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

[Xu Kuohai]

On 3/14/2026 9:35 PM, Leon Hwang wrote:
> 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 at intel.com/.
>>
> 
> 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.
>

Sorry for the delay. This makes sense to me. The code looks much cleaner
without the #ifdef, thanks!

> Thanks,
> Leon