, end_addr; + + fde->section = NULL; + for_each_sec(dwarf_file, sec) { + sh = &sec->sh; + start_addr = sh->sh_addr; + end_addr = start_addr + sh->sh_size; + if (addr >= start_addr && addr < end_addr) { + fde->section = sec; + break; + } + } + if (!fde->section) { + WARN("No section for FDE"); + return -ENOENT; + } + fde->offset = 0; + fde->symbol = find_symbol_containing(fde->section, + fde->start_pc); + } + fde->start_pc += fde->offset; + fde->end_pc += fde->offset; + return 0; +} + +/* + * If the offsets are 0, it means that the frame is not fully set up at + * this point in the object code. E.g., in the frame pointer prolog or epilog + * or in a leaf function. Check for this. + * + * If the frame is properly set up, then the frame pointer and return + * address are saved adjacent to each other. Check for this. + */ +int arch_dwarf_check_rules(struct fde *fde, unsigned long pc, + struct rule *sp_rule, struct rule *fp_rule, + struct rule *ra_rule) +{ + if (!sp_rule->offset || sp_rule->saved || + !fp_rule->offset || !fp_rule->saved) + return -EINVAL; + + if (!ra_rule->offset || !ra_rule->saved || + (fp_rule->offset + 8) != ra_rule->offset) + return -EINVAL; + + if (fde) + arch_dwarf_clang_hack(fde, pc, sp_rule, fp_rule); + + return 0; +} diff --git a/tools/objtool/arch/arm64/dwarf_clang.c b/tools/objtool/arch/arm64/dwarf_clang.c new file mode 100644 index 000000000000..e07ccf9484cf --- /dev/null +++ b/tools/objtool/arch/arm64/dwarf_clang.c @@ -0,0 +1,53 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * dwarf_arch.c - Architecture-specific support functions. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ +#include <stdio.h> +#include <errno.h> + +#include <objtool/objtool.h> +#include <objtool/warn.h> +#include <objtool/dwarf_def.h> +#include <arch/dwarf_reg.h> +#include <linux/kconfig.h> +#include <linux/compiler.h> + +void arch_dwarf_clang_hack(struct fde *fde, unsigned long pc, + struct rule *sp_rule, struct rule *fp_rule) +{ + struct section *sec = fde->section; + unsigned long start_pc = 0; + unsigned int instruction; + unsigned int opcode, rd, rn, imm; + + if (!fde) + return; + + if (!sec->reloc) + start_pc = sec->sh.sh_addr; + + instruction = *(unsigned int *)(sec->data->d_buf + pc - start_pc - 4); + rd = instruction & 0x1F; + rn = (instruction >> 5) & 0x1F; + imm = (instruction >> 10) & 0x3FFF; + opcode = instruction >> 24; + + if (opcode == 0x91 && rn == SP_REG && rd == FP_REG && imm && + sp_rule->offset == -fp_rule->offset) { + fde->sp_offset = imm; + } + + imm = (instruction >> 10) & 0xFFF; + opcode = instruction >> 22; + + if (opcode == 0x344 && rn == SP_REG && rd == SP_REG && imm && + sp_rule->offset == -fp_rule->offset) { + fde->sp_offset = imm; + } + + sp_rule->offset += fde->sp_offset; +} diff --git a/tools/objtool/arch/arm64/include/arch/dwarf_reg.h b/tools/objtool/arch/arm64/include/arch/dwarf_reg.h new file mode 100644 index 000000000000..b3c61060bb67 --- /dev/null +++ b/tools/objtool/arch/arm64/include/arch/dwarf_reg.h @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * dwarf_reg.h - DWARF register numbers for the stack pointer, frame pointer + * and return address. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (c) 2022 Microsoft Corporation + */ +#ifndef _ARM64_ARCH_DWARF_REG_H +#define _ARM64_ARCH_DWARF_REG_H + +#define FP_REG 29 +#define RA_REG 30 +#define SP_REG 31 + +#endif /* _ARM64_ARCH_DWARF_REG_H */ diff --git a/tools/objtool/builtin-dwarf.c b/tools/objtool/builtin-dwarf.c new file mode 100644 index 000000000000..f44b35eb3f55 --- /dev/null +++ b/tools/objtool/builtin-dwarf.c @@ -0,0 +1,57 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * builtin-dwarf.c - DWARF command invoked by "objtool dwarf ...". + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ + +/* + * objtool dwarf: + * + * This command analyzes a .o file and adds .dwarf_rules and .dwarf_offsets + * sections to it, which is used by the in-kernel reliable unwinder. + */ + +#include <stdio.h> +#include <string.h> +#include <objtool/builtin.h> +#include <objtool/objtool.h> + +static const char * const dwarf_usage[] = { + /* + * Generate DWARF rules for the kernel from DWARF Call Frame + * information. + */ + "objtool dwarf generate file", + + NULL, +}; + +const struct option dwarf_options[] = { + OPT_END(), +}; + +int cmd_dwarf(int argc, const char **argv) +{ + const char *object; + struct objtool_file *file; + + argc--; argv++; + if (argc != 2) + usage_with_options(dwarf_usage, dwarf_options); + + object = argv[1]; + + file = objtool_open_read(object); + if (!file) + return 1; + + if (!strncmp(argv[0], "gen", 3)) + return dwarf_parse(file); + + usage_with_options(dwarf_usage, dwarf_options); + + return 0; +} diff --git a/tools/objtool/dwarf_op.c b/tools/objtool/dwarf_op.c new file mode 100644 index 000000000000..31f9e0b4fd4b --- /dev/null +++ b/tools/objtool/dwarf_op.c @@ -0,0 +1,560 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * dwarf_op.c - Code to parse DWARF operations in object files. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ + +#include <stdio.h> + +#include <objtool/objtool.h> +#include <objtool/warn.h> +#include <objtool/dwarf_def.h> +#include <arch/dwarf_reg.h> +#include <linux/compiler.h> + +unsigned char op, operand; + +static unsigned long cur_address; +static struct rule sp_rule; +static struct rule fp_rule; +static struct rule ra_rule; +static bool unsupported; + +static inline bool dwarf_ignore_reg(unsigned int reg) +{ + /* + * We don't care about registers other than the stack pointer, frame + * pointer and the return address (if defined). + */ + return reg != SP_REG && reg != FP_REG && reg != RA_REG; +} + +static inline void dwarf_offset_rule(unsigned int reg, long offset, bool saved) +{ + if (dwarf_ignore_reg(reg)) + return; + + if (reg == FP_REG && offset > 0) { + /* This is for Clang. */ + reg = SP_REG; + } + + if (reg == SP_REG) { + sp_rule.offset = offset; + sp_rule.saved = saved; + } else if (reg == FP_REG) { + fp_rule.offset = offset; + fp_rule.saved = saved; + } else { + ra_rule.offset = offset; + ra_rule.saved = saved; + } +} + +static inline void dwarf_reg_rule(unsigned int reg, unsigned int other_reg) +{ + if (dwarf_ignore_reg(reg) && dwarf_ignore_reg(other_reg)) + return; + + /* + * We