Re: [PATCH bpf-next v2 4/8] bpf, x86: refactor BPF_ST management in do_jit

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Thu Jun 4, 2026 at 1:22 PM PDT, Alexis Lothoré (eBPF Foundation) wrote:
> In order to prepare for KASAN checks insertion before every
> memory-related load or store, group all BPF_ST instructions that indeed
> access memory in a single block of fall-through cases to allow
> instrumenting those in one call, rather than having to instrument all
> cases individually.
>
> Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
> ---
>  arch/x86/net/bpf_jit_comp.c | 53 ++++++++++++++++++++++++++-------------------
>  1 file changed, 31 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 0981791014eb..943a0f315cf2 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2300,41 +2300,50 @@ static int do_jit(struct bpf_verifier_env *env, struct bpf_prog *bpf_prog, int *
>  			EMIT_LFENCE();
>  			break;
>  
> -			/* ST: *(u8*)(dst_reg + off) = imm */
>  		case BPF_ST | BPF_MEM | BPF_B:
> -			if (is_ereg(dst_reg))
> -				EMIT2(0x41, 0xC6);
> -			else
> -				EMIT1(0xC6);
> -			goto st;
>  		case BPF_ST | BPF_MEM | BPF_H:
> -			if (is_ereg(dst_reg))
> -				EMIT3(0x66, 0x41, 0xC7);
> -			else
> -				EMIT2(0x66, 0xC7);
> -			goto st;
>  		case BPF_ST | BPF_MEM | BPF_W:
> -			if (is_ereg(dst_reg))
> -				EMIT2(0x41, 0xC7);
> -			else
> -				EMIT1(0xC7);
> -			goto st;
>  		case BPF_ST | BPF_MEM | BPF_DW:
> -			if (dst_reg == BPF_REG_PARAMS && insn->off == -8) {
> -				/* Arg 6: store immediate in r9 register */
> -				emit_mov_imm64(&prog, X86_REG_R9, imm32 >> 31, (u32)imm32);
> +			switch (BPF_SIZE(insn->code)) {
> +			case BPF_B:
> +				if (is_ereg(dst_reg))
> +					EMIT2(0x41, 0xC6);
> +				else
> +					EMIT1(0xC6);
> +				break;
> +			case BPF_H:
> +				if (is_ereg(dst_reg))
> +					EMIT3(0x66, 0x41, 0xC7);
> +				else
> +					EMIT2(0x66, 0xC7);
> +				break;
> +			case BPF_W:
> +				if (is_ereg(dst_reg))
> +					EMIT2(0x41, 0xC7);
> +				else
> +					EMIT1(0xC7);
> +				break;
> +			case BPF_DW:
> +				if (dst_reg == BPF_REG_PARAMS &&
> +				    insn->off == -8) {
> +					/* Arg 6: store immediate in r9 register */
> +					emit_mov_imm64(&prog, X86_REG_R9,
> +						       imm32 >> 31, (u32)imm32);
> +					break;
> +				}
> +				EMIT2(add_1mod(0x48, dst_reg), 0xC7);

maybe it's an opportunity to cover this into separate helper function?
When indent reaches 4 tabs it's about time.