[PATCH bpf-next v4 2/3] riscv, bpf: Add BPF stack arguments support for RV64 JIT
From: Pu Lehui
Date: Sat Sep 05 2026 - 02:59:20 EST
From: Feng Jiang <jiangfeng@xxxxxxxxxx>
Implement bpf_jit_supports_stack_args() on RV64 JIT to allow bpf
subprogs and kfuncs to pass and receive more than 5 arguments.
In the riscv abi, the first 8 arguments are passed in registers a0 to
a7, and arguments 9+ reside on the stack. To align bpf stack arguments
with this calling convention and unify bpf2bpf calls with kfuncs, map
the first 3 bpf stack arguments (6th to 8th) directly to a5 to a7, and
store or load the remaining arguments (9th+) at SP or FP. Reserve
outgoing stack space in the prologue accordingly when stack_arg_cnt
exceeds 3.
In addition, update kfunc argument sign extension to handle all 8
register arguments as well as any arguments passed on the stack.
Co-developed-by: Pu Lehui <pulehui@xxxxxxxxxx>
Signed-off-by: Feng Jiang <jiangfeng@xxxxxxxxxx>
Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
---
arch/riscv/net/bpf_jit.h | 1 +
arch/riscv/net/bpf_jit_comp64.c | 79 +++++++++++++++++++++++++++++----
arch/riscv/net/bpf_jit_core.c | 6 +++
3 files changed, 77 insertions(+), 9 deletions(-)
diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
index 419b9d795f2a..039877f286fc 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;
+ int stack_arg_sz;
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 aac128b9f0a4..cda99c1f9ffe 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -498,6 +498,18 @@ static void emit_ldx(u8 rd, s16 off, u8 rs, u8 size, bool sign_ext,
ctx->ex_jmp_off = ctx->ninsns;
}
+static void emit_stack_arg_ldx(u8 rd, s16 off, struct rv_jit_context *ctx)
+{
+ int idx = off / 8 - 1;
+
+ if (idx < 3) {
+ emit_mv(rd, RV_REG_A5 + idx, ctx);
+ return;
+ }
+
+ emit_ldx_insn(rd, (idx - 3) * 8, RV_REG_FP, BPF_DW, false, ctx);
+}
+
static void emit_st(u8 rd, s16 off, s32 imm, u8 size, struct rv_jit_context *ctx)
{
emit_imm(RV_REG_T1, imm, ctx);
@@ -515,6 +527,19 @@ static void emit_st(u8 rd, s16 off, s32 imm, u8 size, struct rv_jit_context *ctx
ctx->ex_jmp_off = ctx->ninsns;
}
+static void emit_stack_arg_st(s16 off, s32 imm, struct rv_jit_context *ctx)
+{
+ int idx = -off / 8 - 1;
+
+ emit_imm(RV_REG_T1, imm, ctx);
+ if (idx < 3) {
+ emit_mv(RV_REG_A5 + idx, RV_REG_T1, ctx);
+ return;
+ }
+
+ emit_stx_insn(RV_REG_SP, (idx - 3) * 8, RV_REG_T1, BPF_DW, ctx);
+}
+
static void emit_stx(u8 rd, s16 off, u8 rs, u8 size, struct rv_jit_context *ctx)
{
if (is_12b_int(off)) {
@@ -531,6 +556,18 @@ static void emit_stx(u8 rd, s16 off, u8 rs, u8 size, struct rv_jit_context *ctx)
ctx->ex_jmp_off = ctx->ninsns;
}
+static void emit_stack_arg_stx(s16 off, u8 rs, struct rv_jit_context *ctx)
+{
+ int idx = -off / 8 - 1;
+
+ if (idx < 3) {
+ emit_mv(RV_REG_A5 + idx, rs, ctx);
+ return;
+ }
+
+ emit_stx_insn(RV_REG_SP, (idx - 3) * 8, rs, BPF_DW, ctx);
+}
+
static int emit_atomic_ld_st(u8 rd, u8 rs, const struct bpf_insn *insn,
