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Message-ID: <20260123073532.238985-3-dongml2@chinatelecom.cn>
Date: Fri, 23 Jan 2026 15:35:22 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: andrii@...nel.org
Cc: daniel@...earbox.net,
martin.lau@...ux.dev,
eddyz87@...il.com,
song@...nel.org,
yonghong.song@...ux.dev,
john.fastabend@...il.com,
kpsingh@...nel.org,
sdf@...ichev.me,
haoluo@...gle.com,
jolsa@...nel.org,
davem@...emloft.net,
dsahern@...nel.org,
tglx@...utronix.de,
mingo@...hat.com,
jiang.biao@...ux.dev,
bp@...en8.de,
dave.hansen@...ux.intel.com,
x86@...nel.org,
hpa@...or.com,
bpf@...r.kernel.org,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v11 02/12] bpf: use the least significant byte for the nr_args in trampoline
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@...natelecom.cn>
---
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 | 38 ++++++++++++++++++++++----------------
kernel/trace/bpf_trace.c | 6 +++---
2 files changed, 25 insertions(+), 19 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 41bbed6418b5..b3f912ad18ba 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;
@@ -23808,12 +23811,15 @@ 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;
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
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