From: Menglong Dong <menglong8.dong@gmail.com>
To: ast@kernel.org, andrii@kernel.org
Cc: 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, davem@davemloft.net,
dsahern@kernel.org, tglx@linutronix.de, mingo@redhat.com,
jiang.biao@linux.dev, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, bpf@vger.kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH bpf-next v5 02/10] bpf: use last 8-bits for the nr_args in trampoline
Date: Wed, 24 Dec 2025 21:07:27 +0800 [thread overview]
Message-ID: <20251224130735.201422-3-dongml2@chinatelecom.cn> (raw)
In-Reply-To: <20251224130735.201422-1-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. Therefore, we use only the
last byte of ctx[-1] to store the nr_args, and reserve 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 b9714a7c3c5f..a99e286a504d 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:[~2025-12-24 13:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-24 13:07 [PATCH bpf-next v5 00/10] bpf: fsession support Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 01/10] bpf: add " Menglong Dong
2026-01-01 13:52 ` Jiri Olsa
2026-01-02 9:21 ` Menglong Dong
2026-01-02 12:11 ` Jiri Olsa
2025-12-24 13:07 ` Menglong Dong [this message]
2025-12-24 13:07 ` [PATCH bpf-next v5 03/10] bpf: add the kfunc bpf_fsession_is_return Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 04/10] bpf: add the kfunc bpf_fsession_cookie Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 05/10] bpf,x86: introduce emit_st_r0_imm64() for trampoline Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 06/10] bpf,x86: add fsession support for x86_64 Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 07/10] libbpf: add fsession support Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 08/10] selftests/bpf: add testcases for fsession Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 09/10] selftests/bpf: add testcases for fsession cookie Menglong Dong
2025-12-24 13:07 ` [PATCH bpf-next v5 10/10] selftests/bpf: test fsession mixed with fentry and fexit Menglong Dong
2026-01-02 23:21 ` [PATCH bpf-next v5 00/10] bpf: fsession support Alexei Starovoitov
2026-01-03 4:41 ` Menglong Dong
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