struct rv_jit_context *ctx)
{
@@ -1824,11 +1861,21 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
return -EINVAL;
for (idx = 0; idx < fm->nr_args; idx++) {
- u8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx);
bool sign = fm->arg_flags[idx] & BTF_FMODEL_SIGNED_ARG;
-
- if (sign_extend(reg, reg, fm->arg_size[idx], sign, ctx))
- return -EINVAL;
+ u8 arg_sz = fm->arg_size[idx];
+
+ if (arg_sz == 8 || (arg_sz != 4 && !sign))
+ continue;
+
+ if (idx < RV_MAX_REG_ARGS) {
+ if (sign_extend(RV_REG_A0 + idx, RV_REG_A0 + idx, arg_sz, sign, ctx))
+ return -EINVAL;
+ } else {
+ emit_ld(RV_REG_T1, (idx - RV_MAX_REG_ARGS) * 8, RV_REG_SP, ctx);
+ if (sign_extend(RV_REG_T1, RV_REG_T1, arg_sz, sign, ctx))
+ return -EINVAL;
+ emit_sd(RV_REG_SP, (idx - RV_MAX_REG_ARGS) * 8, RV_REG_T1, ctx);
+ }
}
}
@@ -1927,7 +1974,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
rs = RV_REG_T2;
}
- emit_ldx(rd, off, rs, BPF_SIZE(code), sign_ext, ctx);
+ if (is_stack_arg_ldx(insn))
+ emit_stack_arg_ldx(rd, off, ctx);
+ else
+ emit_ldx(rd, off, rs, BPF_SIZE(code), sign_ext, ctx);
ret = add_exception_handler(insn, rd, ctx);
if (ret)
@@ -1957,7 +2007,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
rd = RV_REG_T3;
}
- emit_st(rd, off, imm, BPF_SIZE(code), ctx);
+ if (is_stack_arg_st(insn))
+ emit_stack_arg_st(off, imm, ctx);
+ else
+ emit_st(rd, off, imm, BPF_SIZE(code), ctx);
ret = add_exception_handler(insn, REG_DONT_CLEAR_MARKER, ctx);
if (ret)
@@ -1979,7 +2032,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
rd = RV_REG_T2;
}
- emit_stx(rd, off, rs, BPF_SIZE(code), ctx);
+ if (is_stack_arg_stx(insn))
+ emit_stack_arg_stx(off, rs, ctx);
+ else
+ emit_stx(rd, off, rs, BPF_SIZE(code), ctx);
ret = add_exception_handler(insn, REG_DONT_CLEAR_MARKER, ctx);
if (ret)
@@ -2029,9 +2085,9 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
{
- int i, stack_adjust = 0, store_offset, bpf_stack_adjust;
+ int i, stack_adjust = 0, store_offset, bpf_stack_adjust = ctx->stack_arg_sz;
- bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, STACK_ALIGN);
+ bpf_stack_adjust += round_up(ctx->prog->aux->stack_depth, STACK_ALIGN);
if (bpf_stack_adjust)
mark_fp(ctx);
@@ -2190,3 +2246,8 @@ 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..ed48005568c8 100644
--- a/arch/riscv/net/bpf_jit_core.c
+++ b/arch/riscv/net/bpf_jit_core.c
@@ -48,6 +48,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_pr
int pass = 0, prev_ninsns = 0, i;
struct rv_jit_data *jit_data;
struct rv_jit_context *ctx;
+ u16 stack_arg_cnt;
if (!prog->jit_requested)
return prog;
@@ -71,6 +72,11 @@ 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);
+
+ stack_arg_cnt = bpf_out_stack_arg_cnt(env, prog);
+ /* First 3 stack args in regs, rest on stack */
+ ctx->stack_arg_sz = stack_arg_cnt > 3 ? round_up((stack_arg_cnt - 3) * 8, STACK_ALIGN) : 0;
+
ctx->prog = prog;
ctx->offset = kvzalloc_objs(int, prog->len);
if (!ctx->offset)
--
2.34.1