On 4/24/24 14:24, Jose E. Marchesi wrote:
>
> 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?
I agree it makes sense. Will need to look for the appropriate way
to set this in gcc, but I am happy to prepare a patch.
>
>>>
>>> -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?
This is already the default. We enable -mco-re automatically in the BPF
backend if also generating BTF, unless user explicitly disables via
-mno-co-re.
This should work the same way with plain -g, once -g means BTF for the
target.
>
>>>
>>> -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@xxxxxxxxxx>
>>> Cc: Yonghong Song <yhs@xxxxxxxx>
>>> Cc: Eduard Zingerman <eddyz87@xxxxxxxxx>
>>> Cc: david.faust@xxxxxxxxxx
>>> Cc: cupertino.miranda@xxxxxxxxxx
>>> ---
>>> 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