don't support the SP, FP and RA being saved in other registers + * and vice-versa. + */ + WARN("op=%d register rule for %d is not supported", op, reg); + unsupported = true; +} + +static inline void dwarf_restore_rule(unsigned int reg) +{ + if (dwarf_ignore_reg(reg)) + return; + + if (reg == SP_REG) + sp_rule = cur_cie->sp_rule; + else if (reg == FP_REG) + fp_rule = cur_cie->fp_rule; + else + ra_rule = cur_cie->ra_rule; +} + +static inline void dwarf_expression_rule(unsigned int reg) +{ + if (dwarf_ignore_reg(reg)) + return; + + /* + * We don't support expressions to compute the values for the SP, FP + * and RA. + */ + WARN("op=%d is not supported!", op); + unsupported = true; +} + +static inline void dwarf_undefined_rule(unsigned int reg) +{ + if (dwarf_ignore_reg(reg)) + return; + + /* + * We don't support the values for the SP, FP and RA being undefined. + */ + WARN("op=%d %d register undefined?", op, reg); + unsupported = true; +} + +/* + * Whenever the PC is changed, the SP and FP rules for the range (old PC to + * new PC) have to be written out in the form of a DWARF rule before + * changing the PC. + */ +static void dwarf_set_address(unsigned long address, bool *fail) +{ + bool skip = false; + + if (unsupported) { + /* + * We were not able to compute the rules. Reset the rules. + * Do not generate a DWARF rule for this code range. The + * kernel will therefore not be able to find the rules for + * the code range and will consider the range to be unreliable + * from an unwind perspective. + */ + unsupported = false; + dwarf_offset_rule(SP_REG, 0, false); + dwarf_offset_rule(FP_REG, 0, false); + dwarf_offset_rule(RA_REG, 0, false); + skip = true; + } + + if (arch_dwarf_check_rules(cur_fde, cur_address, + &sp_rule, &fp_rule, &ra_rule)) { + /* + * Ignore the rules for now. Do not generate a DWARF rule + * for this code range. The kernel will therefore not be able + * to find the rules for the code range and will consider the + * range to be unreliable from an unwind perspective. We do + * not reset the rules as they can get modified by further + * DWARF instruction processing to the point where they are + * not ignored anymore. + */ + skip = true; + } + + if (skip) + dwarf_rule_next(cur_fde, cur_address); + else if (dwarf_rule_add(cur_fde, cur_address, &sp_rule, &fp_rule)) + *fail = true; + cur_address = address; +} + +static unsigned char *dwarf_one_op(unsigned char *start, unsigned char *end) +{ + unsigned long length; + unsigned char byte; + unsigned int delta; + u64 pc, reg, other_reg; + s64 offset; + bool fail = false; + + byte = *start++; + + /* Primary op code in the high 2 bits */ + op = byte & 0xc0; + operand = byte & 0x3F; + if (op == DW_CFA_extended_op) { + /* Extended op is in the low 6 bits. */ + op = operand; + } + + switch (op) { + /* + * No-op instruction, used for padding. + */ + case DW_CFA_nop: + break; + + /* + * Instructions that advance the current PC. + */ + case DW_CFA_advance_loc: + /* + * The factored delta is the operand itself. Add the delta to + * the current instruction address to obtain the new + * instruction address. + */ + delta = (unsigned int) operand; + delta *= cur_cie->code_factor; + dwarf_set_address(cur_address + delta, &fail); + break; + case DW_CFA_set_loc: + /* + * Extract the target PC. Set the current instruction address + * to it. + */ + if (cur_cie->address_size == 64) + GET_VALUE(pc, start, end, 8); + else + GET_VALUE(pc, start, end, 4); + dwarf_set_address(pc, &fail); + break; + case DW_CFA_advance_loc1: + /* + * Extract the factored delta (unsigned byte) and add it to the + * current instruction address to obtain the new instruction + * address. + */ + GET_VALUE(delta, start, end, 1); + delta *= cur_cie->code_factor; + dwarf_set_address(cur_address + delta, &fail); + break; + case DW_CFA_advance_loc2: + /* + * Extract the factored delta (unsigned short) and add it to + * the current instruction address to obtain the new + * instruction address. + */ + GET_VALUE(delta, start, end, 2); + delta *= cur_cie->code_factor; + dwarf_set_address(cur_address + delta, &fail); + break; + case DW_CFA_advance_loc4: + /* + * Extract the factored delta (unsigned int) and add it to + * the current instruction address to obtain the new + * instruction address. + */ + GET_VALUE(delta, start, end, 4); + delta *= cur_cie->code_factor; + dwarf_set_address(cur_address + delta, &fail); + break; + + /* + * CFA definition instructions. + */ + case DW_CFA_def_cfa: + /* + * Extract the CFA register and the unfactored CFA offset. + * Define a val_offset(N) rule. + */ + READ_ULEB_128(reg, start, end, fail); + READ_ULEB_128(offset, start, end, fail); + cur_cie->cfa_reg = reg; + cur_cie->cfa_offset = offset; + dwarf_offset_rule(cur_cie->cfa_reg, cur_cie->cfa_offset, false); + break; + case DW_CFA_def_cfa_sf: + /* + * Same as DW_CFA_def_cfa except that the offset is signed + * and factored. + */ + READ_ULEB_128(reg, start, end, fail); + READ_SLEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + cur_cie->cfa_reg = reg; + cur_cie->cfa_offset = offset; + dwarf_offset_rule(cur_cie->cfa_reg, cur_cie->cfa_offset, false); + break; + case DW_CFA_def_cfa_register: + /* + * Same as DW_CFA_def_cfa except that the saved offset is used. + */ + READ_ULEB_128(reg, start, end, fail); + cur_cie->cfa_reg = reg; + dwarf_offset_rule(cur_cie->cfa_reg, cur_cie->cfa_offset, false); + break; + case DW_CFA_def_cfa_offset: + /* + * Same as DW_CFA_def_cfa except that the saved register is + * used. + */ + READ_ULEB_128(offset, start, end, fail); + cur_cie->cfa_offset = offset; + dwarf_offset_rule(cur_cie->cfa_reg, cur_cie->cfa_offset, false); + break; + case DW_CFA_def_cfa_offset_sf: + /* + * Same as DW_CFA_def_cfa_offset except that the offset is + * signed and factored. + */ + READ_SLEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + cur_cie->cfa_offset = offset; + dwarf_offset_rule(cur_cie->cfa_reg, cur_cie->cfa_offset, false); + break; + case DW_CFA_def_cfa_expression: + READ_ULEB_128(length, start, end, fail); + /* + * Skip the expression bytes. + */ + start += length; + if (start > end) + fail = true; + dwarf_expression_rule(SP_REG); + break; + + /* + * Register rule instructions. + */ + case DW_CFA_undefined: + READ_ULEB_128(reg, start, end, fail); + dwarf_undefined_rule(reg); + break; + case DW_CFA_same_value: + /* + * Set the register offset to be "same value". That is, it has + * not been modified by the callee. + */ + READ_ULEB_128(reg, start, end, fail); + dwarf_offset_rule(reg, 0, false); + break; + case DW_CFA_offset: + /* + * The register number that is encoded in the operand itself. + * Extract the factored offset. Define an offset(N) rule. + */ + reg = operand; + READ_ULEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + dwarf_offset_rule(reg, offset, true); + break; + case DW_CFA_offset_extended: + /* + * Same as DW_CFA_offset except for the encoding and size of + * the register operand. + */ + READ_ULEB_128(reg, start, end, fail); + READ_ULEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + dwarf_offset_rule(reg, offset, true); + break; + case DW_CFA_offset_extended_sf: + /* + * Same as DW_CFA_offset_extended except that the offset is + * signed and factored. + */ + READ_ULEB_128(reg, start, end, fail); + READ_SLEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + dwarf_offset_rule(reg, offset, true); + break; + case DW_CFA_val_offset: + /* + * Extract the register number and the factored offset. Define + * a val_offset(N) rule. + */ + READ_ULEB_128(reg, start, end, fail); + READ_ULEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + dwarf_offset_rule(reg, offset, false); + break; + case DW_CFA_val_offset_sf: + /* + * Same as DW_CFA_val_offset except that the offset is signed. + */ + READ_ULEB_128(reg, start, end, fail); + READ_SLEB_128(offset, start, end, fail); + offset *= cur_cie->data_factor; + dwarf_offset_rule(reg, offset, false); + break; + case DW_CFA_register: + READ_ULEB_128(reg, start, end, fail); + READ_ULEB_128(other_reg, start, end, fail); + dwarf_reg_rule(reg, other_reg); + break; + case DW_CFA_expression: + case DW_CFA_val_expression: + READ_ULEB_128(reg, start, end, fail); + READ_ULEB_128(length, start, end, fail); + /* + * Skip the expression bytes. + */ + start += length; + if (start > end) + fail = true; + dwarf_expression_rule(reg); + break; + case DW_CFA_restore: + /* + * Restore the rule for the register to the one specified in + * the CIE. + */ + reg = operand; + dwarf_restore_rule(reg); + break; + case DW_CFA_restore_extended: + /* + * Same as DW_CFA_restore except for the encoding and size of + * the register operand. + */ + READ_ULEB_128(reg, start, end, fail); + dwarf_restore_rule(reg); + break; + + /* + * Rule state instructions. + */ + case DW_CFA_remember_state: + cur_cie->saved_sp_rule = sp_rule; + cur_cie->saved_fp_rule = fp_rule; + cur_cie->saved_ra_rule = ra_rule; + break; + case DW_CFA_restore_state: + sp_rule = cur_cie->saved_sp_rule; + fp_rule = cur_cie->saved_fp_rule; + ra_rule = cur_cie->saved_ra_rule; + break; + default: + if (op >= DW_CFA_lo_user && op <= DW_CFA_hi_user) { + /* + * Ignore arch-specific or vendor-specific ops as they + * are irrelevant to the stack and frame pointers. + */ + } else { + WARN("Illegal CFA op %d", (int) op); + fail = true; + } + break; + } + return fail ? NULL : start; +} + +/* + * Run the DWARF instructions in a CIE or an FDE. + */ +static unsigned char *dwarf_op(unsigned char *start, unsigned char *end) +{ + bool fail = false; + + /* cur_fde is set if this is an FDE. */ + if (cur_fde) { + /* + * For an FDE, the rules are initialized from the rules + * computed for its CIE. + */ + sp_rule = cur_cie->sp_rule; + fp_rule = cur_cie->fp_rule; + ra_rule = cur_cie->ra_rule; + } else { + /* + * For a CIE, the rule is initialized to all zeroes. + */ + dwarf_offset_rule(SP_REG, 0, false); + dwarf_offset_rule(FP_REG, 0, false); + dwarf_offset_rule(RA_REG, 0, false); + } + + /* + * If an unsupported DWARF rule is discovered in dwarf_one_op(), + * this will be set to true. + */ + unsupported = false; + + while (start < end) { + start = dwarf_one_op(start, end); + if (!start) + return NULL; + } + + if (cur_fde) { + /* Generate the final rule for the FDE. */ + dwarf_set_address(cur_fde->end_pc, &fail); + } + return start; +} + +/* + * Parse DWARF instructions in CIEs and FDEs. + */ +void dwarf_parse_instructions(void) +{ + struct cie *cie; + struct fde *fde; + unsigned char *start, *end; + + cur_fde = NULL; + + for (cie = cies; cie != NULL; cie = cie->next) { + cur_cie = cie; + start = cie->instructions; + end = start + cie->instructions_size; + + /* + * Run the DWARF instructions in the CIE to compute the + * initial SP, FP and RA rules. + */ + if (!dwarf_op(start, end)) { + cur_cie->unusable = true; + continue; + } + + cie->sp_rule = sp_rule; + cie->fp_rule = fp_rule; + cie->ra_rule = ra_rule; + } + + for (fde = fdes; fde != NULL; fde = fde->next) { + /* + * If any problems are encountered below, simply skip the FDE. + * This means that no DWARF rules from this FDE will be + * included. So, the kernel will consider the FDE's code range + * to be unreliable from an unwinding perspective. + */ + + /* + * Find the CIE for this FDE using the section offset of the + * CIE. The CIE list is already in increasing section offset + * order. + */ + for (cie = cies; cie != NULL; cie = cie->next) { + if (cie->offset < fde->cie_offset) + continue; + if (cie->offset == fde->cie_offset) + fde->cie = cie; + break; + } + + cur_cie = fde->cie; + if (cur_cie == NULL || cur_cie->unusable) { + WARN("No CIE: Could not process FDE"); + continue; + } + + if (!fde->section) { + /* + * The section is needed to create relocation entries + * for the DWARF rules in the FDE. + */ + WARN("No section: Could not process FDE"); + continue; + } + cur_fde = fde; + + /* + * Run the DWARF instructions in the FDE to derive the rules + * for computing the SP and the FP within the FDE code range. + * Encode the rules in the form of DWARF rules for the benefit + * of the kernel. dwarf_op() will generate the rules as it runs + * the instructions. + */ + dwarf_rule_start(fde); + + cur_address = fde->start_pc; + start = fde->instructions; + end = start + fde->instructions_size; + + if (!dwarf_op(start, end)) { + /* + * Rollback the DWARF rules created in the above + * call. + */ + WARN("FDE instructions failed. Rolling back FDE."); + dwarf_rule_reset(fde); + continue; + } + + dwarf_rule_next(fde, fde->end_pc); + } +} diff --git a/tools/objtool/dwarf_parse.c b/tools/objtool/dwarf_parse.c new file mode 100644 index 000000000000..d5ac5630fbba --- /dev/null +++ b/tools/objtool/dwarf_parse.c @@ -0,0 +1,294 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * dwarf_parse.c - Code to parse DWARF information in object files. