* [PATCH bpf-next v2 0/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT
@ 2026-08-13 7:18 Feng Jiang
2026-08-13 7:18 ` [PATCH bpf-next v2 1/2] " Feng Jiang
2026-08-13 7:18 ` [PATCH bpf-next v2 2/2] selftests/bpf: Enable stack argument tests for RV64 Feng Jiang
0 siblings, 2 replies; 6+ messages in thread
From: Feng Jiang @ 2026-08-13 7:18 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Eduard Zingerman, Kumar Kartikeya Dwivedi, Martin KaFai Lau,
Song Liu, Yonghong Song, Jiri Olsa, Emil Tsalapatis,
Ihor Solodrai, Luke Nelson, Xi Wang, Björn Töpel,
Pu Lehui, Puranjay Mohan, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Shuah Khan, Nathan Chancellor,
Nick Desaulniers, Bill Wendling, Justin Stitt
Cc: bpf, linux-riscv, linux-kernel, linux-kselftest, llvm, Feng Jiang
Port the BPF stack argument feature (BPF_REG_PARAMS / r11) to the
RV64 JIT, matching what x86 and arm64 already do.
BPF-to-BPF calls keep all extra arguments on the stack. For kfunc
calls, the JIT loads arguments 6-8 into A5-A7 at the call site to
satisfy the RISC-V C calling convention.
Tested on riscv64 QEMU with LLVM main [1]; BPF-to-BPF and kfunc
selftests pass.
[1] https://github.com/llvm/llvm-project/pull/189060
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
Changes in v2:
- Sign-extend 32-bit kfunc arguments passed on the stack (args 9+),
matching the register path and the RISC-V psABI. (Sashiko)
- Restrict the riscv selftest guard to __riscv_xlen == 64 so the
tests are not enabled on RV32. (Sashiko)
- Link to v1: https://lore.kernel.org/r/20260812-bpf-riscv-stack-args-v1-0-67b246806e59@kylinos.cn
---
Feng Jiang (2):
bpf, riscv: Add BPF stack arguments support for RV64 JIT
selftests/bpf: Enable stack argument tests for RV64
arch/riscv/net/bpf_jit.h | 1 +
arch/riscv/net/bpf_jit_comp64.c | 79 +++++++++++++++++++++-
arch/riscv/net/bpf_jit_core.c | 4 ++
.../selftests/bpf/progs/btf__stack_arg_precision.c | 3 +-
.../bpf/progs/btf__verifier_stack_arg_order.c | 3 +-
tools/testing/selftests/bpf/progs/exceptions.c | 5 +-
tools/testing/selftests/bpf/progs/stack_arg.c | 3 +-
.../testing/selftests/bpf/progs/stack_arg_kfunc.c | 3 +-
.../selftests/bpf/progs/stack_arg_precision.c | 3 +-
.../selftests/bpf/progs/verifier_stack_arg.c | 3 +-
.../selftests/bpf/progs/verifier_stack_arg_order.c | 3 +-
11 files changed, 98 insertions(+), 12 deletions(-)
---
base-commit: d114bb98936770c501c958bf2bc5fb6b7c0bad7b
change-id: 20260728-bpf-riscv-stack-args-6350d066a1e9
Best regards,
--
Feng Jiang <jiangfeng@kylinos.cn>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH bpf-next v2 1/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT
2026-08-13 7:18 [PATCH bpf-next v2 0/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT Feng Jiang
@ 2026-08-13 7:18 ` Feng Jiang
2026-08-13 8:25 ` bot+bpf-ci
2026-08-13 7:18 ` [PATCH bpf-next v2 2/2] selftests/bpf: Enable stack argument tests for RV64 Feng Jiang
1 sibling, 1 reply; 6+ messages in thread
From: Feng Jiang @ 2026-08-13 7:18 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Eduard Zingerman, Kumar Kartikeya Dwivedi, Martin KaFai Lau,
Song Liu, Yonghong Song, Jiri Olsa, Emil Tsalapatis,
Ihor Solodrai, Luke Nelson, Xi Wang, Björn Töpel,
Pu Lehui, Puranjay Mohan, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Shuah Khan, Nathan Chancellor,
Nick Desaulniers, Bill Wendling, Justin Stitt
Cc: bpf, linux-riscv, linux-kernel, linux-kselftest, llvm, Feng Jiang
Add bpf_jit_supports_stack_args() for the RV64 JIT so BPF subprograms
and kfuncs can receive more than 5 arguments via the stack
(BPF_REG_PARAMS / r11).
