From: Menglong Dong <menglong8.dong@gmail.com>
To: ast@kernel.org, andrii@kernel.org
Cc: davem@davemloft.net, dsahern@kernel.org, daniel@iogearbox.net,
martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org,
yonghong.song@linux.dev, john.fastabend@gmail.com,
kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com,
jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
hpa@zytor.com, netdev@vger.kernel.org, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH bpf-next v4 2/9] bpf: use last 8-bits for the nr_args in trampoline
Date: Wed, 17 Dec 2025 17:54:38 +0800 [thread overview]
Message-ID: <20251217095445.218428-3-dongml2@chinatelecom.cn> (raw)
In-Reply-To: <20251217095445.218428-1-dongml2@chinatelecom.cn>
For now, ctx[-1] is used to store the nr_args in the trampoline. However,
1-byte is enough to store such information. Therefor, we use only the last
byts of ctx[-1] to store the nr_args, and reverve the rest for other
usages.
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
kernel/bpf/verifier.c | 35 +++++++++++++++++++----------------
kernel/trace/bpf_trace.c | 4 ++--
2 files changed, 21 insertions(+), 18 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d399bfd2413f..96753833c090 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23275,15 +23275,16 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
insn->imm == BPF_FUNC_get_func_arg) {
/* Load nr_args from ctx - 8 */
insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
- insn_buf[1] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6);
- insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3);
- insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
- insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0);
- insn_buf[5] = BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0);
- insn_buf[6] = BPF_MOV64_IMM(BPF_REG_0, 0);
- insn_buf[7] = BPF_JMP_A(1);
- insn_buf[8] = BPF_MOV64_IMM(BPF_REG_0, -EINVAL);
- cnt = 9;
+ insn_buf[1] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF);
+ insn_buf[2] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6);
+ insn_buf[3] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3);
+ insn_buf[4] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
+ insn_buf[5] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0);
+ insn_buf[6] = BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0);
+ insn_buf[7] = BPF_MOV64_IMM(BPF_REG_0, 0);
+ insn_buf[8] = BPF_JMP_A(1);
+ insn_buf[9] = BPF_MOV64_IMM(BPF_REG_0, -EINVAL);
+ cnt = 10;
new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
if (!new_prog)
@@ -23303,12 +23304,13 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
eatype == BPF_MODIFY_RETURN) {
/* Load nr_args from ctx - 8 */
insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
- insn_buf[1] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3);
- insn_buf[2] = BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1);
- insn_buf[3] = BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0);
- insn_buf[4] = BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0);
- insn_buf[5] = BPF_MOV64_IMM(BPF_REG_0, 0);
- cnt = 6;
+ insn_buf[1] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF);
+ insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_0, 3);
+ insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1);
+ insn_buf[4] = BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0);
+ insn_buf[5] = BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_3, 0);
+ insn_buf[6] = BPF_MOV64_IMM(BPF_REG_0, 0);
+ cnt = 7;
} else {
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, -EOPNOTSUPP);
cnt = 1;
@@ -23329,8 +23331,9 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
insn->imm == BPF_FUNC_get_func_arg_cnt) {
/* Load nr_args from ctx - 8 */
insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+ insn_buf[1] = BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 0xFF);
- new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);
+ new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 2);
if (!new_prog)
return -ENOMEM;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d57727abaade..10c9992d2745 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1194,7 +1194,7 @@ const struct bpf_func_proto bpf_get_branch_snapshot_proto = {
BPF_CALL_3(get_func_arg, void *, ctx, u32, n, u64 *, value)
{
/* This helper call is inlined by verifier. */
- u64 nr_args = ((u64 *)ctx)[-1];
+ u64 nr_args = ((u64 *)ctx)[-1] & 0xFF;
if ((u64) n >= nr_args)
return -EINVAL;
@@ -1214,7 +1214,7 @@ static const struct bpf_func_proto bpf_get_func_arg_proto = {
BPF_CALL_2(get_func_ret, void *, ctx, u64 *, value)
{
/* This helper call is inlined by verifier. */
- u64 nr_args = ((u64 *)ctx)[-1];
+ u64 nr_args = ((u64 *)ctx)[-1] & 0xFF;
*value = ((u64 *)ctx)[nr_args];
return 0;
--
2.52.0
next prev parent reply other threads:[~2025-12-17 9:55 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-17 9:54 [PATCH bpf-next v4 0/9] bpf: tracing session supporting Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 1/9] bpf: add tracing session support Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:24 ` Menglong Dong
2025-12-17 9:54 ` Menglong Dong [this message]
2025-12-17 9:54 ` [PATCH bpf-next v4 3/9] bpf: add the kfunc bpf_fsession_is_return Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 4/9] bpf: add the kfunc bpf_fsession_cookie Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:31 ` Menglong Dong
2025-12-19 12:01 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 5/9] bpf,x86: introduce emit_st_r0_imm64() for trampoline Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 6/9] bpf,x86: add tracing session supporting for x86_64 Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:41 ` Menglong Dong
2025-12-19 16:56 ` Andrii Nakryiko
2025-12-17 9:54 ` [PATCH bpf-next v4 7/9] libbpf: add support for tracing session Menglong Dong
2025-12-19 0:55 ` Andrii Nakryiko
2025-12-19 1:42 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 8/9] selftests/bpf: add testcases " Menglong Dong
2025-12-17 10:24 ` bot+bpf-ci
2025-12-17 11:42 ` Menglong Dong
2025-12-17 9:54 ` [PATCH bpf-next v4 9/9] selftests/bpf: test fsession mixed with fentry and fexit Menglong Dong
2025-12-17 10:24 ` bot+bpf-ci
2025-12-17 10:37 ` Menglong Dong
2025-12-19 0:55 ` [PATCH bpf-next v4 0/9] bpf: tracing session supporting Andrii Nakryiko
2025-12-19 1:18 ` Menglong Dong
2025-12-19 16:55 ` Andrii Nakryiko
2025-12-20 1:12 ` Menglong Dong
2025-12-20 9:01 ` Menglong Dong
2025-12-20 12:22 ` Menglong Dong
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