Re: [PATCH bpf-next v3 4/6] riscv, bpf: Split prologue and epilogue into helper functions

Hi Varun,

looks good to me, but some real small nits.

On 2026/7/22 22:00, Varun R Mallya wrote:
> 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 <[email protected]>
> ---
>   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);
>   }
>   

pls use the following comment format:

/*
  * xxx
  */

or

/* xxx */

> -static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
> +/* Stack space for the callee-saved registers a normal program spills,

how about, the registers based strictly on what is seen in the bpf prog.

> + * 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)

prefer to let ctx as last param, and the following pls make a change.

> +{
> +	int store_offset = stack_adjust - 8;
> +	/* tailcall starts here, emit insn before it must be fixed */

remove this comment.

> +
> +	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 */

keep this comment here.

> -
> -	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);