For BPF-to-BPF calls the caller writes outgoing arguments at the
bottom of its frame (SP-relative). The callee reads them with
FP-relative loads. Its FP is set to the caller SP in the prologue,
so the offsets match.
The RISC-V ABI puts arguments 6-8 in A5-A7 and arguments 9+ at
SP+0. Before each kfunc call, load arguments 6-8 from the outgoing
area into A5-A7 and copy any remaining arguments down so argument 9
lands at SP+0.
A5 (BPF_REG_0), A6 (TCC) and A7 are safe to clobber here: R0 is not
live before a call, TCC is backed up on the stack, and A7 is unused
by the JIT.
Limit the existing kfunc sign-extension loop to MAX_BPF_FUNC_REG_ARGS
iterations; otherwise idx >= 5 resolves to S1-S5 (BPF_R6-FP) and
corrupts callee-saved registers.
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
arch/riscv/net/bpf_jit.h | 1 +
arch/riscv/net/bpf_jit_comp64.c | 79 +++++++++++++++++++++++++++++++++++++++--
arch/riscv/net/bpf_jit_core.c | 4 +++
3 files changed, 81 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
index 419b9d795f2a..9eb4e149505d 100644
--- a/arch/riscv/net/bpf_jit.h
+++ b/arch/riscv/net/bpf_jit.h
@@ -82,6 +82,7 @@ struct rv_jit_context {
unsigned long flags;
int stack_size;
int tcc_offset;
+ u16 stack_arg_size;
u64 arena_vm_start;
u64 user_vm_start;
};
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 6b9972b07c1b..58cb3e5ff6b4 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -1815,18 +1815,43 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
const struct btf_func_model *fm;
- int idx;
+ int idx, nargs;
fm = bpf_jit_find_kfunc_model(ctx->prog, insn);
if (!fm)
return -EINVAL;
- for (idx = 0; idx < fm->nr_args; idx++) {
+ nargs = min_t(int, fm->nr_args, MAX_BPF_FUNC_REG_ARGS);
+ for (idx = 0; idx < nargs; idx++) {
u8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx);
if (fm->arg_size[idx] == sizeof(int))
emit_sextw(reg, reg, ctx);
}
+
+ /* BPF stack args -> RISC-V ABI: args 6-8 in A5-A7, 9+ at SP+0 */
+ if (fm->nr_args > MAX_BPF_FUNC_REG_ARGS) {
+ int n_stack = fm->nr_args - MAX_BPF_FUNC_REG_ARGS;
+ int n_reg = min_t(int, n_stack,
+ RV_MAX_REG_ARGS - MAX_BPF_FUNC_REG_ARGS);
+
+ for (idx = 0; idx < n_reg; idx++) {
+ int sz = fm->arg_size[MAX_BPF_FUNC_REG_ARGS + idx];
+
+ emit_ld(RV_REG_A5 + idx, idx * 8, RV_REG_SP, ctx);
+ if (sz == sizeof(int))
+ emit_sextw(RV_REG_A5 + idx, RV_REG_A5 + idx, ctx);
+ }
+
+ for (idx = n_reg; idx < n_stack; idx++) {
+ int sz = fm->arg_size[MAX_BPF_FUNC_REG_ARGS + idx];
+
+ emit_ld(RV_REG_T1, idx * 8, RV_REG_SP, ctx);
+ if (sz == sizeof(int))
+ emit_sextw(RV_REG_T1, RV_REG_T1, ctx);
+ emit_sd(RV_REG_SP, (idx - n_reg) * 8, RV_REG_T1, ctx);
+ }
+ }
}
/* restore TCC to RV_REG_TCC before bpf2bpf call */
@@ -1891,6 +1916,21 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
case BPF_LDX | BPF_MEM | BPF_H:
case BPF_LDX | BPF_MEM | BPF_W:
case BPF_LDX | BPF_MEM | BPF_DW:
+ if (insn->src_reg == BPF_REG_PARAMS) {
+ int idx = off / 8 - 1;
+
+ if (is_12b_int(idx * 8)) {
+ emit_ldx_insn(rd, idx * 8, RV_REG_FP, BPF_SIZE(code), false, ctx);
+ } else {
+ emit_imm(RV_REG_T1, idx * 8, ctx);
+ emit_add(RV_REG_T1, RV_REG_T1, RV_REG_FP, ctx);
+ emit_ldx_insn(rd, 0, RV_REG_T1, BPF_SIZE(code), false, ctx);
+ }
+ if (BPF_SIZE(code) != BPF_DW && insn_is_zext(&insn[1]))
