Re: [COMMITTED] bpf: define __bpf__ as well as __BPF__ as a target macro

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

> On Mon, Aug 29, 2022 at 1:16 PM Jose E. Marchesi via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>>
>> LLVM defines both __bpf__ and __BPF_ as target macros.
>> GCC was defining only __BPF__.
>>
>> This patch defines __bpf__ as a target macro for BPF.
>> Tested in bpf-unknown-none.
>>
>> gcc/ChangeLog:
>>
>>         * config/bpf/bpf.cc (bpf_target_macros): Define __bpf__ as a
>>         target macro.
>> ---
>>  gcc/config/bpf/bpf.cc | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
>> index 7e37e080808..9cb56cfb287 100644
>> --- a/gcc/config/bpf/bpf.cc
>> +++ b/gcc/config/bpf/bpf.cc
>> @@ -291,6 +291,7 @@ void
>>  bpf_target_macros (cpp_reader *pfile)
>>  {
>>    builtin_define ("__BPF__");
>> +  builtin_define ("__bpf__");
>>
>>    if (TARGET_BIG_ENDIAN)
>>      builtin_define ("__BPF_BIG_ENDIAN__");
>> --
>> 2.30.2
>>
>
> Having multiple choices in this case seems to just add confusion to
> users and making code search slightly more inconvenient.
>
> How much code uses LLVM specific __bpf__? Can it be migrated? Should
> LLVM undefine the macro instead?

I agree that it would be better to support just one form of the target
macro.  Having two alternative forms can only lead to problems.

But I think the train left the station long ago to do any better: there
are files in the kernel tree that rely on __bpf__ and there may be BPF
programs around doing the same thing.