On Sat, Oct 18, 2025 at 10:21:22PM +0800, Menglong Dong wrote:
SNIP
> /* mov rax, qword ptr [rbp - rounded_stack_depth - 8] */
> #define LOAD_TRAMP_TAIL_CALL_CNT_PTR(stack) \
> __LOAD_TCC_PTR(-round_up(stack, 8) - 8)
> @@ -3179,8 +3270,10 @@ static int __arch_prepare_bpf_trampoline(struct
> bpf_tramp_image *im, void *rw_im
> void *func_addr)
> {
> int i, ret, nr_regs = m->nr_args, stack_size = 0;
> - int regs_off, nregs_off, ip_off, run_ctx_off, arg_stack_off, rbx_off;
> + int regs_off, nregs_off, session_off, ip_off, run_ctx_off,
> + arg_stack_off, rbx_off;
> struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
> + struct bpf_tramp_links *session = &tlinks[BPF_TRAMP_SESSION];
> 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;
> @@ -3222,6 +3315,8 @@ static int __arch_prepare_bpf_trampoline(struct
> bpf_tramp_image *im, void *rw_im
> *
> * RBP - nregs_off [ regs count ] always
> *
> + * RBP - session_off [ session flags ] tracing session
> + *
> * RBP - ip_off [ traced function ] BPF_TRAMP_F_IP_ARG flag
> *
> * RBP - rbx_off [ rbx value ] always
> @@ -3246,6 +3341,8 @@ static int __arch_prepare_bpf_trampoline(struct
> bpf_tramp_image *im, void *rw_im
> /* regs count */
> stack_size += 8;
> nregs_off = stack_size;
> + stack_size += 8;
> + session_off = stack_size;
should this depend on session->nr_links ?
jirka
>
> if (flags & BPF_TRAMP_F_IP_ARG)
> stack_size += 8; /* room for IP address argument */
> @@ -3345,6 +3442,13 @@ static int __arch_prepare_bpf_trampoline(struct
> bpf_tramp_image *im, void *rw_im
> return -EINVAL;
> }
>
> + if (session->nr_links) {
> + if (invoke_bpf_session_entry(m, &prog, session, regs_off,
> + run_ctx_off, session_off,
> + image, rw_image))
> + return -EINVAL;
> + }
> +
> if (fmod_ret->nr_links) {
> branches = kcalloc(fmod_ret->nr_links, sizeof(u8 *),
> GFP_KERNEL);
> @@ -3409,6 +3513,15 @@ static int __arch_prepare_bpf_trampoline(struct
> bpf_tramp_image *im, void *rw_im
> }
> }
>
> + if (session->nr_links) {
> + if (invoke_bpf_session_exit(m, &prog, session, regs_off,
> + run_ctx_off, session_off,
> + image, rw_image)) {
> + ret = -EINVAL;
> + goto cleanup;
> + }
> + }
> +
> if (flags & BPF_TRAMP_F_RESTORE_REGS)
> restore_regs(m, &prog, regs_off);
>
> --
> 2.51.0
>