+ return 1;
+ break;
+ }
+ fallthrough;
case BPF_LDX | BPF_PROBE_MEM | BPF_B:
case BPF_LDX | BPF_PROBE_MEM | BPF_H:
case BPF_LDX | BPF_PROBE_MEM | BPF_W:
@@ -1938,6 +1978,20 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
case BPF_ST | BPF_MEM | BPF_H:
case BPF_ST | BPF_MEM | BPF_W:
case BPF_ST | BPF_MEM | BPF_DW:
+ if (insn->dst_reg == BPF_REG_PARAMS) {
+ int idx = -off / 8 - 1;
+
+ emit_imm(RV_REG_T1, imm, ctx);
+ if (is_12b_int(idx * 8)) {
+ emit_stx_insn(RV_REG_SP, idx * 8, RV_REG_T1, BPF_SIZE(code), ctx);
+ } else {
+ emit_imm(RV_REG_T2, idx * 8, ctx);
+ emit_add(RV_REG_T2, RV_REG_SP, RV_REG_T2, ctx);
+ emit_stx_insn(RV_REG_T2, 0, RV_REG_T1, BPF_SIZE(code), ctx);
+ }
+ break;
+ }
+ fallthrough;
/* ST | PROBE_MEM32: *(size *)(dst + RV_REG_ARENA + off) = imm */
case BPF_ST | BPF_PROBE_MEM32 | BPF_B:
case BPF_ST | BPF_PROBE_MEM32 | BPF_H:
@@ -1960,6 +2014,19 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
case BPF_STX | BPF_MEM | BPF_H:
case BPF_STX | BPF_MEM | BPF_W:
case BPF_STX | BPF_MEM | BPF_DW:
+ if (insn->dst_reg == BPF_REG_PARAMS) {
+ int idx = -off / 8 - 1;
+
+ if (is_12b_int(idx * 8)) {
+ emit_stx_insn(RV_REG_SP, idx * 8, rs, BPF_SIZE(code), ctx);
+ } else {
+ emit_imm(RV_REG_T1, idx * 8, ctx);
+ emit_add(RV_REG_T1, RV_REG_SP, RV_REG_T1, ctx);
+ emit_stx_insn(RV_REG_T1, 0, rs, BPF_SIZE(code), ctx);
+ }
+ break;
+ }
+ fallthrough;
/* STX | PROBE_MEM32: *(size *)(dst + RV_REG_ARENA + off) = src */
case BPF_STX | BPF_PROBE_MEM32 | BPF_B:
case BPF_STX | BPF_PROBE_MEM32 | BPF_H:
@@ -2036,6 +2103,7 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
stack_adjust = round_up(stack_adjust, STACK_ALIGN);
stack_adjust += bpf_stack_adjust;
+ stack_adjust += ctx->stack_arg_size;
store_offset = stack_adjust - 8;
@@ -2093,7 +2161,7 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
emit_addi(RV_REG_FP, RV_REG_SP, stack_adjust, ctx);
if (bpf_stack_adjust)
- emit_addi(RV_REG_S5, RV_REG_SP, bpf_stack_adjust, ctx);
+ emit_addi(RV_REG_S5, RV_REG_SP, ctx->stack_arg_size + bpf_stack_adjust, ctx);
ctx->stack_size = stack_adjust;
@@ -2171,3 +2239,8 @@ bool bpf_jit_supports_timed_may_goto(void)
{
return true;
}
+
+bool bpf_jit_supports_stack_args(void)
+{
+ return true;
+}
diff --git a/arch/riscv/net/bpf_jit_core.c b/arch/riscv/net/bpf_jit_core.c
index cbfcd287ea16..844a0f3e0fa9 100644
--- a/arch/riscv/net/bpf_jit_core.c
+++ b/arch/riscv/net/bpf_jit_core.c
@@ -72,6 +72,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
ctx->arena_vm_start = bpf_arena_get_kern_vm_start(prog->aux->arena);
ctx->user_vm_start = bpf_arena_get_user_vm_start(prog->aux->arena);
ctx->prog = prog;
+
+ ctx->stack_arg_size = round_up(bpf_out_stack_arg_cnt(env, prog) *
+ sizeof(u64), STACK_ALIGN);
+
ctx->offset = kvzalloc_objs(int, prog->len);
if (!ctx->offset)
goto out_offset;
--
2.53.0
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH bpf-next v2 2/2] selftests/bpf: Enable stack argument tests for RV64
2026-08-13 7:18 [PATCH bpf-next v2 0/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT Feng Jiang
2026-08-13 7:18 ` [PATCH bpf-next v2 1/2] " Feng Jiang
@ 2026-08-13 7:18 ` Feng Jiang
2026-08-13 8:11 ` bot+bpf-ci
1 sibling, 1 reply; 6+ messages in thread
