2024-10-31 13:36 UTC+0800 ~ Leon Hwang <hffilwlqm@xxxxxxxxx> > > > On 2024/10/31 13:27, Leon Hwang wrote: >> >> >> On 2024/10/31 08:27, Quentin Monnet wrote: >>> 2024-10-30 17:47 UTC+0800 ~ Leon Hwang <hffilwlqm@xxxxxxxxx> >>>> From: Leon Hwang <leon.hwang@xxxxxxxxx> >>>> >>>> This patch addresses the bpftool issue "Wrong callq address displayed"[0]. >>>> >>>> The issue stemmed from an incorrect program counter (PC) value used during >>>> disassembly with LLVM or libbfd. To calculate the correct address for >>>> relative calls, the PC argument must reflect the actual address in the >>>> kernel. >>>> >>>> [0] https://github.com/libbpf/bpftool/issues/109 >>>> >>>> Fixes: e1947c750ffe ("bpftool: Refactor disassembler for JIT-ed programs") >>>> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx> >>>> --- >>>> tools/bpf/bpftool/jit_disasm.c | 6 +++--- >>>> 1 file changed, 3 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c >>>> index 7b8d9ec89ebd3..fe8fabba4b05f 100644 >>>> --- a/tools/bpf/bpftool/jit_disasm.c >>>> +++ b/tools/bpf/bpftool/jit_disasm.c >>>> @@ -114,8 +114,7 @@ disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc) >>>> char buf[256]; >>>> int count; >>>> >>>> - count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, pc, >>>> - buf, sizeof(buf)); >>>> + count = LLVMDisasmInstruction(*ctx, image, len, pc, buf, sizeof(buf)); >>>> if (json_output) >>>> printf_json(buf); >>>> else >>>> @@ -360,7 +359,8 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, >>>> printf("%4x:" DISASM_SPACER, pc); >>>> } >>>> >>>> - count = disassemble_insn(&ctx, image, len, pc); >>>> + count = disassemble_insn(&ctx, image + pc, len - pc, >>>> + func_ksym + pc); >>> >>> Thanks a lot for looking into this! Your patch does solve the issue for >>> the LLVM disassembler (nice!), but it breaks the libbfd one: >>> >>> >>> $ ./bpftool version | grep features >>> features: libbfd >>> # ./bpftool prog dump j id 111 op >>> int xdp_redirect_map_0(struct xdp_md * xdp): >>> bpf_prog_a8f6f9c4be77b94c_xdp_redirect_map_0: >>> ; return bpf_redirect_map(&tx_port, 0, 0); >>> 0: Address 0xffffffffc01ae950 is out of bounds. >>> >>> I don't think we can change the PC in the case of libbfd, as far as I >>> can tell it needs to point to the first instruction to disassemble. Two >>> of the arguments we pass to disassemble_insn(), image and len, are >>> ignored by the libbfd disassembler; so it leaves only the ctx argument >>> that we can maybe update to pass the func_ksym, but I haven't found how >>> to do that yet (if possible at all). >>> >>> Thanks, >>> Quentin >>> >> >> Hi Quentin, >> >> After diving into the details of libbfd, I’ve found a way to correct the >> callq address. By adjusting the relative addresses using func_ksym >> within a custom info->print_addr_func, we can achieve accurate results. >> >> Here’s the updated patch: >> >> From 687f165fe79b67ba457672bb682bde3d916ce0cd Mon Sep 17 00:00:00 2001 >> From: Leon Hwang <leon.hwang@xxxxxxxxx> >> Date: Thu, 31 Oct 2024 13:00:05 +0800 >> Subject: [PATCH bpf v2] bpf, bpftool: Fix incorrect disasm pc >> >> This patch addresses the bpftool issue "Wrong callq address displayed"[0]. >> >> The issue stemmed from an incorrect program counter (PC) value used during >> disassembly with LLVM or libbfd. >> >> For LLVM: The PC argument must represent the actual address in the kernel >> to compute the correct relative address. >> >> For libbfd: The relative address can be adjusted by adding func_ksym within >> the custom info->print_address_func to yield the correct address. >> >> [0] https://github.com/libbpf/bpftool/issues/109 >> >> Fixes: e1947c750ffe ("bpftool: Refactor disassembler for JIT-ed programs") >> Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx> >> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx> >> --- >> tools/bpf/bpftool/jit_disasm.c | 40 ++++++++++++++++++++++++---------- >> 1 file changed, 29 insertions(+), 11 deletions(-) >> >> diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c >> index 7b8d9ec89..f76d4bf0c 100644 >> --- a/tools/bpf/bpftool/jit_disasm.c >> +++ b/tools/bpf/bpftool/jit_disasm.c >> @@ -80,7 +80,8 @@ symbol_lookup_callback(__maybe_unused void *disasm_info, >> static int >> init_context(disasm_ctx_t *ctx, const char *arch, >> __maybe_unused const char *disassembler_options, >> - __maybe_unused unsigned char *image, __maybe_unused ssize_t len) >> + __maybe_unused unsigned char *image, __maybe_unused ssize_t len, >> + __maybe_unused __u64 func_ksym) >> { >> char *triple; >> >> @@ -109,12 +110,13 @@ static void destroy_context(disasm_ctx_t *ctx) >> } >> >> static int >> -disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, >> int pc) >> +disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, >> int pc, >> + __u64 func_ksym) >> { >> char buf[256]; >> int count; >> >> - count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, pc, >> + count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, func_ksym + pc, >> buf, sizeof(buf)); >> if (json_output) >> printf_json(buf); >> @@ -137,7 +139,20 @@ int disasm_init(void) >> #define DISASM_SPACER "\t" >> >> typedef struct { >> - struct disassemble_info *info; >> + struct disassemble_info info; >> + __u64 func_ksym; >> +} disasm_info; I don't think we need a typdef for this one? >> + >> +static void disasm_print_addr(bfd_vma addr, struct disassemble_info *info) >> +{ >> + disasm_info *dinfo = container_of(info, disasm_info, info); >> + >> + addr += dinfo->func_ksym; >> + generic_print_address(addr, info); >> +} >> + >> +typedef struct { >> + disasm_info *info; >> disassembler_ftype disassemble; >> bfd *bfdf; >> } disasm_ctx_t; >> @@ -215,7 +230,7 @@ static int fprintf_json_styled(void *out, >> >> static int init_context(disasm_ctx_t *ctx, const char *arch, >> const char *disassembler_options, >> - unsigned char *image, ssize_t len) >> + unsigned char *image, ssize_t len, __u64 func_ksym) >> { >> struct disassemble_info *info; >> char tpath[PATH_MAX]; >> @@ -238,12 +253,13 @@ static int init_context(disasm_ctx_t *ctx, const >> char *arch, >> } >> bfdf = ctx->bfdf; >> >> - ctx->info = malloc(sizeof(struct disassemble_info)); >> + ctx->info = malloc(sizeof(disasm_info)); >> if (!ctx->info) { >> p_err("mem alloc failed"); >> goto err_close; >> } >> - info = ctx->info; >> + ctx->info->func_ksym = func_ksym; >> + info = &ctx->info->info; >> >> if (json_output) >> init_disassemble_info_compat(info, stdout, >> @@ -272,6 +288,7 @@ static int init_context(disasm_ctx_t *ctx, const >> char *arch, >> info->disassembler_options = disassembler_options; >> info->buffer = image; >> info->buffer_length = len; >> + info->print_address_func = disasm_print_addr; >> >> disassemble_init_for_target(info); >> >> @@ -304,9 +321,10 @@ static void destroy_context(disasm_ctx_t *ctx) >> >> static int >> disassemble_insn(disasm_ctx_t *ctx, __maybe_unused unsigned char *image, >> - __maybe_unused ssize_t len, int pc) >> + __maybe_unused ssize_t len, __u64 pc, > > NIT: type of pc should keep int Yep. Can you please send a v3 with this fix? So that patchwork can pick it up properly. I tested your v2 and it works for both disassemblers, thanks a lot! Quentin
