linux-kernel - Re: [PATCH v2 4/6] powerpc64/bpf: Add arch_bpf_stack

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Message-ID: <18dacad3-ec1d-4c91-adfb-2ee8d592de29@kernel.org>
Date: Wed, 14 Jan 2026 13:37:50 +0100
From: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
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: 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: [PATCH v2 4/6] powerpc64/bpf: Add arch_bpf_stack_walk() for BPF
 JIT



Le 14/01/2026 à 12:44, adubey@...ux.ibm.com a écrit :
> 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 cebf81fbd59f..ec58395f74f7 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];
> +	}
> +}
> +

This fonction looks very close to arch_stack_walk(). Would it be 
possible to refactor and have a common part used by both functions, like 
ARM64 for instance ?

>   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;