From: Feng Jiang @ 2026-08-13 7:18 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Eduard Zingerman, Kumar Kartikeya Dwivedi, Martin KaFai Lau,
Song Liu, Yonghong Song, Jiri Olsa, Emil Tsalapatis,
Ihor Solodrai, Luke Nelson, Xi Wang, Björn Töpel,
Pu Lehui, Puranjay Mohan, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Shuah Khan, Nathan Chancellor,
Nick Desaulniers, Bill Wendling, Justin Stitt
Cc: bpf, linux-riscv, linux-kernel, linux-kselftest, llvm, Feng Jiang
Enable the stack argument selftests for RV64. The riscv guard is
restricted to __riscv_xlen == 64 since stack arguments are only
supported by the RV64 JIT.
Keep the __BPF_FEATURE_STACK_ARGUMENT gate, defined by clang with
BPF stack argument support [1].
[1] https://github.com/llvm/llvm-project/pull/189060
Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
---
tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c | 3 ++-
tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c | 3 ++-
tools/testing/selftests/bpf/progs/exceptions.c | 5 +++--
tools/testing/selftests/bpf/progs/stack_arg.c | 3 ++-
tools/testing/selftests/bpf/progs/stack_arg_kfunc.c | 3 ++-
tools/testing/selftests/bpf/progs/stack_arg_precision.c | 3 ++-
tools/testing/selftests/bpf/progs/verifier_stack_arg.c | 3 ++-
tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c | 3 ++-
8 files changed, 17 insertions(+), 9 deletions(-)
diff --git a/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c b/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c
index 8d38aafe66a2..ab12397a9b52 100644
--- a/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c
+++ b/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c
@@ -4,7 +4,8 @@
#include <bpf/bpf_helpers.h>
#include "../test_kmods/bpf_testmod_kfunc.h"
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
long subprog_call_mem_kfunc(long a, long b, long c, long d, long e, long size)
diff --git a/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c b/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c
index 99bc115f8380..a980a3a399d3 100644
--- a/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c
+++ b/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c
@@ -3,7 +3,8 @@
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
int subprog_bad_order_6args(int a, int b, int c, int d, int e, int f)
diff --git a/tools/testing/selftests/bpf/progs/exceptions.c b/tools/testing/selftests/bpf/progs/exceptions.c
index c8d716fbd419..bae20f0f247e 100644
--- a/tools/testing/selftests/bpf/progs/exceptions.c
+++ b/tools/testing/selftests/bpf/progs/exceptions.c
@@ -379,8 +379,9 @@ int exception_bad_assert_range_with(struct __sk_buff *ctx)
return 1;
}
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) \
- && defined(__BPF_FEATURE_STACK_ARGUMENT)
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
+ defined(__BPF_FEATURE_STACK_ARGUMENT)
const volatile bool has_stack_arg = true;
diff --git a/tools/testing/selftests/bpf/progs/stack_arg.c b/tools/testing/selftests/bpf/progs/stack_arg.c
index 944e3bb603e7..3e9ed37c57bb 100644
--- a/tools/testing/selftests/bpf/progs/stack_arg.c
+++ b/tools/testing/selftests/bpf/progs/stack_arg.c
@@ -21,7 +21,8 @@ struct {
int timer_result;
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
const volatile bool has_stack_arg = true;
