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Message-ID: <20260203055231.1088479-3-dongml2@chinatelecom.cn>
Date: Tue, 3 Feb 2026 13:52:30 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: ast@...nel.org
Cc: daniel@...earbox.net,
andrii@...nel.org,
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,
bjorn@...nel.org,
pulehui@...wei.com,
puranjay@...nel.org,
pjw@...nel.org,
palmer@...belt.com,
aou@...s.berkeley.edu,
alex@...ti.fr,
jiang.biao@...ux.dev,
bpf@...r.kernel.org,
linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next 2/3] bpf, riscv: add fsession support for trampolines
Implement BPF_TRACE_FSESSION support in the RISC-V trampoline JIT. The
logic here is similar to what we did in x86_64.
In order to simply the logic, we factor out the function invoke_bpf() for
fentry and fexit.
Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
arch/riscv/net/bpf_jit_comp64.c | 74 ++++++++++++++++++++++++++++-----
1 file changed, 64 insertions(+), 10 deletions(-)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index e4f45e2e7e2f..f10418ff6a9b 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -996,6 +996,29 @@ static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_of
return ret;
}
+static int invoke_bpf(struct bpf_tramp_links *tl, int args_off, int retval_off,
+ int run_ctx_off, int func_meta_off, bool save_ret, u64 func_meta,
+ int cookie_off, struct rv_jit_context *ctx)
+{
+ int i, cur_cookie = (cookie_off - args_off) / 8;
+
+ for (i = 0; i < tl->nr_links; i++) {
+ int err;
+
+ if (tl->links[i]->link.prog->call_session_cookie) {
+ u64 meta = func_meta | ((u64)cur_cookie << BPF_TRAMP_COOKIE_INDEX_SHIFT);
+
+ emit_store_stack_imm64(RV_REG_T1, -func_meta_off, meta, ctx);
+ cur_cookie--;
+ }
+ err = invoke_bpf_prog(tl->links[i], args_off, retval_off, run_ctx_off,
+ save_ret, ctx);
+ if (err)
+ return err;
+ }
+ return 0;
+}
+
static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
const struct btf_func_model *m,
struct bpf_tramp_links *tlinks,
@@ -1005,13 +1028,15 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
int i, ret, offset;
int *branches_off = NULL;
int stack_size = 0, nr_arg_slots = 0;
- int retval_off, args_off, nregs_off, ip_off, run_ctx_off, sreg_off, stk_arg_off;
+ int retval_off, args_off, func_meta_off, ip_off, run_ctx_off, sreg_off, stk_arg_off;
+ int cookie_off, cookie_cnt;
struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
bool is_struct_ops = flags & BPF_TRAMP_F_INDIRECT;
void *orig_call = func_addr;
bool save_ret;
+ u64 func_meta;
u32 insn;
/* Two types of generated trampoline stack layout:
@@ -1042,10 +1067,14 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
* [ ... ]
* FP - args_off [ arg1 ]
*
- * FP - nregs_off [ regs count ]
+ * FP - func_meta_off [ regs count, etc ] always
*
* FP - ip_off [ traced func ] BPF_TRAMP_F_IP_ARG
*
+ * [ stack cookie N ]
+ * [ ... ]
+ * FP - cookie_off [ stack cookie 1 ]
+ *
* FP - run_ctx_off [ bpf_tramp_run_ctx ]
*
* FP - sreg_off [ callee saved reg ]
@@ -1077,14 +1106,20 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
stack_size += nr_arg_slots * 8;
args_off = stack_size;
+ /* function metadata, such as regs count */
stack_size += 8;
- nregs_off = stack_size;
+ func_meta_off = stack_size;
if (flags & BPF_TRAMP_F_IP_ARG) {
stack_size += 8;
ip_off = stack_size;
}
+ cookie_cnt = bpf_fsession_cookie_cnt(tlinks);
+ /* room for session cookies */
+ stack_size += cookie_cnt * 8;
+ cookie_off = stack_size;
+
stack_size += round_up(sizeof(struct bpf_tramp_run_ctx), 8);
run_ctx_off = stack_size;
@@ -1132,10 +1167,19 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
if (flags & BPF_TRAMP_F_IP_ARG)
emit_store_stack_imm64(RV_REG_T1, -ip_off, (u64)func_addr, ctx);
- emit_store_stack_imm64(RV_REG_T1, -nregs_off, nr_arg_slots, ctx);
+ func_meta = nr_arg_slots;
+ emit_store_stack_imm64(RV_REG_T1, -func_meta_off, func_meta, ctx);
store_args(nr_arg_slots, args_off, ctx);
+ if (bpf_fsession_cnt(tlinks)) {
+ /* clear all session cookies' value */
+ for (i = 0; i < cookie_cnt; i++)
+ emit_sd(RV_REG_FP, -cookie_off + 8 * i, RV_REG_ZERO, ctx);
+ /* clear return value to make sure fentry always get 0 */
+ emit_sd(RV_REG_FP, -retval_off, RV_REG_ZERO, ctx);
+ }
+
if (flags & BPF_TRAMP_F_CALL_ORIG) {
emit_imm(RV_REG_A0, ctx->insns ? (const s64)im : RV_MAX_COUNT_IMM, ctx);
ret = emit_call((const u64)__bpf_tramp_enter, true, ctx);
@@ -1143,9 +1187,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
return ret;
}
- for (i = 0; i < fentry->nr_links; i++) {
- ret = invoke_bpf_prog(fentry->links[i], args_off, retval_off, run_ctx_off,
- flags & BPF_TRAMP_F_RET_FENTRY_RET, ctx);
+ if (fentry->nr_links) {
+ ret = invoke_bpf(fentry, args_off, retval_off, run_ctx_off, func_meta_off,
+ flags & BPF_TRAMP_F_RET_FENTRY_RET, func_meta, cookie_off, ctx);
if (ret)
return ret;
}
@@ -1192,9 +1236,14 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
*(u32 *)(ctx->insns + branches_off[i]) = insn;
}
- for (i = 0; i < fexit->nr_links; i++) {
- ret = invoke_bpf_prog(fexit->links[i], args_off, retval_off,
- run_ctx_off, false, ctx);
+ /* set "is_return" flag for fsession */
+ func_meta |= (1ULL << BPF_TRAMP_IS_RETURN_SHIFT);
+ if (bpf_fsession_cnt(tlinks))
+ emit_store_stack_imm64(RV_REG_T1, -func_meta_off, func_meta, ctx);
+
+ if (fexit->nr_links) {
+ ret = invoke_bpf(fexit, args_off, retval_off, run_ctx_off, func_meta_off,
+ false, func_meta, cookie_off, ctx);
if (ret)
goto out;
}
@@ -2094,3 +2143,8 @@ bool bpf_jit_inlines_helper_call(s32 imm)
return false;
}
}
+
+bool bpf_jit_supports_fsession(void)
+{
+ return true;
+}
--
2.52.0
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