In C, struct value can be passed as a function argument. For small structs, struct value may be passed in one or more registers. For trampoline based bpf programs, This would cause complication since one-to-one mapping between function argument and arch argument register is not valid any more. The latest llvm16 added bpf support to pass by values for struct up to 16 bytes ([1]). This is also true for x86_64 architecture where two registers will hold the struct value if the struct size is >8 and <= 16. This may not be true if one of struct member is 'double' type but in current linux source code we don't have such instance yet, so we assume all >8 && <= 16 struct holds two general purpose argument registers. Also change on-stack nr_args value to the number of registers holding the arguments. This will permit bpf_get_func_arg() helper to get all argument values. [1] https://reviews.llvm.org/D132144 Signed-off-by: Yonghong Song <yhs@xxxxxx> --- arch/x86/net/bpf_jit_comp.c | 68 +++++++++++++++++++++++++++---------- 1 file changed, 51 insertions(+), 17 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index c1f6c1c51d99..ae89f4143eb4 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1751,34 +1751,60 @@ st: if (is_imm8(insn->off)) static void save_regs(const struct btf_func_model *m, u8 **prog, int nr_args, int stack_size) { - int i; + int i, j, arg_size, nr_regs; /* Store function arguments to stack. * For a function that accepts two pointers the sequence will be: * mov QWORD PTR [rbp-0x10],rdi * mov QWORD PTR [rbp-0x8],rsi */ - for (i = 0; i < min(nr_args, 6); i++) - emit_stx(prog, bytes_to_bpf_size(m->arg_size[i]), - BPF_REG_FP, - i == 5 ? X86_REG_R9 : BPF_REG_1 + i, - -(stack_size - i * 8)); + for (i = 0, j = 0; i < min(nr_args, 6); i++) { + if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) { + nr_regs = (m->arg_size[i] + 7) / 8; + arg_size = 8; + } else { + nr_regs = 1; + arg_size = m->arg_size[i]; + } + + while (nr_regs) { + emit_stx(prog, bytes_to_bpf_size(arg_size), + BPF_REG_FP, + j == 5 ? X86_REG_R9 : BPF_REG_1 + j, + -(stack_size - j * 8)); + nr_regs--; + j++; + } + } } static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_args, int stack_size) { - int i; + int i, j, arg_size, nr_regs; /* Restore function arguments from stack. * For a function that accepts two pointers the sequence will be: * EMIT4(0x48, 0x8B, 0x7D, 0xF0); mov rdi,QWORD PTR [rbp-0x10] * EMIT4(0x48, 0x8B, 0x75, 0xF8); mov rsi,QWORD PTR [rbp-0x8] */ - for (i = 0; i < min(nr_args, 6); i++) - emit_ldx(prog, bytes_to_bpf_size(m->arg_size[i]), - i == 5 ? X86_REG_R9 : BPF_REG_1 + i, - BPF_REG_FP, - -(stack_size - i * 8)); + for (i = 0, j = 0; i < min(nr_args, 6); i++) { + if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) { + nr_regs = (m->arg_size[i] + 7) / 8; + arg_size = 8; + } else { + nr_regs = 1; + arg_size = m->arg_size[i]; + } + + while (nr_regs) { + emit_ldx(prog, bytes_to_bpf_size(arg_size), + j == 5 ? X86_REG_R9 : BPF_REG_1 + j, + BPF_REG_FP, + -(stack_size - j * 8)); + nr_regs--; + j++; + } + } } static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog, @@ -2015,7 +2041,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i struct bpf_tramp_links *tlinks, void *orig_call) { - int ret, i, nr_args = m->nr_args; + int ret, i, nr_args = m->nr_args, extra_nregs = 0; int regs_off, ip_off, args_off, stack_size = nr_args * 8, run_ctx_off; struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY]; struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT]; @@ -2028,6 +2054,14 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i if (nr_args > 6) return -ENOTSUPP; + for (i = 0; i < MAX_BPF_FUNC_ARGS; i++) { + if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) + extra_nregs += (m->arg_size[i] + 7) / 8 - 1; + } + if (nr_args + extra_nregs > 6) + return -ENOTSUPP; + stack_size += extra_nregs * 8; + /* Generated trampoline stack layout: * * RBP + 8 [ return address ] @@ -2040,7 +2074,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i * [ ... ] * RBP - regs_off [ reg_arg1 ] program's ctx pointer * - * RBP - args_off [ args count ] always + * RBP - args_off [ arg regs count ] always * * RBP - ip_off [ traced function ] BPF_TRAMP_F_IP_ARG flag * @@ -2083,11 +2117,11 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i EMIT4(0x48, 0x83, 0xEC, stack_size); /* sub rsp, stack_size */ EMIT1(0x53); /* push rbx */ - /* Store number of arguments of the traced function: - * mov rax, nr_args + /* Store number of argument registers of the traced function: + * mov rax, nr_args + extra_nregs * mov QWORD PTR [rbp - args_off], rax */ - emit_mov_imm64(&prog, BPF_REG_0, 0, (u32) nr_args); + emit_mov_imm64(&prog, BPF_REG_0, 0, (u32) nr_args + extra_nregs); emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -args_off); if (flags & BPF_TRAMP_F_IP_ARG) { -- 2.30.2