diff --git a/tools/testing/selftests/bpf/progs/stack_arg_kfunc.c b/tools/testing/selftests/bpf/progs/stack_arg_kfunc.c
index 345f2da2e361..b6b1a8aa7f44 100644
--- a/tools/testing/selftests/bpf/progs/stack_arg_kfunc.c
+++ b/tools/testing/selftests/bpf/progs/stack_arg_kfunc.c
@@ -6,7 +6,8 @@
#include "bpf_kfuncs.h"
#include "../test_kmods/bpf_testmod_kfunc.h"
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
const volatile bool has_stack_arg = true;
diff --git a/tools/testing/selftests/bpf/progs/stack_arg_precision.c b/tools/testing/selftests/bpf/progs/stack_arg_precision.c
index bee2eeec021d..6eebafe7f2f8 100644
--- a/tools/testing/selftests/bpf/progs/stack_arg_precision.c
+++ b/tools/testing/selftests/bpf/progs/stack_arg_precision.c
@@ -6,7 +6,8 @@
#include "../test_kmods/bpf_testmod_kfunc.h"
#include "bpf_misc.h"
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
/* Force kfunc extern BTF generation for inline asm call below.
diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
index 7e0ce5db28a0..e8cd296fe763 100644
--- a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
@@ -12,7 +12,8 @@ struct {
__type(value, long long);
} map_hash_8b SEC(".maps");
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
__noinline __used
diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
index c9fe4857da3f..562e8319ffc2 100644
--- a/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
@@ -5,7 +5,8 @@
#include <bpf/bpf_helpers.h>
#include "bpf_misc.h"
-#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
+#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
+ (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
defined(__BPF_FEATURE_STACK_ARGUMENT)
__noinline __used __naked
--
2.53.0
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next v2 2/2] selftests/bpf: Enable stack argument tests for RV64
2026-08-13 7:18 ` [PATCH bpf-next v2 2/2] selftests/bpf: Enable stack argument tests for RV64 Feng Jiang
@ 2026-08-13 8:11 ` bot+bpf-ci
0 siblings, 0 replies; 6+ messages in thread
From: bot+bpf-ci @ 2026-08-13 8:11 UTC (permalink / raw)
To: jiangfeng, ast, daniel, andrii, eddyz87, memxor, martin.lau,
song, yonghong.song, jolsa, emil, ihor.solodrai, luke.r.nels,
xi.wang, bjorn, pulehui, puranjay, pjw, palmer, aou, alex, shuah,
nathan, ndesaulniers, morbo, justinstitt
Cc: bpf, linux-riscv, linux-kernel, linux-kselftest, llvm, jiangfeng,
ast, andrii, daniel, martin.lau, eddyz87, yonghong.song, clm,
ihor.solodrai
[-- Attachment #1: Type: text/plain, Size: 2909 bytes --]
> diff --git a/tools/testing/selftests/bpf/progs/exceptions.c b/tools/testing/selftests/bpf/progs/exceptions.c
> index c8d716fbd4191..bae20f0f247eb 100644
> --- a/tools/testing/selftests/bpf/progs/exceptions.c
> +++ b/tools/testing/selftests/bpf/progs/exceptions.c
> @@ -379,8 +379,9 @@ int exception_bad_assert_range_with(struct __sk_buff *ctx)
> return 1;
> }
>
> -#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) \
> - && defined(__BPF_FEATURE_STACK_ARGUMENT)
> +#if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || \
> + (defined(__TARGET_ARCH_riscv) && __riscv_xlen == 64)) && \
> + defined(__BPF_FEATURE_STACK_ARGUMENT)
>
> const volatile bool has_stack_arg = true;
Can the code following this guard actually run on RV64?
