> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index f3ee031edc26..9a8236d161ef 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -662,16 +662,11 @@ static void bpf_trampoline_setup_tail_call_info(u32
> *image, struct codegen_conte
> static void bpf_trampoline_restore_tail_call_cnt(u32 *image, struct
> codegen_context *ctx,
> int func_frame_offset, int
> r4_off)
> {
> - if (IS_ENABLED(CONFIG_PPC64)) {
> - /* See bpf_jit_stack_tailcallcnt() */
> - int tailcallcnt_offset = 7 * 8;
> -
> - EMIT(PPC_RAW_LL(_R3, _R1, -tailcallcnt_offset));
> - EMIT(PPC_RAW_STL(_R3, _R1, func_frame_offset -
> tailcallcnt_offset));
> - } else {
> - /* See bpf_jit_stack_offsetof() and BPF_PPC_TC */
> - EMIT(PPC_RAW_STL(_R4, _R1, r4_off));
> - }
> + /*
> + * Restore tailcall for 32-bit ppc.
> + * See bpf_jit_stack_offsetof() and BPF_PPC_TC
> + */
> + EMIT(PPC_RAW_STL(_R4, _R1, r4_off));
> }
After this change, on PPC64, the function unconditionally emits
EMIT(PPC_RAW_STL(_R4, _R1, r4_off)). However, r4_off is only assigned a value
in __arch_prepare_bpf_trampoline() when IS_ENABLED(CONFIG_PPC32), and is
initialized to 0 otherwise. Since __arch_prepare_bpf_trampoline() returns
early with -EOPNOTSUPP for PPC32, only PPC64 executes this code, meaning
r4_off will always be 0.
On PPC64, PPC_RAW_STL maps to PPC_RAW_STD. Will this emit a store of R4 to
offset 0 from R1, which is the stack back chain location? The comment says
"Restore tailcall for 32-bit ppc" but the code runs unconditionally on all
architectures.
Looking at bpf_trampoline_setup_tail_call_info() in the same file, it properly
handles the two architectures using if (IS_ENABLED(CONFIG_PPC64)). Should this
restore function have a similar guard, or return early for PPC64 since the
back propagation is no longer needed?
---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21257691486
