From: Tiezhu Yang <yangtiezhu@loongson.cn>
To: Huacai Chen <chenhuacai@kernel.org>, Hengqi Chen <hengqi.chen@gmail.com>
Cc: loongarch@lists.linux.dev, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [PATCH v1 2/3] LoongArch: BPF: Support small struct arguments for trampoline
Date: Tue, 24 Feb 2026 15:35:14 +0800 [thread overview]
Message-ID: <20260224073515.1273-3-yangtiezhu@loongson.cn> (raw)
In-Reply-To: <20260224073515.1273-1-yangtiezhu@loongson.cn>
In the current BPF code, the struct argument size is at most 16 bytes,
enforced by the verifier. According to the Procedure Call Standard for
LoongArch [1], the struct argument size below 16 bytes are provided as
part of the 8 argument registers, that is to say, the struct argument
may be passed in a pair of registers if its size is more than 8 bytes
and no more than 16 bytes.
Extend the BPF trampoline JIT to support attachment to functions that
take small structures (up to 16 bytes) as argument, save and restore
a number of "argument registers" rather than a number of arguments.
With this patch, the following related testcases passed:
sudo ./test_progs -a tracing_struct/struct_args
sudo ./test_progs -a tracing_struct/union_args
Link: https://github.com/loongson/la-abi-specs/blob/release/lapcs.adoc#structures [1]
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
arch/loongarch/net/bpf_jit.c | 55 ++++++++++++++++++++----------------
1 file changed, 31 insertions(+), 24 deletions(-)
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 98c04d6056f4..fef002bd3ffb 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1460,21 +1460,21 @@ int bpf_arch_text_invalidate(void *dst, size_t len)
return ret;
}
-static void store_args(struct jit_ctx *ctx, int nargs, int args_off)
+static void store_args(struct jit_ctx *ctx, int nregs, int args_off)
{
int i;
- for (i = 0; i < nargs; i++) {
+ for (i = 0; i < nregs; i++) {
emit_insn(ctx, std, LOONGARCH_GPR_A0 + i, LOONGARCH_GPR_FP, -args_off);
args_off -= 8;
}
}
-static void restore_args(struct jit_ctx *ctx, int nargs, int args_off)
+static void restore_args(struct jit_ctx *ctx, int nregs, int args_off)
{
int i;
- for (i = 0; i < nargs; i++) {
+ for (i = 0; i < nregs; i++) {
emit_insn(ctx, ldd, LOONGARCH_GPR_A0 + i, LOONGARCH_GPR_FP, -args_off);
args_off -= 8;
}
@@ -1590,8 +1590,8 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
void *func_addr, u32 flags)
{
int i, ret, save_ret;
- int stack_size, nargs;
- int retval_off, args_off, nargs_off, ip_off, run_ctx_off, sreg_off, tcc_ptr_off;
+ int stack_size, nregs = m->nr_args;
+ int retval_off, args_off, nregs_off, ip_off, run_ctx_off, sreg_off, tcc_ptr_off;
bool is_struct_ops = flags & BPF_TRAMP_F_INDIRECT;
void *orig_call = func_addr;
struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
@@ -1611,11 +1611,11 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
*
* FP - retval_off [ return value ] BPF_TRAMP_F_CALL_ORIG or
* BPF_TRAMP_F_RET_FENTRY_RET
- * [ argN ]
+ * [ arg regN ]
* [ ... ]
- * FP - args_off [ arg1 ]
+ * FP - args_off [ arg reg1 ]
*
- * FP - nargs_off [ regs count ]
+ * FP - nregs_off [ arg regs count ]
*
* FP - ip_off [ traced func ] BPF_TRAMP_F_IP_ARG
*
@@ -1626,15 +1626,23 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
* FP - tcc_ptr_off [ tail_call_cnt_ptr ]
*/
- if (m->nr_args > LOONGARCH_MAX_REG_ARGS)
- return -ENOTSUPP;
-
- /* FIXME: No support of struct argument */
+ /* Extra registers for struct arguments */
for (i = 0; i < m->nr_args; i++) {
- if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
- return -ENOTSUPP;
+ if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) {
+ /*
+ * The struct argument size is at most 16 bytes,
+ * enforced by the verifier. The struct argument
+ * may be passed in a pair of registers if its
+ * size is more than 8 bytes and no more than 16
+ * bytes.
+ */
+ nregs += round_up(m->arg_size[i], 8) / 8 - 1;
+ }
}
+ if (nregs > LOONGARCH_MAX_REG_ARGS)
+ return -ENOTSUPP;
+
if (flags & (BPF_TRAMP_F_ORIG_STACK | BPF_TRAMP_F_SHARE_IPMODIFY))
return -ENOTSUPP;
@@ -1648,13 +1656,12 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
retval_off = stack_size;
/* Room of trampoline frame to store args */
- nargs = m->nr_args;
- stack_size += nargs * 8;
+ stack_size += nregs * 8;
args_off = stack_size;
/* Room of trampoline frame to store args number */
stack_size += 8;
- nargs_off = stack_size;
+ nregs_off = stack_size;
/* Room of trampoline frame to store ip address */
if (flags & BPF_TRAMP_F_IP_ARG) {
@@ -1717,11 +1724,11 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
emit_insn(ctx, std, LOONGARCH_GPR_T1, LOONGARCH_GPR_FP, -ip_off);
}
- /* store nargs number */
- move_imm(ctx, LOONGARCH_GPR_T1, nargs, false);
- emit_insn(ctx, std, LOONGARCH_GPR_T1, LOONGARCH_GPR_FP, -nargs_off);
+ /* store arg regs count */
+ move_imm(ctx, LOONGARCH_GPR_T1, nregs, false);
+ emit_insn(ctx, std, LOONGARCH_GPR_T1, LOONGARCH_GPR_FP, -nregs_off);
- store_args(ctx, nargs, args_off);
+ store_args(ctx, nregs, args_off);
/* To traced function */
/* Ftrace jump skips 2 NOP instructions */
@@ -1763,7 +1770,7 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
}
if (flags & BPF_TRAMP_F_CALL_ORIG) {
- restore_args(ctx, m->nr_args, args_off);
+ restore_args(ctx, nregs, args_off);
if (flags & BPF_TRAMP_F_TAIL_CALL_CTX)
emit_insn(ctx, ldd, REG_TCC, LOONGARCH_GPR_FP, -tcc_ptr_off);
@@ -1799,7 +1806,7 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
}
if (flags & BPF_TRAMP_F_RESTORE_REGS)
- restore_args(ctx, m->nr_args, args_off);
+ restore_args(ctx, nregs, args_off);
if (save_ret) {
emit_insn(ctx, ldd, regmap[BPF_REG_0], LOONGARCH_GPR_FP, -(retval_off - 8));
--
2.42.0
next prev parent reply other threads:[~2026-02-24 7:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-24 7:35 [PATCH v1 0/3] LoongArch: BPF: Support more features for trampoline Tiezhu Yang
2026-02-24 7:35 ` [PATCH v1 1/3] LoongArch: BPF: Open code and remove invoke_bpf_mod_ret() Tiezhu Yang
2026-02-24 7:35 ` Tiezhu Yang [this message]
2026-02-24 7:35 ` [PATCH v1 3/3] LoongArch: BPF: support 12 function arguments for trampoline Tiezhu Yang
2026-02-27 9:55 ` [PATCH v1 0/3] LoongArch: BPF: Support more features " Hengqi Chen
2026-04-22 8:06 ` Huacai Chen
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