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ + +#include <stdio.h> +#include <errno.h> + +#include <objtool/objtool.h> +#include <objtool/warn.h> +#include <objtool/dwarf_def.h> +#include <linux/compiler.h> + +struct objtool_file *dwarf_file; +struct section *debug_frame; + +struct cie *cies, *cur_cie; +struct fde *fdes, *cur_fde; + +static struct cie *cies_tail; +static struct fde *fdes_tail; + +static u64 cie_id; +static int fde_index; +static int address_size; +static unsigned int offset_size; +static u64 entry_length; +static unsigned char *saved_start; + +/* + * Parse and create a new CIE. + */ +static unsigned char *dwarf_parse_cie(unsigned char *start, unsigned char *end) +{ + struct cie *cie; + bool fail = false; + + cie = dwarf_alloc(sizeof(*cie)); + if (!cie) { + WARN("%s: dwarf_alloc(cie) failed", __func__); + return NULL; + } + memset(cie, 0, sizeof(*cie)); + + /* Add CIE to global list. */ + if (cies_tail == NULL) + cies = cie; + else + cies_tail->next = cie; + cies_tail = cie; + cie->next = NULL; + + /* Section offset where this CIE resides. */ + cie->offset = saved_start - (unsigned char *) debug_frame->data->d_buf; + cie->length = entry_length; + cie->id = cie_id; + cie->unusable = false; + + /* + * Extract the DWARF CFI version. This is different from the DWARF + * version. + */ + cie->version = *start++; + if (cie->version > 4) { + /* + * This implementation does not support these versions. For + * instance, segment selectors are not supported. + */ + WARN("CIE version %d is not supported", cie->version); + return NULL; + } + + /* + * Store the size of an address in this architecture. + */ + if (cie->version == 4) { + GET_VALUE(cie->address_size, start, end, 1); + GET_VALUE(cie->segment_size, start, end, 1); + cie->address_size += cie->segment_size; + } else { + cie->address_size = address_size; + } + + /* + * This implementation does not support an augmentor. For instance, + * the address_size can be modified by the augmentor. Make sure that + * the augmentor is the null string. + */ + cie->augmentation = (char *) start; + if (*start++ != '\0') { + WARN("Augmentor is not supported"); + return NULL; + } + cie->segment_size = 0; + + /* Extract code alignment factor. */ + READ_ULEB_128(cie->code_factor, start, end, fail); + + /* Extract data alignment factor. */ + READ_SLEB_128(cie->data_factor, start, end, fail); + + if (cie->version == 1) + GET_VALUE(cie->return_address_reg, start, end, 1); + else + READ_ULEB_128(cie->return_address_reg, start, end, fail); + + /* The remaining bytes are DWARF instructions. */ + cie->instructions = start; + cie->instructions_size = end - start; + start = end; + + return fail ? NULL : start; +} + +/* + * Parse and create a new FDE. + */ +static unsigned char *dwarf_parse_fde(unsigned char *start, unsigned char *end) +{ + struct fde *fde; + unsigned long length; + + fde = dwarf_alloc(sizeof(*fde)); + if (!fde) { + WARN("%s: dwarf_alloc(fde) failed", __func__); + return NULL; + } + memset(fde, 0, sizeof(*fde)); + + /* Add FDE to global list. */ + if (fdes_tail == NULL) + fdes = fde; + else + fdes_tail->next = fde; + fdes_tail = fde; + fde->next = NULL; + + /* + * This is the index of the FDE record in the .debug_frame section. + * This is used to locate the symbol for the FDE in a relocatable + * object file. + */ + fde->index = fde_index++; + fde->length = entry_length; + + /* + * For an FDE, the CIE ID field actually contains the section offset + * of the CIE for the FDE. + */ + fde->cie_offset = cie_id; + + /* + * Set the CIE for this FDE to NULL for now. We will set this to the + * correct CIE later. + */ + fde->cie = NULL; + fde->segment_selector = 0; + + /* + * Extract the starting address of the code range to which this FDE + * applies. + */ + GET_VALUE(fde->start_pc, start, end, address_size); + + /* Extract the size of the code range to which this FDE applies. */ + GET_VALUE(length, start, end, address_size); + fde->end_pc = fde->start_pc + length; + + /* The remaining bytes are DWARF instructions. */ + fde->instructions = start; + fde->instructions_size = end - start; + start = end; + + /* Relocation is arch-specific. */ + if (arch_dwarf_fde_reloc(fde) == -EOPNOTSUPP) + return NULL; + + return start; +} + +/* + * Parse one entry for an FDE - either a CIE or an FDE. + */ +static unsigned char *dwarf_parse_one(unsigned char *start, unsigned char *end) +{ + bool is_cie; + + saved_start = start; + + /* + * The first value in an entry is the length field. + */ + GET_VALUE(entry_length, start, end, 4); + if (entry_length == 0) { + WARN("Illegal length in DWARF entry"); + return NULL; + } + + /* + * For 64 bit entries, the first 32 bits of the entry is all 1's. The + * actual length is after that. + */ + if (entry_length == 0xffffffff) { + GET_VALUE(entry_length, start, end, 8); + offset_size = 8; + } else { + offset_size = 4; + } + + if (entry_length > (size_t) (end - start)) { + WARN("DWARF entry is too big"); + return NULL; + } + end = start + entry_length; + + /* + * The CIE identifier field distinguishes between a CIE and an FDE. For + * a CIE, this field contains a specific ID value. For an FDE, it + * contains the section offset of the CIE used by the FDE. + */ + GET_VALUE(cie_id, start, end, offset_size); + + is_cie = (offset_size == 4 && cie_id == CIE_ID_32) || + (offset_size == 8 && cie_id == CIE_ID_64); + if (is_cie) + start = dwarf_parse_cie(start, end); + else + start = dwarf_parse_fde(start, end); + return start; +} + +/* + * Parse DWARF Call Frame Information. + */ +int dwarf_parse(struct objtool_file *file) +{ + unsigned char *start, *end; + + dwarf_file = file; + + /* + * Initialize the helper function based on endianness. This function + * is used to extract values from the DWARF section. + */ + switch (file->elf->ehdr.e_ident[EI_DATA]) { + default: + __fallthrough; + case ELFDATANONE: + __fallthrough; + case ELFDATA2LSB: + get_value = get_value_le; /* Little endian */ + break; + case