The block enabled by this guard contains four bpf_throw()-based programs
(exception_throw_stack_arg, exception_throw_after_stack_arg,
exception_throw_subprog_stack_arg, exception_throw_subprog_after_stack_arg)
plus the has_stack_arg flag. bpf_throw is only accepted by the verifier
when the target JIT supports exceptions:
kernel/bpf/verifier.c
if (!bpf_jit_supports_exceptions()) {
RISC-V implements neither bpf_jit_supports_exceptions() nor
arch_bpf_stack_walk() (only arch/x86, arm64, s390 and powerpc do), so both
fall back to the __weak definitions in kernel/bpf/core.c:
bool __weak bpf_jit_supports_exceptions(void) { return false; }
void __weak arch_bpf_stack_walk(...) { }
Consequently exceptions.bpf.o cannot be loaded at all on RV64 - the rest
of exceptions.c is full of bpf_throw() outside this guard - and the test
is already excluded from RV64 runs:
tools/testing/selftests/bpf/DENYLIST.riscv64
# riscv64 deny list for BPF CI and local vmtest
exceptions # JIT does not support exceptions
prog_tests/exceptions.c only consumes has_stack_arg after
exceptions__load() succeeds:
ret = exceptions__load(skel);
if (!ASSERT_OK(ret, "exceptions__load"))
goto done;
...
if (skel->rodata->has_stack_arg) {
RUN_SUCCESS(exception_throw_stack_arg, 56);
so on RV64 the flag is never read. The hunk therefore changes nothing
observable on riscv64 and cannot have been validated there, which
conflicts with the commit subject 'Enable the stack argument selftests for
RV64'. The other seven hunks are genuinely effective; only this one is
not.
Either drop the exceptions.c hunk from this patch (and add it when the
RV64 JIT gains arch_bpf_stack_walk()/bpf_jit_supports_exceptions()), or
state in the changelog that it is deliberately pre-enabled for a future
RV64 exception implementation and remains untested for now.
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31677823910
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next v2 1/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT
2026-08-13 7:18 ` [PATCH bpf-next v2 1/2] " Feng Jiang
@ 2026-08-13 8:25 ` bot+bpf-ci
2026-08-13 11:35 ` Feng Jiang
0 siblings, 1 reply; 6+ messages in thread
From: bot+bpf-ci @ 2026-08-13 8:25 UTC (permalink / raw)
To: jiangfeng, ast, daniel, andrii, eddyz87, memxor, martin.lau,
song, yonghong.song, jolsa, emil, ihor.solodrai, luke.r.nels,
xi.wang, bjorn, pulehui, puranjay, pjw, palmer, aou, alex, shuah,
nathan, ndesaulniers, morbo, justinstitt
Cc: bpf, linux-riscv, linux-kernel, linux-kselftest, llvm, jiangfeng,
ast, andrii, daniel, martin.lau, eddyz87, yonghong.song, clm,
ihor.solodrai
[-- Attachment #1: Type: text/plain, Size: 1904 bytes --]
> bpf, riscv: Add BPF stack arguments support for RV64 JIT
>
> Add bpf_jit_supports_stack_args() for the RV64 JIT so BPF subprograms
> and kfuncs can receive more than 5 arguments via the stack
> (BPF_REG_PARAMS / r11).
>
> For BPF-to-BPF calls the caller writes outgoing arguments at the
> bottom of its frame (SP-relative). The callee reads them with
> FP-relative loads. Its FP is set to the caller SP in the prologue,
> so the offsets match.
>
> The RISC-V ABI puts arguments 6-8 in A5-A7 and arguments 9+ at
> SP+0. Before each kfunc call, load arguments 6-8 from the outgoing
> area into A5-A7 and copy any remaining arguments down so argument 9
> lands at SP+0.
>
> A5 (BPF_REG_0), A6 (TCC) and A7 are safe to clobber here: R0 is not
> live before a call, TCC is backed up on the stack, and A7 is unused
> by the JIT.
>
> Limit the existing kfunc sign-extension loop to MAX_BPF_FUNC_REG_ARGS
> iterations; otherwise idx >= 5 resolves to S1-S5 (BPF_R6-FP) and
> corrupts callee-saved registers.
