[PATCH bpf-next v3 4/6] riscv, bpf: Split prologue and epilogue into helper functions
From: Varun R Mallya
Date: Wed Jul 22 2026 - 10:25:47 EST
Split bpf_jit_build_prologue() and __build_epilogue() into helpers.
normal_stack_adjust() computes the frame size for the callee-saved
registers a program actually clobbers, emit_normal_prologue() allocates
the frame and spills those registers, and emit_normal_restore() reloads
them.
The kcfi preamble, fentry nops and tail-call-counter setup are hoisted
before the frame-size computation and they do not depend on it and the
emitted instruction sequence is unchanged.
No functional change.
Signed-off-by: Varun R Mallya <varunrmallya@xxxxxxxxx>
---
arch/riscv/net/bpf_jit_comp64.c | 152 ++++++++++++++++++--------------
1 file changed, 87 insertions(+), 65 deletions(-)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index ad089a9a4ea9..b804382075c4 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -198,9 +198,84 @@ static void emit_imm(u8 rd, s64 val, struct rv_jit_context *ctx)
emit_addi(rd, rd, lower, ctx);
}
-static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
+/* Stack space for the callee-saved registers a normal program spills,
+ * excluding the BPF stack itself.
+ */
+static int normal_stack_adjust(struct rv_jit_context *ctx)
{
- int stack_adjust = ctx->stack_size, store_offset = stack_adjust - 8;
+ int stack_adjust = 0;
+
+ if (seen_reg(RV_REG_RA, ctx))
+ stack_adjust += 8;
+ stack_adjust += 8; /* RV_REG_FP */
+ if (seen_reg(RV_REG_S1, ctx))
+ stack_adjust += 8;
+ if (seen_reg(RV_REG_S2, ctx))
+ stack_adjust += 8;
+ if (seen_reg(RV_REG_S3, ctx))
+ stack_adjust += 8;
+ if (seen_reg(RV_REG_S4, ctx))
+ stack_adjust += 8;
+ if (seen_reg(RV_REG_S5, ctx))
+ stack_adjust += 8;
+ if (ctx->arena_vm_start)
+ stack_adjust += 8;
+ stack_adjust += 8; /* RV_REG_TCC */
+
+ return round_up(stack_adjust, STACK_ALIGN);
+}
+
+/* Allocate the frame and save the callee-saved registers the program
+ * actually clobbers, then point FP at the frame top.
+ */
+static void emit_normal_prologue(struct rv_jit_context *ctx, int stack_adjust)
+{
+ int store_offset = stack_adjust - 8;
+ /* tailcall starts here, emit insn before it must be fixed */
+
+ emit_addi(RV_REG_SP, RV_REG_SP, -stack_adjust, ctx);
+
+ if (seen_reg(RV_REG_RA, ctx)) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_RA, ctx);
+ store_offset -= 8;
+ }
+ emit_sd(RV_REG_SP, store_offset, RV_REG_FP, ctx);
+ store_offset -= 8;
+ if (seen_reg(RV_REG_S1, ctx)) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_S1, ctx);
+ store_offset -= 8;
+ }
+ if (seen_reg(RV_REG_S2, ctx)) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_S2, ctx);
+ store_offset -= 8;
+ }
+ if (seen_reg(RV_REG_S3, ctx)) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_S3, ctx);
+ store_offset -= 8;
+ }
+ if (seen_reg(RV_REG_S4, ctx)) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_S4, ctx);
+ store_offset -= 8;
+ }
+ if (seen_reg(RV_REG_S5, ctx)) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_S5, ctx);
+ store_offset -= 8;
+ }
+ if (ctx->arena_vm_start) {
+ emit_sd(RV_REG_SP, store_offset, RV_REG_ARENA, ctx);
+ store_offset -= 8;
+ }
+
+ /* store TCC from RV_REG_TCC to stack */
