On Fri, Sep 09, 2022 at 12:12:42PM +0200, Jiri Olsa wrote:
> Using function address given at the generation time as the trampoline
> ip argument. This way we get directly the function address that we
> need, so we don't need to:
> - read the ip from the stack
> - subtract X86_PATCH_SIZE
> - subtract ENDBR_INSN_SIZE if CONFIG_X86_KERNEL_IBT is enabled
> which is not even implemented yet ;-)
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index ae89f4143eb4..1047686cc545 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2039,13 +2039,14 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
> int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
> const struct btf_func_model *m, u32 flags,
> struct bpf_tramp_links *tlinks,
> - void *orig_call)
> + void *func_addr)
> {
> 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];
> struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
> + void *orig_call = func_addr;
> u8 **branches = NULL;
> u8 *prog;
> bool save_ret;
> @@ -2126,12 +2127,10 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
>
> if (flags & BPF_TRAMP_F_IP_ARG) {
> /* Store IP address of the traced function:
> - * mov rax, QWORD PTR [rbp + 8]
> - * sub rax, X86_PATCH_SIZE
> + * mov rax, func_addr
Shouldn't that be: movabs? Regular mov can't do 64bit immediates.
Also curse Intel syntax, this is bloody unreadable.
> * mov QWORD PTR [rbp - ip_off], rax
> */
> - emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, 8);
> - EMIT4(0x48, 0x83, 0xe8, X86_PATCH_SIZE);
> + emit_mov_imm64(&prog, BPF_REG_0, (long) func_addr >> 32, (u32) (long) func_addr);
> emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -ip_off);
> }
>
> --
> 2.37.3
>
