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Message-Id: <20251216094753.1317231-4-duanchenghao@kylinos.cn>
Date: Tue, 16 Dec 2025 17:47:52 +0800
From: Chenghao Duan <duanchenghao@...inos.cn>
To: yangtiezhu@...ngson.cn,
rostedt@...dmis.org,
mhiramat@...nel.org,
mark.rutland@....com,
hengqi.chen@...il.com,
chenhuacai@...nel.org
Cc: kernel@...0n.name,
zhangtianyang@...ngson.cn,
masahiroy@...nel.org,
linux-kernel@...r.kernel.org,
loongarch@...ts.linux.dev,
bpf@...r.kernel.org,
duanchenghao@...inos.cn,
youling.tang@...ux.dev,
jianghaoran@...inos.cn,
vincent.mc.li@...il.com,
linux-trace-kernel@...r.kernel.org
Subject: [PATCH v3 3/4] LoongArch: BPF: Enhance trampoline support for kernel and module tracing
This patch addresses two main issues in the LoongArch BPF trampoline
implementation:
1. BPF-to-BPF call handling:
- Modify the build_prologue function to ensure that the value of the
return address register ra is saved to t0 before entering the
trampoline operation.
- This ensures that the return address handling logic is accurate and
error-free when a BPF program calls another BPF program.
2. Enable Module Function Tracing Support:
- Remove the previous restrictions that blocked the tracing of kernel
module functions.
- Fix the issue that previously caused kernel lockups when attempting
to trace module functions
3. Related Function Optimizations:
- Adjust the jump offset of tail calls to ensure correct instruction
alignment.
- Enhance the bpf_arch_text_poke() function to enable accurate location
of BPF program entry points.
- Refine the trampoline return logic to ensure that the register data
is correct when returning to both the traced function and the parent
function.
After applying the current patch series, the following selftests/bpf
test cases all pass:
./test_progs -t module_attach
./test_progs -t module_fentry_shadow
./test_progs -t subprogs
./test_progs -t subprogs_extable
./test_progs -t tailcalls
./test_progs -t struct_ops -d struct_ops_multi_pages
./test_progs -t fexit_bpf2bpf
./test_progs -t fexit_stress
./test_progs -t fentry_test/fentry
./test_progs -t fexit_test/fexit
./test_progs -t fentry_fexit
./test_progs -t modify_return
./test_progs -t fexit_sleep
./test_progs -t trampoline_count
Signed-off-by: Chenghao Duan <duanchenghao@...inos.cn>
---
arch/loongarch/net/bpf_jit.c | 38 +++++++++++++++++++++++++-----------
1 file changed, 27 insertions(+), 11 deletions(-)
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 8dc58781b8eb..0c16a1b18e8f 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -139,6 +139,7 @@ static void build_prologue(struct jit_ctx *ctx)
stack_adjust = round_up(stack_adjust, 16);
stack_adjust += bpf_stack_adjust;
+ move_reg(ctx, LOONGARCH_GPR_T0, LOONGARCH_GPR_RA);
/* Reserve space for the move_imm + jirl instruction */
for (i = 0; i < LOONGARCH_LONG_JUMP_NINSNS; i++)
emit_insn(ctx, nop);
@@ -238,7 +239,7 @@ static void __build_epilogue(struct jit_ctx *ctx, bool is_tail_call)
* Call the next bpf prog and skip the first instruction
* of TCC initialization.
*/
- emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_T3, 6);
+ emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_T3, 7);
}
}
@@ -1265,7 +1266,7 @@ static int emit_jump_or_nops(void *target, void *ip, u32 *insns, bool is_call)
return 0;
}
- return emit_jump_and_link(&ctx, is_call ? LOONGARCH_GPR_T0 : LOONGARCH_GPR_ZERO, (u64)target);
+ return emit_jump_and_link(&ctx, is_call ? LOONGARCH_GPR_RA : LOONGARCH_GPR_ZERO, (u64)target);
}
static int emit_call(struct jit_ctx *ctx, u64 addr)
@@ -1289,6 +1290,10 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t,
void *new_addr)
{
int ret;
+ unsigned long size = 0;
+ unsigned long offset = 0;
+ char namebuf[KSYM_NAME_LEN];
+ void *image = NULL;
bool is_call;
u32 old_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
u32 new_insns[LOONGARCH_LONG_JUMP_NINSNS] = {[0 ... 4] = INSN_NOP};
@@ -1296,9 +1301,18 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type old_t,
/* Only poking bpf text is supported. Since kernel function entry
* is set up by ftrace, we rely on ftrace to poke kernel functions.
*/
- if (!is_bpf_text_address((unsigned long)ip))
+ if (!__bpf_address_lookup((unsigned long)ip, &size, &offset, namebuf))
return -ENOTSUPP;
+ image = ip - offset;
+ /* zero offset means we're poking bpf prog entry */
+ if (offset == 0)
+ /* skip to the nop instruction in bpf prog entry:
+ * move t0, ra
+ * nop
+ */
+ ip = image + LOONGARCH_INSN_SIZE;
+
is_call = old_t == BPF_MOD_CALL;
ret = emit_jump_or_nops(old_addr, ip, old_insns, is_call);
if (ret)
@@ -1622,14 +1636,12 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
/* To traced function */
/* Ftrace jump skips 2 NOP instructions */
- if (is_kernel_text((unsigned long)orig_call))
+ if (is_kernel_text((unsigned long)orig_call) ||
+ is_module_text_address((unsigned long)orig_call))
orig_call += LOONGARCH_FENTRY_NBYTES;
/* Direct jump skips 5 NOP instructions */
else if (is_bpf_text_address((unsigned long)orig_call))
orig_call += LOONGARCH_BPF_FENTRY_NBYTES;
- /* Module tracing not supported - cause kernel lockups */
- else if (is_module_text_address((unsigned long)orig_call))
- return -ENOTSUPP;
if (flags & BPF_TRAMP_F_CALL_ORIG) {
move_addr(ctx, LOONGARCH_GPR_A0, (const u64)im);
@@ -1722,12 +1734,16 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
emit_insn(ctx, ldd, LOONGARCH_GPR_FP, LOONGARCH_GPR_SP, 0);
emit_insn(ctx, addid, LOONGARCH_GPR_SP, LOONGARCH_GPR_SP, 16);
- if (flags & BPF_TRAMP_F_SKIP_FRAME)
+ if (flags & BPF_TRAMP_F_SKIP_FRAME) {
/* return to parent function */
- emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_RA, 0);
- else
- /* return to traced function */
+ move_reg(ctx, LOONGARCH_GPR_RA, LOONGARCH_GPR_T0);
emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_T0, 0);
+ } else {
+ /* return to traced function */
+ move_reg(ctx, LOONGARCH_GPR_T1, LOONGARCH_GPR_RA);
+ move_reg(ctx, LOONGARCH_GPR_RA, LOONGARCH_GPR_T0);
+ emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_T1, 0);
+ }
}
ret = ctx->idx;
--
2.25.1
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