linux-kernel - Re: [PATCH v4 4/6] powerpc64/bpf: Add arch_bpf_stack

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Message-ID: <7a5c0997-a5d1-4a2d-8d6a-f2697f575b65@linux.ibm.com>
Date: Fri, 23 Jan 2026 18:21:46 +0530
From: Hari Bathini <hbathini@...ux.ibm.com>
To: adubey@...ux.ibm.com, bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: 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,
        christophe.leroy@...roup.eu, 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: [PATCH v4 4/6] powerpc64/bpf: Add arch_bpf_stack_walk() for BPF
 JIT



On 23/01/26 2:48 am, adubey@...ux.ibm.com wrote:
> From: Abhishek Dubey <adubey@...ux.ibm.com>
> 
> This function is used by bpf_throw() to unwind the stack
> until frame of exception-boundary during BPF exception
> handling.
> 
> This function is necessary to support BPF exceptions on
> PowerPC.
> 
> Signed-off-by: Abhishek Dubey <adubey@...ux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp64.c | 28 ++++++++++++++++++++++++++++
>   1 file changed, 28 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 18da5a866447..c25ba1ad587a 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -247,6 +247,34 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx)
>   	bpf_jit_build_fentry_stubs(image, ctx);
>   }
>   
> +void arch_bpf_stack_walk(bool (*consume_fn)(void *, u64, u64, u64), void *cookie)
> +{
> +	// callback processing always in current context
> +	unsigned long fp = current_stack_frame();
> +
> +	for (;;) {
> +		unsigned long *frame = (unsigned long *) fp;
> +		unsigned long ip;
> +
> +		if (!validate_sp(fp, current))
> +			return;
> +
> +		ip = frame[STACK_FRAME_LR_SAVE];
> +		if (!ip)
> +			break;
> +
> +		/*
> +		 * consume_fn common code expects stack pointer(sp) in third
> +		 * argument. There is no sp in ppc64, rather pass frame
> +		 * pointer.
> +		 */
> +		if (ip && !consume_fn(cookie, ip, fp, fp))
> +			break;
> +
> +		fp = frame[0];
> +	}
> +}
> +
>   int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func)
>   {
>   	unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0;

Ok. Refactoring of arch_stack_walk() & arch_bpf_stack_walk() can be done
as a follow-up, but keep the code as identical as possible. Use 'sp'
instead of 'fp' and 'stack' instead of 'frame' to make it easy to
spot the similarities. Also, a "TODO:" comment on refactoring would
be good..

- Hari