Re: [PATCH v4 4/6] powerpc64/bpf: Add arch_bpf_stack_walk() for BPF JIT

Hari Bathini
2026-01-23T12:53:37Z

On 23/01/26 2:48 am, adubey@linux.ibm.com wrote:
> From: Abhishek Dubey <adubey@linux.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@linux.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