Re: [PATCH bpf-next v9 4/5] bpf, x86: Emit ENDBR for indirect jump targets

[Leon Hwang]

On 2026/3/14 14:48, Xu Kuohai wrote:
> On 3/13/2026 6:15 PM, Leon Hwang wrote:
>>> +#ifdef CONFIG_X86_KERNEL_IBT
>>> +        if (bpf_insn_is_indirect_target(env, bpf_prog, i - 1))
>>> +            EMIT_ENDBR();
>>> +#endif
>> NIT: is this CONFIG check necessary?
>>
>> EMIT_ENDBR already checks it.
>>
>> #ifdef CONFIG_X86_KERNEL_IBT
>> #define EMIT_ENDBR()        EMIT(gen_endbr(), 4)
>> #define EMIT_ENDBR_POISON()    EMIT(gen_endbr_poison(), 4)
>> #else
>> #define EMIT_ENDBR()
>> #define EMIT_ENDBR_POISON()
>> #endif
> 
> Well, the code was originally written exactly without the #ifdef, but it
> triggered
> -Wempty-body warning: https://lore.kernel.org/bpf/202603051414.AAMjmOHv-
> lkp@xxxxxxxxx/.
> 

Let's update the macros instead, which can avoid the build warning and
get rid of the CONFIG check as well.

#define EMIT_ENDBR() do { } while (0)
#define EMIT_ENDBR_POISON() do { } while (0)

The way of "do { } while (0)" is commonly used in kernel.

Thanks,
Leon