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Message-ID: <20251018142124.783206-4-dongml2@chinatelecom.cn>
Date: Sat, 18 Oct 2025 22:21:22 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org,
jolsa@...nel.org
Cc: daniel@...earbox.net,
john.fastabend@...il.com,
andrii@...nel.org,
martin.lau@...ux.dev,
eddyz87@...il.com,
song@...nel.org,
yonghong.song@...ux.dev,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
mattbobrowski@...gle.com,
rostedt@...dmis.org,
mhiramat@...nel.org,
mathieu.desnoyers@...icios.com,
leon.hwang@...ux.dev,
bpf@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Subject: [PATCH RFC bpf-next 3/5] bpf,x86: add tracing session supporting for x86_64
Add BPF_TRACE_SESSION supporting to x86_64. invoke_bpf_session_entry and
invoke_bpf_session_exit is introduced for this purpose.
In invoke_bpf_session_entry(), we will check if the return value of the
fentry is 0, and clear the corresponding flag if not. And in
invoke_bpf_session_exit(), we will check if the corresponding flag is
set. If not set, the fexit will be skipped.
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
Co-developed-by: Leon Hwang <leon.hwang@...ux.dev>
Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
---
arch/x86/net/bpf_jit_comp.c | 115 +++++++++++++++++++++++++++++++++++-
1 file changed, 114 insertions(+), 1 deletion(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index d4c93d9e73e4..0586b96ed529 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -3108,6 +3108,97 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
return 0;
}
+static int invoke_bpf_session_entry(const struct btf_func_model *m, u8 **pprog,
+ struct bpf_tramp_links *tl, int stack_size,
+ int run_ctx_off, int session_off,
+ void *image, void *rw_image)
+{
+ u64 session_flags;
+ u8 *prog = *pprog;
+ u8 *jmp_insn;
+ int i;
+
+ /* clear the session flags:
+ *
+ * xor rax, rax
+ * mov QWORD PTR [rbp - session_off], rax
+ */
+ EMIT3(0x48, 0x31, 0xC0);
+ emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_0, -session_off);
+
+ for (i = 0; i < tl->nr_links; i++) {
+ if (invoke_bpf_prog(m, &prog, tl->links[i], stack_size, run_ctx_off, true,
+ image, rw_image))
+ return -EINVAL;
+
+ /* fentry prog stored return value into [rbp - 8]. Emit:
+ * if (*(u64 *)(rbp - 8) != 0)
+ * *(u64 *)(rbp - session_off) |= (1 << (i + 1));
+ */
+ /* cmp QWORD PTR [rbp - 0x8], 0x0 */
+ EMIT4(0x48, 0x83, 0x7d, 0xf8); EMIT1(0x00);
+ /* emit 2 nops that will be replaced with JE insn */
+ jmp_insn = prog;
+ emit_nops(&prog, 2);
+
+ session_flags = (1ULL << (i + 1));
+ /* mov rax, $session_flags */
+ emit_mov_imm64(&prog, BPF_REG_0, session_flags >> 32, (u32) session_flags);
+ /* or QWORD PTR [rbp - session_off], rax */
+ EMIT2(0x48, 0x09);
+ emit_insn_suffix(&prog, BPF_REG_FP, BPF_REG_0, -session_off);
+
+ jmp_insn[0] = X86_JE;
+ jmp_insn[1] = prog - jmp_insn - 2;
+ }
+
+ *pprog = prog;
+ return 0;
+}
+
+static int invoke_bpf_session_exit(const struct btf_func_model *m, u8 **pprog,
+ struct bpf_tramp_links *tl, int stack_size,
+ int run_ctx_off, int session_off,
+ void *image, void *rw_image)
+{
+ u64 session_flags;
+ u8 *prog = *pprog;
+ u8 *jmp_insn;
+ int i;
+
+ /* set the bpf_trace_is_exit flag to the session flags */
+ /* mov rax, 1 */
+ emit_mov_imm32(&prog, false, BPF_REG_0, 1);
+ /* or QWORD PTR [rbp - session_off], rax */
+ EMIT2(0x48, 0x09);
+ emit_insn_suffix(&prog, BPF_REG_FP, BPF_REG_0, -session_off);
+
+ for (i = 0; i < tl->nr_links; i++) {
+ /* check if (1 << (i+1)) is set in the session flags, and
+ * skip the execution of the fexit program if it is.
+ */
+ session_flags = 1ULL << (i + 1);
+ /* mov rax, $session_flags */
+ emit_mov_imm64(&prog, BPF_REG_1, session_flags >> 32, (u32) session_flags);
+ /* test QWORD PTR [rbp - session_off], rax */
+ EMIT2(0x48, 0x85);
+ emit_insn_suffix(&prog, BPF_REG_FP, BPF_REG_1, -session_off);
+ /* emit 2 nops that will be replaced with JE insn */
+ jmp_insn = prog;
+ emit_nops(&prog, 2);
+
+ if (invoke_bpf_prog(m, &prog, tl->links[i], stack_size, run_ctx_off, false,
+ image, rw_image))
+ return -EINVAL;
+
+ jmp_insn[0] = X86_JNE;
+ jmp_insn[1] = prog - jmp_insn - 2;
+ }
+
+ *pprog = prog;
+ return 0;
+}
+
/* 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;
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
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