linux-kernel - Re: [bpf-next 1/6] bpf,powerpc: Introduce bpf_jit_emit_probe_mem

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Message-ID: <e65548d0-14aa-4b9c-8051-7c91c5dffd1f@csgroup.eu>
Date: Tue, 5 Aug 2025 09:34:21 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Saket Kumar Bhaskar <skb99@...ux.ibm.com>, bpf@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: hbathini@...ux.ibm.com, sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com,
 andrii@...nel.org, eddyz87@...il.com, mykolal@...com, ast@...nel.org,
 daniel@...earbox.net, martin.lau@...ux.dev, song@...nel.org,
 yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
 sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, naveen@...nel.org,
 maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
 memxor@...il.com, iii@...ux.ibm.com, shuah@...nel.org
Subject: Re: [bpf-next 1/6] bpf,powerpc: Introduce
 bpf_jit_emit_probe_mem_store() to emit store instructions



Le 05/08/2025 à 08:27, Saket Kumar Bhaskar a écrit :
> bpf_jit_emit_probe_mem_store() is introduced to emit instructions for
> storing memory values depending on the size (byte, halfword,
> word, doubleword).

Build break with this patch

   CC      arch/powerpc/net/bpf_jit_comp64.o
arch/powerpc/net/bpf_jit_comp64.c:395:12: error: 
'bpf_jit_emit_probe_mem_store' defined but not used 
[-Werror=unused-function]
  static int bpf_jit_emit_probe_mem_store(struct codegen_context *ctx, 
u32 src_reg, s16 off,
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
make[4]: *** [scripts/Makefile.build:287: 
arch/powerpc/net/bpf_jit_comp64.o] Error 1


> 
> Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp64.c | 30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 025524378443..489de21fe3d6 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -409,6 +409,36 @@ asm (
>   "		blr				;"
>   );
>   
> +static int bpf_jit_emit_probe_mem_store(struct codegen_context *ctx, u32 src_reg, s16 off,
> +					u32 code, u32 *image)
> +{
> +	u32 tmp1_reg = bpf_to_ppc(TMP_REG_1);
> +	u32 tmp2_reg = bpf_to_ppc(TMP_REG_2);
> +
> +	switch (BPF_SIZE(code)) {
> +	case BPF_B:
> +		EMIT(PPC_RAW_STB(src_reg, tmp1_reg, off));
> +		break;
> +	case BPF_H:
> +		EMIT(PPC_RAW_STH(src_reg, tmp1_reg, off));
> +		break;
> +	case BPF_W:
> +		EMIT(PPC_RAW_STW(src_reg, tmp1_reg, off));
> +		break;
> +	case BPF_DW:
> +		if (off % 4) {
> +			EMIT(PPC_RAW_LI(tmp2_reg, off));
> +			EMIT(PPC_RAW_STDX(src_reg, tmp1_reg, tmp2_reg));
> +		} else {
> +			EMIT(PPC_RAW_STD(src_reg, tmp1_reg, off));
> +		}
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +	return 0;
> +}
> +
>   static int emit_atomic_ld_st(const struct bpf_insn insn, struct codegen_context *ctx, u32 *image)
>   {
>   	u32 code = insn.code;