ELFDATA2MSB: + get_value = get_value_be; /* Big endian */ + break; + } + + if (file->elf->ehdr.e_ident[EI_CLASS] == ELFCLASS64) + address_size = 64; + else + address_size = 32; + + /* + * DWARF Call Frame Information is contained in .debug_frame. + * NOTE: This implementation does not support .eh_frame. + */ + debug_frame = find_section_by_name(file->elf, ".debug_frame"); + if (!debug_frame) + return 0; + + dwarf_alloc_init(); + + /* + * Parse all the entries in .debug_frame and create CIEs and FDEs. + */ + start = debug_frame->data->d_buf; + end = start + debug_frame->data->d_size; + + while (start < end) { + start = dwarf_parse_one(start, end); + if (!start) + return -1; + } + + /* + * Run all the DWARF instructions in the CIEs and FDEs. + */ + dwarf_parse_instructions(); + return 0; +} diff --git a/tools/objtool/dwarf_rules.c b/tools/objtool/dwarf_rules.c new file mode 100644 index 000000000000..9cf201de392a --- /dev/null +++ b/tools/objtool/dwarf_rules.c @@ -0,0 +1,37 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * dwarf_rules.c - Allocation and management of DWARF rules. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ +#include <stdio.h> + +#include <objtool/objtool.h> +#include <objtool/warn.h> +#include <objtool/dwarf_def.h> +#include <linux/compiler.h> + +/* + * The following are stubs for now. Later, they will be filled to create + * DWARF rules that the kernel can use to compute the frame pointer at + * a given instruction address. + */ +void dwarf_rule_start(struct fde *fde) +{ +} + +int dwarf_rule_add(struct fde *fde, unsigned long addr, + struct rule *sp_rule, struct rule *fp_rule) +{ + return 0; +} + +void dwarf_rule_next(struct fde *fde, unsigned long addr) +{ +} + +void dwarf_rule_reset(struct fde *fde) +{ +} diff --git a/tools/objtool/dwarf_util.c b/tools/objtool/dwarf_util.c new file mode 100644 index 000000000000..77c70c54d26f --- /dev/null +++ b/tools/objtool/dwarf_util.c @@ -0,0 +1,280 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * dwarf_util.c - Support functions. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ +#include <stdio.h> +#include <objtool/warn.h> +#include <objtool/dwarf_def.h> +#include <linux/types.h> + +void *free_space; +size_t free_size; + +/* Function to extract embedded values in the DWARF instruction stream. */ +u64 (*get_value)(unsigned char *field, unsigned int size); + +/* + * Little endian helper. Adapted from binutils. + */ +u64 get_value_le(unsigned char *field, unsigned int size) +{ + switch (size) { + case 1: + return *field; + + case 2: + return ((unsigned int) (field[0])) | + (((unsigned int) (field[1])) << 8); + + case 3: + return ((unsigned long) (field[0])) | + (((unsigned long) (field[1])) << 8) | + (((unsigned long) (field[2])) << 16); + + case 4: + return ((unsigned long) (field[0])) | + (((unsigned long) (field[1])) << 8) | + (((unsigned long) (field[2])) << 16) | + (((unsigned long) (field[3])) << 24); + + case 5: + if (sizeof(u64) >= 8) { + return ((u64) (field[0])) | + (((u64) (field[1])) << 8) | + (((u64) (field[2])) << 16) | + (((u64) (field[3])) << 24) | + (((u64) (field[4])) << 32); + } + __fallthrough; + + case 6: + if (sizeof(u64) >= 8) { + return ((u64) (field[0])) | + (((u64) (field[1])) << 8) | + (((u64) (field[2])) << 16) | + (((u64) (field[3])) << 24) | + (((u64) (field[4])) << 32) | + (((u64) (field[5])) << 40); + } + __fallthrough; + + case 7: + if (sizeof(u64) >= 8) { + return ((u64) (field[0])) | + (((u64) (field[1])) << 8) | + (((u64) (field[2])) << 16) | + (((u64) (field[3])) << 24) | + (((u64) (field[4])) << 32) | + (((u64) (field[5])) << 40) | + (((u64) (field[6])) << 48); + } + __fallthrough; + + case 8: + if (sizeof(u64) >= 8) { + return ((u64) (field[0])) | + (((u64) (field[1])) << 8) | + (((u64) (field[2])) << 16) | + (((u64) (field[3])) << 24) | + (((u64) (field[4])) << 32) | + (((u64) (field[5])) << 40) | + (((u64) (field[6])) << 48) | + (((u64) (field[7])) << 56); + } + __fallthrough; + + default: + WARN("%s: Unhandled data length: %d\n", __func__, size); + } + return 0; +} + +/* + * Big endian helper. Adapted from binutils. + */ +u64 get_value_be(unsigned char *field, unsigned int size) +{ + switch (size) { + case 1: + return *field; + + case 2: + return ((unsigned int) (field[1])) | + (((int) (field[0])) << 8); + + case 3: + return ((unsigned long) (field[2])) | + (((unsigned long) (field[1])) << 8) | + (((unsigned long) (field[0])) << 16); + + case 4: + return ((unsigned long) (field[3])) | + (((unsigned long) (field[2])) << 8) | + (((unsigned long) (field[1])) << 16) | + (((unsigned long) (field[0])) << 24); + + case 5: + if (sizeof(u64) >= 8) { + return ((u64) (field[4])) | + (((u64) (field[3])) << 8) | + (((u64) (field[2])) << 16) | + (((u64) (field[1])) << 24) | + (((u64) (field[0])) << 32); + } + __fallthrough; + + case 6: + if (sizeof(u64) >= 8) { + return ((u64) (field[5])) | + (((u64) (field[4])) << 8) | + (((u64) (field[3])) << 16) | + (((u64) (field[2])) << 24) | + (((u64) (field[1])) << 32) | + (((u64) (field[0])) << 40); + } + __fallthrough; + + case 7: + if (sizeof(u64) >= 8) { + return ((u64) (field[6])) | + (((u64) (field[5])) << 8) | + (((u64) (field[4])) << 16) | + (((u64) (field[3])) << 24) | + (((u64) (field[2])) << 32) | + (((u64) (field[1])) << 40) | + (((u64) (field[0])) << 48); + } + __fallthrough; + + case 8: + if (sizeof(u64) >= 8) { + return ((u64) (field[7])) | + (((u64) (field[6])) << 8) | + (((u64) (field[5])) << 16) | + (((u64) (field[4])) << 24) | + (((u64) (field[3])) << 32) | + (((u64) (field[2])) << 40) | + (((u64) (field[1])) << 48) | + (((u64) (field[0])) << 56); + } + __fallthrough; + + default: + WARN("%s: Unhandled data length: %d\n", __func__, size); + } + return 0; +} + +/* + * LEB 128 read functions adapted from LLVM code. + */ +u64 read_uleb_128(unsigned char *start, unsigned char *end, + unsigned int *num_read, bool *fail) +{ + unsigned char *cur = start, byte; + unsigned int shift = 0; + u64 value = 0; + u64 slice; + + do { + if (cur == end) { + WARN("%s: op=%d end of data", __func__, op); + *num_read = (unsigned int) (cur - start); + *fail = true; + return 0; + } + + byte = *cur++; + slice = byte & 0x7f; + + if ((shift >= 64 && slice != 0) || + (slice << shift >> shift) != slice) { + WARN("%s: op=%d value too large", __func__, op); + *num_read = (unsigned int) (cur - start); + *fail = true; + return 0; + } + + value += slice << shift; + shift += 7; + } while (byte >= 128); + + *num_read = (unsigned int) (cur - start); + + return value; +} + +s64 read_sleb_128(unsigned char *start, unsigned char *end, + unsigned int *num_read, bool *fail) +{ + unsigned char *cur = start, byte; + unsigned int shift = 0; + s64 value = 0; + u64 slice; + + do { + if (cur == end) { + WARN("%s: op=%d end of data", __func__, op); + *num_read = (unsigned int) (cur - start); + *fail = true; + return 0; + } + + byte = *cur++; + slice = byte & 0x7f; + + if ((shift >= 64 && slice != (value < 0 ? 