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

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Message-ID: <8cfa1cb2-57bf-4984-a64e-53c82440e87f@linux.ibm.com>
Date: Tue, 5 Aug 2025 17:29:47 +0530
From: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
        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, 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


On 05/08/25 1:04 pm, Christophe Leroy wrote:
>
>
> 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
>
I tried this on top of bpf-next, and for me build passed.

Note: I applied 
https://lore.kernel.org/bpf/20250717202935.29018-2-puranjay@kernel.org/ 
before applying current patch.

gcc version 14.2.1 20250110

uname -r: 6.16.0-gf2844c7fdb07

bpf-next repo: 
https://kernel.googlesource.com/pub/scm/linux/kernel/git/bpf/bpf-next

HEAD:

commit f3af62b6cee8af9f07012051874af2d2a451f0e5 (origin/master, origin/HEAD)
Author: Tao Chen <chen.dylane@...ux.dev>
Date:   Wed Jul 23 22:44:42 2025 +0800

     bpftool: Add bash completion for token argument


Build Success logs:

   TEST-OBJ [test_progs-cpuv4] xdp_vlan.test.o
   TEST-OBJ [test_progs-cpuv4] xdpwall.test.o
   TEST-OBJ [test_progs-cpuv4] xfrm_info.test.o
   BINARY   bench
   BINARY   test_maps
   BINARY   test_progs
   BINARY   test_progs-no_alu32
   BINARY   test_progs-cpuv4


Regards,

Venkat.

>
>>
>> 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;
>