Re: [PATCH bpf-next] bpf: add a few more options for GCC_BPF in selftests/bpf/Makefile

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

Hi Yonghong.

> On 4/24/24 1:41 AM, Jose E. Marchesi wrote:
>> This little patch modifies selftests/bpf/Makefile so it passes the
>> following extra options when invoking gcc-bpf:
>>
>>   -gbtf
>>     This makes GCC to emit BTF debug info in .BTF and .BTF.ext.
>
> Could we do if '-g' is specified, for bpf program,
> btf will be automatically generated?

Hmm, in principle I wouldn't oppose for -g to mean -gbtf instead of
-gdwarf.  DWARF can always be generated by using -gdwarf.

Faust, Indu, WDYT?

>>
>>   -mco-re
>>     This tells GCC to generate CO-RE relocations in .BTF.ext.
>
> Can we make this default? That is, remove -mco-re option. I
> can imagine for any serious bpf program, co-re is a must.

CO-RE depends on BTF.  So I understand the above as making -mco-re the
default if BTF is generated, i.e. if -gbtf (or -g with the modification
above) are specified.  Isn't that what clang does?  Am I interpreting
correctly?

>>
>>   -masm=pseudoc
>>     This tells GCC to emit BPF assembler using the pseudo-c syntax.
>
> Can we make it the other way round such that -masm=pseudoc is
> the default? You can have an option e.g., -masm=non-pseudoc,
> for the other format?

We could add a configure-time build option:

  --with-bpf-default-asm-syntax={pseudoc,normal}

so that GCC can be built to use whatever selected syntax as default.
Distros and people can then decide what to do.

>>
>> Tested in bpf-next master.
>> No regressions.
>>
>> Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
>> Cc: Yonghong Song <yhs@meta.com>
>> Cc: Eduard Zingerman <eddyz87@gmail.com>
>> Cc: david.faust@oracle.com
>> Cc: cupertino.miranda@oracle.com
>> ---
>>   tools/testing/selftests/bpf/Makefile | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index edc73f8f5aef..702428021132 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -442,7 +442,7 @@ endef
>>   # Build BPF object using GCC
>>   define GCC_BPF_BUILD_RULE
>>   	$(call msg,GCC-BPF,$(TRUNNER_BINARY),$2)
>> -	$(Q)$(BPF_GCC) $3 -O2 -c $1 -o $2
>> +	$(Q)$(BPF_GCC) $3 -O2 -gbtf -mco-re -masm=pseudoc -c $1 -o $2
>>   endef
>>     SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c