0x7f : 0x00)) || + (shift == 63 && slice != 0 && slice != 0x7f)) { + WARN("%s: op=%d value too large", __func__, op); + *num_read = (unsigned int) (cur - start); + *fail = true; + return 0; + } + + value |= slice << shift; + shift += 7; + } while (byte >= 128); + + if (shift < 64 && (byte & 0x40)) { + /* Sign extend negative numbers if needed. */ + value |= (-1ULL) << shift; + } + + *num_read = (unsigned int) (cur - start); + + return value; +} + +void dwarf_alloc_init(void) +{ + /* + * Use the size of the .debug_frame section as an estimate of the + * memory we need. + */ + free_size = debug_frame->data->d_size * 4; + free_space = malloc(free_size); + if (!free_space) { + WARN("%s: Could not optimize allocations", __func__); + free_size = 0; + } +} + +void *dwarf_alloc(size_t size) +{ + void *buf; + + /* Round to 8 bytes. */ + size = (size + 7) & ~7UL; + + if (free_size >= size) { + buf = free_space; + free_space += size; + free_size -= size; + return buf; + } + return malloc(size); +} diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 4b384c907027..85606a19f633 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -108,7 +108,7 @@ static struct section *find_section_by_index(struct elf *elf, return NULL; } -static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) +struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) { struct symbol *sym; diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h index 15ac0b7d3d6a..02b18149cdd7 100644 --- a/tools/objtool/include/objtool/builtin.h +++ b/tools/objtool/include/objtool/builtin.h @@ -15,5 +15,6 @@ extern int cmd_parse_options(int argc, const char **argv, const char * const usa extern int cmd_check(int argc, const char **argv); extern int cmd_orc(int argc, const char **argv); +extern int cmd_dwarf(int argc, const char **argv); #endif /* _BUILTIN_H */ diff --git a/tools/objtool/include/objtool/dwarf_def.h b/tools/objtool/include/objtool/dwarf_def.h new file mode 100644 index 000000000000..7a0a18480d2b --- /dev/null +++ b/tools/objtool/include/objtool/dwarf_def.h @@ -0,0 +1,438 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * dwarf_def.h - DWARF definitions for parsing DWARF information. + * + * Author: Madhavan T. Venkataraman (madvenka@xxxxxxxxxxxxxxxxxxx) + * + * Copyright (C) 2022 Microsoft Corporation + */ + +#ifndef _OBJTOOL_DWARF_DEF_H +#define _OBJTOOL_DWARF_DEF_H + +/* + * The DWARF Call Frame Information (CFI) is encoded in a self-contained + * section called .debug_frame. + * + * DWARF CFI defines the Canonical Frame Address (CFA) as the value of the + * stack pointer (SP) when a call instruction is executed. For the called + * function, other register values are expressed relative to the CFA. For + * a given code location within the function, one can compute things like: + * + * - what is the offset that must be added to the current stack pointer + * to get the CFA. + * + * - what offset must be subtracted from the CFA to obtain the current + * frame pointer (FP). + * + * - what offset must be subtracted from the CFA to obtain the location + * on the stack where a register value is saved. E.g., the return + * address (RA). + * + * - what register is saved in what register. + * + * - etc. + * + * This allows the unwinding of the stack. The unwinder starts at the top most + * frame and gets the value of the SP, FP and RA from the current register + * state. Using the DWARF CFI at the RA, the unwinder computes the values of + * the SP, FP and RA in the previous frame. This process continues until the + * SP hits the bottom of the stack and the unwinding terminates. + * + * In this work, the DWARF CFI is not used to build an unwinder. The existing + * frame pointer based unwinder is retained. But the CFI is used to compute + * an FP at every frame to validate the actual FP. If the computed and actual + * FPs match, then the stack frame is considered reliable. Otherwise, it is + * considered unreliable. If all of the frames in a stack trace are reliable, + * then the stack trace is reliable. + * + * Entries in a .debug_frame section are aligned on a multiple of the address + * size relative to the start of the section and come in two forms: + * + * - a Common Information Entry (CIE) and + * + * - a Frame Description Entry (FDE). + * + * A Common Information Entry holds information that is shared among many + * Frame Description Entries. So, it is like a header. There is at least one + * CIE in every non-empty .debug_frame section. + * + * The CIE contains information such as the size of an address in the + * architecture, the number of the return address register, etc. It also + * contains DWARF instructions to initialize unwind state at the start of + * an FDE. + * + * The FDE contains a code range to which it applies. It also contains DWARF + * instructions. These instructions are used to obtain the register rules + * at each code location. Using these rules, the SP, FP and RA are computed + * as mentioned above. + */ + +/* + * DWARF CFI defines the following rules to obtain the value of a register + * in the previous frame, given a current frame: + * + * 1. Same_Value: + * + * The current and previous values of the register are the same. + * + * 2. Val_Offset(N): + * + * The previous value is (CFA + N) where N is a signed offset. + * + * 3. Offset(N): + * + * The previous value is saved at (CFA + N). + * + * 4. register(R): + * + * The previous value is saved in register R. + * + * 5. Val_Expression(E): + * + * The previous value is the value produced by evaluating a given + * DWARF expression. DWARF