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Message-ID: <20250821140122.29752-2-yangtiezhu@loongson.cn>
Date: Thu, 21 Aug 2025 22:01:21 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
Hengqi Chen <hengqi.chen@...il.com>
Cc: loongarch@...ts.linux.dev,
bpf@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [RFC PATCH 1/2] LoongArch: BPF: Add struct arguments support for trampoline
In the current BPF code, the struct argument size is at most 16 bytes,
enforced by the verifier [1]. According to the Procedure Call Standard
for LoongArch [2], 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.
The initial aim is to pass the following related testcase:
sudo ./test_progs -a tracing_struct/struct_args
but there exist some other problems now, maybe it is related with
the following failed testcase:
sudo ./test_progs -t module_attach
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/bpf/btf.c#n7383 [1]
Link: https://github.com/loongson/la-abi-specs/blob/release/lapcs.adoc#structures [2]
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
arch/loongarch/net/bpf_jit.c | 47 ++++++++++++++++++++----------------
1 file changed, 26 insertions(+), 21 deletions(-)
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index a87f51f5b708..7bd4b132755a 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1340,21 +1340,21 @@ 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;
}
@@ -1477,8 +1477,8 @@ 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 = 0, nargs = 0;
- int retval_off, args_off, nargs_off, ip_off, run_ctx_off, sreg_off, tcc_ptr_off;
+ int stack_size = 0, 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];
@@ -1498,11 +1498,11 @@ 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
*
@@ -1516,10 +1516,16 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
if (m->nr_args > LOONGARCH_MAX_REG_ARGS)
return -ENOTSUPP;
- /* don't support struct argument */
+ /* extra regiters for struct arguments */
for (i = 0; i < m->nr_args; i++) {
- if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
- return -ENOTSUPP;
+ /*
+ * 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.
+ */
+ nr_arg_slots += round_up(m->arg_size[i], 8) / 8;
}
if (flags & (BPF_TRAMP_F_ORIG_STACK | BPF_TRAMP_F_SHARE_IPMODIFY))
@@ -1538,13 +1544,12 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
}
/* 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) {
@@ -1607,11 +1612,11 @@ 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 */
@@ -1643,7 +1648,7 @@ 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);
@@ -1680,7 +1685,7 @@ 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, LOONGARCH_GPR_A0, LOONGARCH_GPR_FP, -retval_off);
--
2.42.0
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