>
> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
This looks like a bug fix for stack argument support. The commit message
describes how the sign-extension loop was limited to prevent corruption
of callee-saved registers S1-S5 when idx >= 5. This fixes an issue
introduced by commit 443574b03387 ("riscv, bpf: Fix kfunc parameters
incompatibility between bpf and riscv abi"), which added the
sign-extension loop without limiting it to MAX_BPF_FUNC_REG_ARGS.
Should this include:
Fixes: 443574b03387 ("riscv, bpf: Fix kfunc parameters incompatibility between bpf and riscv abi")
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31677823910
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH bpf-next v2 1/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT
2026-08-13 8:25 ` bot+bpf-ci
@ 2026-08-13 11:35 ` Feng Jiang
0 siblings, 0 replies; 6+ messages in thread
From: Feng Jiang @ 2026-08-13 11:35 UTC (permalink / raw)
To: bot+bpf-ci, ast, daniel, andrii, eddyz87, memxor, martin.lau,
song, yonghong.song, jolsa, emil, ihor.solodrai, luke.r.nels,
xi.wang, bjorn, pulehui, puranjay, pjw, palmer, aou, alex, shuah,
nathan, ndesaulniers, morbo, justinstitt
Cc: bpf, linux-riscv, linux-kernel, linux-kselftest, llvm, martin.lau, clm
On 2026/8/13 16:25, bot+bpf-ci@kernel.org wrote:
>> bpf, riscv: Add BPF stack arguments support for RV64 JIT
>>
>> Add bpf_jit_supports_stack_args() for the RV64 JIT so BPF subprograms
>> and kfuncs can receive more than 5 arguments via the stack
>> (BPF_REG_PARAMS / r11).
>>
>> For BPF-to-BPF calls the caller writes outgoing arguments at the
>> bottom of its frame (SP-relative). The callee reads them with
>> FP-relative loads. Its FP is set to the caller SP in the prologue,
>> so the offsets match.
>>
>> The RISC-V ABI puts arguments 6-8 in A5-A7 and arguments 9+ at
>> SP+0. Before each kfunc call, load arguments 6-8 from the outgoing
>> area into A5-A7 and copy any remaining arguments down so argument 9
>> lands at SP+0.
>>
>> A5 (BPF_REG_0), A6 (TCC) and A7 are safe to clobber here: R0 is not
>> live before a call, TCC is backed up on the stack, and A7 is unused
>> by the JIT.
>>
>> Limit the existing kfunc sign-extension loop to MAX_BPF_FUNC_REG_ARGS
>> iterations; otherwise idx >= 5 resolves to S1-S5 (BPF_R6-FP) and
>> corrupts callee-saved registers.
>>
>> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
>
> This looks like a bug fix for stack argument support. The commit message
> describes how the sign-extension loop was limited to prevent corruption
> of callee-saved registers S1-S5 when idx >= 5. This fixes an issue
> introduced by commit 443574b03387 ("riscv, bpf: Fix kfunc parameters
> incompatibility between bpf and riscv abi"), which added the
> sign-extension loop without limiting it to MAX_BPF_FUNC_REG_ARGS.
>
> Should this include:
>
> Fixes: 443574b03387 ("riscv, bpf: Fix kfunc parameters incompatibility between bpf and riscv abi")
>
No Fixes: tag. When 443574b03387 added the loop, the verifier still
unconditionally rejected kfuncs with more than 5 args, so fm->nr_args
was always <= 5 and the loop never touched S1-S5. The corruption is
only reachable once this series enables stack arguments, so bounding
the loop is part of the feature, not a fix for a triggerable bug.
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/3167782391
--
With Best Regards,
Feng Jiang
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2026-08-13 11:35 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-08-13 7:18 [PATCH bpf-next v2 0/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT Feng Jiang
2026-08-13 7:18 ` [PATCH bpf-next v2 1/2] " Feng Jiang
2026-08-13 8:25 ` bot+bpf-ci
2026-08-13 11:35 ` Feng Jiang
2026-08-13 7:18 ` [PATCH bpf-next v2 2/2] selftests/bpf: Enable stack argument tests for RV64 Feng Jiang
2026-08-13 8:11 ` bot+bpf-ci
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