expressions are evaluated on a stack. That + * is, operands are pushed and popped on a stack, operators are + * applied on them and the result is obtained. + * + * 6. Expression(E): + * + * The previous value is stored at the address computed from a DWARF + * expression. + * + * 7. Architectural: + * + * The previous value is obtained in an architecture-specific way via + * an architecture-specific "augmentor". The augmentors are vendor + * specific and are not part of the DWARF standard. + * + * Now, all of this is quite complicated. In this work, only (1), (2) and (3) + * will be supported. At the time of this writing, these are found to be + * sufficient for ARM64 and RISCV. Other architectures have not been checked. + * + * The code locations at which unsupported rules exist will be treated as + * unreliable from an unwinder perspective. In other words, if the RA of a + * stack frame is such a code location, then that frame is unreliable. + */ + +/* + * The following structure is used to encode the Same_Value, Offset(N) and + * the Val_Offset(N) rules. + * + * offset = 0, saved = true Never happens + * offset = 0, saved = false Same_Value + * offset = N, saved = true Offset(N) + * offset = N, saved = false Val_Offset(N) + */ +struct rule { + long offset; + bool saved; +}; + +/* + * Common Information Entry (CIE): + * + * next + * Next CIE in list. + * + * offset + * Section offset at which this CIE is found. + * + * length + * A constant that gives the number of bytes of the CIE structure, not + * including the length field itself. The size of the length field plus + * the value of length must be an integral multiple of the address size. + * + * id + * A constant that is used to distinguish CIEs from FDEs. + * + * version + * A version number. This number is specific to the call frame information + * and is independent of the DWARF version number. Versions 4 and above + * are not supported. + * + * address_size + * The size of a target address in this CIE and any FDEs that use it, + * in bytes. + * + * segment_size + * The size of a segment selector in this CIE and any FDEs that use it, + * in bytes. + * + * augmentation + * A null-terminated UTF-8 string that identifies the augmentation to + * this CIE or to the FDEs that use it. An augmentation is specified by + * an architecture to compute values in a way that is specific to that + * architecture. No augmentation is supported. + * + * code_factor + * A constant that is factored out of all advance location instructions. + * + * data_factor + * A constant that is factored out of certain offset instructions. + * + * return_address_reg + * The number of the return address register in the architecture. + * + * instructions + * DWARF instructions to initialize the unwind state at the start of + * an FDE. + * + * instructions_size + * Number of bytes of instructions. + * + * sp_rule + * Initial rule to compute the CFA derived from the above instructions. + * + * fp_rule + * Initial rule to compute the frame pointer derived from the above + * instructions. + * + * ra_rule + * Initial rule to compute the return address derived from the above + * instructions. + * + * saved_sp_rule, saved_fp_rule, saved_ra_rule + * Temporary storage to store and restore the CFA and frame pointer rules + * offsets while running instructions. + * + * cfa_reg, cfa_offset + * Temporary storage to remember the default CFA register and offset + * while running instructions. + * + * unusable + * Some error happened while processing CIE instructions. + */ +struct cie { + struct cie *next; + unsigned long offset; + unsigned long length; + unsigned long id; + unsigned char version; + unsigned char address_size; + unsigned char segment_size; + char *augmentation; + unsigned int code_factor; + int data_factor; + unsigned int return_address_reg; + unsigned char *instructions; + size_t instructions_size; + struct rule sp_rule; + struct rule fp_rule; + struct rule ra_rule; + struct rule saved_sp_rule; + struct rule saved_fp_rule; + struct rule saved_ra_rule; + unsigned int cfa_reg; + long cfa_offset; + bool unusable; +}; + +/* + * Frame Description Entry (FDE): + * + * next + * Next FDE in list. + * + * length + * A constant that gives the number of bytes of the header and instruction + * stream for this function, not including the length field itself. The + * size of the length field plus the value of length must be an integral + * multiple of the address size. + * + * cie_offset + * A constant offset into the .debug_frame section that denotes the CIE + * that is associated with this FDE. + * + * cie + * CIE for this FDE. + * + * segment_selector + * Segment selectors are not supported. + * + * start_pc, end_pc + * Range of code to which this FDE applies. + * + * instructions + * DWARF instructions to compute the register rules. + * + * instructions_size + * Number of bytes of instructions. + * + * index + * Index of the FDE record in the .debug_frame section. Used to obtain + * relocation information for the FDE. + * + * symbol + * Symbol information for the function for the code range. + * + * section + * Section information for the function. + * + * offset + * Offset within the section for the function. + * + * sp_offset + * Needed for clang hack. + */ +struct fde { + struct fde *next; + unsigned long length; + unsigned long cie_offset; + struct cie *cie; + unsigned long segment_selector; + unsigned long start_pc; + unsigned long end_pc; + unsigned char *instructions; + size_t instructions_size; + unsigned long index; + struct symbol *symbol; + struct section *section; + unsigned long offset; + unsigned long sp_offset; +}; + +/* + * These are identifiers for 32-bit and 64-bit CIE entries respectively. + * These identifiers distinguish a CIE from an FDE in .debug_frame. + */ +#define CIE_ID_32 0xFFFFFFFF +#define CIE_ID_64 0xFFFFFFFFFFFFFFFFUL + +/* + * DWARF instruction op codes. + */ + +/* Primary op codes in the high 2 bits */ + +#define DW_CFA_extended_op 0x00 +#define DW_CFA_advance_loc 0x40 +#define DW_CFA_offset 0x80 +#define DW_CFA_restore 0xc0 + +/* Extended op codes in the low 6 bits */ + +#define DW_CFA_nop 0x00 +#define DW_CFA_set_loc 0x01 +#define DW_CFA_advance_loc1 0x02 +#define DW_CFA_advance_loc2 0x03 +#define