+ emit_sd(RV_REG_SP, store_offset, RV_REG_TCC, ctx);
+ ctx->tcc_offset = store_offset;
+
+ emit_addi(RV_REG_FP, RV_REG_SP, stack_adjust, ctx);
+}
+
+static void emit_normal_restore(struct rv_jit_context *ctx, int stack_adjust)
+{
+ int store_offset = stack_adjust - 8;
if (seen_reg(RV_REG_RA, ctx)) {
emit_ld(RV_REG_RA, store_offset, RV_REG_SP, ctx);
@@ -235,6 +310,13 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
/* restore TCC from stack to RV_REG_TCC */
emit_ld(RV_REG_TCC, ctx->tcc_offset, RV_REG_SP, ctx);
+}
+
+static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
+{
+ int stack_adjust = ctx->stack_size;
+
+ emit_normal_restore(ctx, stack_adjust);
emit_addi(RV_REG_SP, RV_REG_SP, stack_adjust, ctx);
/* Set return value. */
@@ -2006,34 +2088,12 @@ 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, bpf_stack_adjust;
bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, STACK_ALIGN);
if (bpf_stack_adjust)
mark_fp(ctx);
- if (seen_reg(RV_REG_RA, ctx))
- stack_adjust += 8;
- stack_adjust += 8; /* RV_REG_FP */
- if (seen_reg(RV_REG_S1, ctx))
- stack_adjust += 8;
- if (seen_reg(RV_REG_S2, ctx))
- stack_adjust += 8;
- if (seen_reg(RV_REG_S3, ctx))
- stack_adjust += 8;
- if (seen_reg(RV_REG_S4, ctx))
- stack_adjust += 8;
- if (seen_reg(RV_REG_S5, ctx))
- stack_adjust += 8;
- if (ctx->arena_vm_start)
- stack_adjust += 8;
- stack_adjust += 8; /* RV_REG_TCC */
-
- stack_adjust = round_up(stack_adjust, STACK_ALIGN);
- stack_adjust += bpf_stack_adjust;
-
- store_offset = stack_adjust - 8;
-
/* emit kcfi type preamble immediately before the first insn */
emit_kcfi(is_subprog ? cfi_bpf_subprog_hash : cfi_bpf_hash, ctx);
@@ -2046,46 +2106,8 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx, bool is_subprog)
if (!is_subprog)
emit(rv_addi(RV_REG_TCC, RV_REG_ZERO, MAX_TAIL_CALL_CNT), ctx);
- /* tailcall starts here, emit insn before it must be fixed */
-
- emit_addi(RV_REG_SP, RV_REG_SP, -stack_adjust, ctx);
-
- if (seen_reg(RV_REG_RA, ctx)) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_RA, ctx);
- store_offset -= 8;
- }
- emit_sd(RV_REG_SP, store_offset, RV_REG_FP, ctx);
- store_offset -= 8;
- if (seen_reg(RV_REG_S1, ctx)) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_S1, ctx);
- store_offset -= 8;
- }
- if (seen_reg(RV_REG_S2, ctx)) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_S2, ctx);
- store_offset -= 8;
- }
- if (seen_reg(RV_REG_S3, ctx)) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_S3, ctx);
- store_offset -= 8;
- }
- if (seen_reg(RV_REG_S4, ctx)) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_S4, ctx);
- store_offset -= 8;
- }
- if (seen_reg(RV_REG_S5, ctx)) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_S5, ctx);
- store_offset -= 8;
- }
- if (ctx->arena_vm_start) {
- emit_sd(RV_REG_SP, store_offset, RV_REG_ARENA, ctx);
- store_offset -= 8;
- }
-
- /* store TCC from RV_REG_TCC to stack */
- emit_sd(RV_REG_SP, store_offset, RV_REG_TCC, ctx);
- ctx->tcc_offset = store_offset;
-
- emit_addi(RV_REG_FP, RV_REG_SP, stack_adjust, ctx);
+ stack_adjust = normal_stack_adjust(ctx) + bpf_stack_adjust;
+ emit_normal_prologue(ctx, stack_adjust);
if (bpf_stack_adjust)
emit_addi(RV_REG_S5, RV_REG_SP, bpf_stack_adjust, ctx);
--
2.55.0