From: Menglong Dong <menglong8.dong@gmail.com>
To: andrii@kernel.org
Cc: ast@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, 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 v13 02/13] bpf: use the least significant byte for the nr_args in trampoline
Date: Sat, 24 Jan 2026 14:19:57 +0800 [thread overview]
Message-ID: <20260124062008.8657-3-dongml2@chinatelecom.cn> (raw)
In-Reply-To: <20260124062008.8657-1-dongml2@chinatelecom.cn>
For now, ((u64 *)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 least significant byte of ((u64 *)ctx)[-1] to store the nr_args,
and reserve the rest for other usages.
Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
---
v12:
- compute the "delta" for the BPF_FUNC_get_func_arg_cnt case
v11:
- fix the rebase conflict
v10:
- some adjustment to the subject and commit log to make the description
more precise.
v8:
- fix the missed get_func_arg_cnt
---
kernel/bpf/verifier.c | 39 +++++++++++++++++++++++----------------
kernel/trace/bpf_trace.c | 6 +++---
2 files changed, 26 insertions(+), 19 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 41bbed6418b5..2081343a848d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23747,19 +23747,21 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
/* skip 'void *__data' in btf_trace_##name() and save to reg0 */
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args - 1);
+ cnt = 1;
} else {
/* 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);
+ cnt = 2;
}
- 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[cnt++] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6);
+ insn_buf[cnt++] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3);
+ insn_buf[cnt++] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
+ insn_buf[cnt++] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_2, 0);
+ insn_buf[cnt++] = BPF_STX_MEM(BPF_DW, BPF_REG_3, BPF_REG_0, 0);
+ insn_buf[cnt++] = BPF_MOV64_IMM(BPF_REG_0, 0);
+ insn_buf[cnt++] = BPF_JMP_A(1);
+ insn_buf[cnt++] = BPF_MOV64_IMM(BPF_REG_0, -EINVAL);
new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
if (!new_prog)
@@ -23779,12 +23781,13 @@ 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;
@@ -23808,15 +23811,19 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
/* skip 'void *__data' in btf_trace_##name() and save to reg0 */
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args - 1);
+ cnt = 1;
} else {
/* 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);
+ cnt = 2;
}
- new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);
+ new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
if (!new_prog)
return -ENOMEM;
+ delta += cnt - 1;
env->prog = prog = new_prog;
insn = new_prog->insnsi + i + delta;
goto next_insn;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0e9635bcd783..d466a1503da3 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;
@@ -1231,7 +1231,7 @@ static const struct bpf_func_proto bpf_get_func_ret_proto = {
BPF_CALL_1(get_func_arg_cnt, void *, ctx)
{
/* This helper call is inlined by verifier. */
- return ((u64 *)ctx)[-1];
+ return ((u64 *)ctx)[-1] & 0xFF;
}
static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
--
2.52.0
next prev parent reply other threads:[~2026-01-24 6:20 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-24 6:19 [PATCH bpf-next v13 00/13] bpf: fsession support Menglong Dong
2026-01-24 6:19 ` [PATCH bpf-next v13 01/13] bpf: add " Menglong Dong
2026-01-24 6:19 ` Menglong Dong [this message]
2026-01-24 6:19 ` [PATCH bpf-next v13 03/13] bpf: change prototype of bpf_session_{cookie,is_return} Menglong Dong
2026-01-24 6:19 ` [PATCH bpf-next v13 04/13] bpf: support fsession for bpf_session_is_return Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 05/13] bpf: support fsession for bpf_session_cookie Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 06/13] bpf,x86: introduce emit_store_stack_imm64() for trampoline Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 07/13] bpf,x86: add fsession support for x86_64 Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 08/13] libbpf: add fsession support Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 09/13] bpftool: " Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 10/13] selftests/bpf: add testcases for fsession Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 11/13] selftests/bpf: test bpf_get_func_* " Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 12/13] selftests/bpf: add testcases for fsession cookie Menglong Dong
2026-01-24 6:20 ` [PATCH bpf-next v13 13/13] selftests/bpf: test fsession mixed with fentry and fexit Menglong Dong
2026-01-25 3:00 ` [PATCH bpf-next v13 00/13] bpf: fsession support patchwork-bot+netdevbpf
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