DW_CFA_advance_loc4 0x04 +#define DW_CFA_offset_extended 0x05 +#define DW_CFA_restore_extended 0x06 +#define DW_CFA_undefined 0x07 +#define DW_CFA_same_value 0x08 +#define DW_CFA_register 0x09 +#define DW_CFA_remember_state 0x0a +#define DW_CFA_restore_state 0x0b +#define DW_CFA_def_cfa 0x0c +#define DW_CFA_def_cfa_register 0x0d +#define DW_CFA_def_cfa_offset 0x0e +/* DWARF 3. */ +#define DW_CFA_def_cfa_expression 0x0f +#define DW_CFA_expression 0x10 +#define DW_CFA_offset_extended_sf 0x11 +#define DW_CFA_def_cfa_sf 0x12 +#define DW_CFA_def_cfa_offset_sf 0x13 +#define DW_CFA_val_offset 0x14 +#define DW_CFA_val_offset_sf 0x15 +#define DW_CFA_val_expression 0x16 +#define DW_CFA_lo_user 0x1c +#define DW_CFA_hi_user 0x3f + +/* + * Extract a value directly from the DWARF instruction stream. Must take into + * account endianness. + */ +#define GET_VALUE(value, start, end, count) \ + do { \ + size_t _size = (count); \ + size_t _avail = (end) - (start); \ + \ + if (sizeof(value) < _size) \ + _size = sizeof(value); \ + if ((start) > (end)) \ + _avail = 0; \ + if (_size > _avail) \ + _size = _avail; \ + if (_size == 0) \ + (value) = 0; \ + else \ + (value) = get_value((start), _size); \ + (start) += _size; \ + } while (0) + +/* + * Extract an unsigned integer expressed in LEB 128 format from the DWARF + * instruction stream. + */ +#define READ_ULEB_128(value, start, end, fail) \ + do { \ + u64 _val; \ + unsigned int _len; \ + bool _fail = false; \ + \ + _val = read_uleb_128(start, end, &_len, &_fail); \ + \ + start += _len; \ + (value) = _val; \ + if ((value) != _val) { \ + WARN("READ_ULEB_128: op=%d value mismatch", op);\ + _fail = true; \ + } \ + if (_fail) \ + (fail) = true; \ + } while (0) + +/* + * Extract a signed integer expressed in LEB 128 format from the DWARF + * instruction stream. + */ +#define READ_SLEB_128(value, start, end, fail) \ + do { \ + s64 _val; \ + unsigned int _len; \ + bool _fail = false; \ + \ + _val = read_sleb_128(start, end, &_len, &_fail); \ + \ + start += _len; \ + (value) = _val; \ + if ((value) != _val) { \ + WARN("READ_SLEB_128: op=%d value mismatch", op);\ + _fail = true; \ + } \ + if (_fail) \ + (fail) = true; \ + } while (0) + +extern struct objtool_file *dwarf_file; +extern struct section *debug_frame; +extern struct cie *cies, *cur_cie; +extern struct fde *fdes, *cur_fde; +extern unsigned char op, operand; +extern void *free_space; +extern size_t free_size; +extern u64 (*get_value)(unsigned char *field, unsigned int size); + +void dwarf_rule_start(struct fde *fde); +int dwarf_rule_add(struct fde *fde, unsigned long addr, + struct rule *sp_rule, struct rule *fp_rule); +void dwarf_rule_next(struct fde *fde, unsigned long addr); +void dwarf_rule_reset(struct fde *fde); +int arch_dwarf_fde_reloc(struct fde *fde); +void arch_dwarf_clang_hack(struct fde *fde, unsigned long pc, + struct rule *sp_rule, struct rule *fp_rule); +int arch_dwarf_check_rules(struct fde *fde, unsigned long pc, + struct rule *sp_rule, struct rule *fp_rule, + struct rule *ra_rule); +u64 get_value_le(unsigned char *field, unsigned int size); +u64 get_value_be(unsigned char *field, unsigned int size); +u64 read_uleb_128(unsigned char *start, unsigned char *end, + unsigned int *num_read, bool *fail); +s64 read_sleb_128(unsigned char *start, unsigned char *end, + unsigned int *num_read, bool *fail); +void dwarf_parse_instructions(void); +void dwarf_alloc_init(void); +void *dwarf_alloc(size_t size); + +#endif /* _OBJTOOL_DWARF_DEF_H */ diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index cdc739fa9a6f..c133ece2cdcf 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -151,6 +151,7 @@ struct section *find_section_by_name(const struct elf *elf, const char *name); struct symbol *find_func_by_offset(struct section *sec, unsigned long offset); struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset); struct symbol *find_symbol_by_name(const struct elf *elf, const char *name); +struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx); struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset); struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset); struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec, diff --git a/tools/objtool/include/objtool/objtool.h b/tools/objtool/include/objtool/objtool.h index f99fbc6078d5..0344e89a10e8 100644 --- a/tools/objtool/include/objtool/objtool.h +++ b/tools/objtool/include/objtool/objtool.h @@ -41,5 +41,6 @@ void objtool_pv_add(struct objtool_file *file, int idx, struct symbol *func); int check(struct objtool_file *file); int orc_dump(const char *objname); int orc_create(struct objtool_file *file); +int dwarf_parse(struct objtool_file *file); #endif /* _OBJTOOL_H */ diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c index bdf699f6552b..bfb9c5607cfc 100644 --- a/tools/objtool/objtool.c +++ b/tools/objtool/objtool.c @@ -38,6 +38,7 @@ static const char objtool_usage_string[] = static struct cmd_struct objtool_cmds[] = { {"check", cmd_check, "Perform stack metadata validation on an object file" }, {"orc", cmd_orc, "Generate in-place ORC unwind tables for an object file" }, + {"dwarf", cmd_dwarf, "Generate DWARF rules for object file"}, }; bool help; diff --git a/tools/objtool/weak.c b/tools/objtool/weak.c index 8314e824db4a..67b5016a8327 100644 --- a/tools/objtool/weak.c +++ b/tools/objtool/weak.c @@ -8,6 +8,7 @@ #include <stdbool.h> #include <errno.h> #include <objtool/objtool.h> +#include <objtool/dwarf_def.h> #define UNSUPPORTED(name) \ ({ \ @@ -29,3 +30,29 @@ int __weak orc_create(struct objtool_file *file) { UNSUPPORTED("orc"); } + +int __weak dwarf_parse(struct objtool_file *file) + +{ + fprintf(stderr, "error: objtool: %s not implemented\n", __func__); + return -EOPNOTSUPP; +} + +int __weak arch_dwarf_fde_reloc(struct fde *fde) +{ + fprintf(stderr, "error: objtool: %s not implemented\n", __func__); + return -EOPNOTSUPP; +} + +void __weak arch_dwarf_clang_hack(struct fde *fde, unsigned long pc, + struct rule *sp_rule, struct rule *fp_rule) +{ +} + +int __weak arch_dwarf_check_rules(struct fde *fde, unsigned long pc, + struct rule *sp_rule, struct rule *fp_rule, + struct rule *ra_rule) +{ + fprintf(stderr, "error: objtool: %s not implemented\n", __func__); + return -EOPNOTSUPP; +} -- 2.25.1
