From: Yonghong Song <yhs@fb.com>
To: <sedat.dilek@gmail.com>
Cc: <bpf@vger.kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
<kernel-team@fb.com>, Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH bpf-next 3/5] selftests/bpf: fix test_cpp compilation failure with clang
Date: Sun, 11 Apr 2021 22:42:31 -0700 [thread overview]
Message-ID: <1184be32-46d6-15a8-06b6-7e9bd26a88c6@fb.com> (raw)
In-Reply-To: <CA+icZUVPQT9WNona7xdmZP+2nS=xLn6hssd1wmLSeVNBzsOqTQ@mail.gmail.com>
On 4/11/21 9:47 PM, Sedat Dilek wrote:
> On Sun, Apr 11, 2021 at 9:08 PM Yonghong Song <yhs@fb.com> wrote:
> [ ... ]
>>> BTW, did you check (llvm-)objdump output?
>>>
>>> $ /opt/llvm-toolchain/bin/llvm-objdump-12 -Dr test_cpp | grep core_extern
>>
>> This is what I got with g++ compiled test_cpp:
>>
>> $ llvm-objdump -Dr test_cpp | grep core_extern
>> 406a80: e8 5b 01 00 00 callq 0x406be0
>> <_ZL25test_core_extern__destroyP16test_core_extern>
>> 406ab9: e8 22 01 00 00 callq 0x406be0
>> <_ZL25test_core_extern__destroyP16test_core_extern>
>> 0000000000406be0 <_ZL25test_core_extern__destroyP16test_core_extern>:
>> 406be3: 74 1a je 0x406bff
>> <_ZL25test_core_extern__destroyP16test_core_extern+0x1f>
>> 406bef: 74 05 je 0x406bf6
>> <_ZL25test_core_extern__destroyP16test_core_extern+0x16>
>>
>
> What is the output when compiling with clang++ in your bpf-next environment?
$ llvm-objdump -Dr test_cpp | grep core_extern
$
So looks like all test_core_extern_*() functions are inlined.
This can be confirmed by looking at assembly code.
while for gcc, there is still the call to
_ZL25test_core_extern__destroyP16test_core_extern
which is
test_core_extern__destroy(test_core_extern*)
This is just a difference between compiler optimizations
between gcc and clang. We don't need to worry about this.
>
> - Sedat -
>
next prev parent reply other threads:[~2021-04-12 5:42 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-10 16:49 [PATCH bpf-next 0/5] support build selftests/bpf with clang Yonghong Song
2021-04-10 16:49 ` [PATCH bpf-next 1/5] selftests: set CC to clang in lib.mk if LLVM is set Yonghong Song
2021-04-11 10:22 ` Sedat Dilek
2021-04-11 16:51 ` Yonghong Song
2021-04-11 17:10 ` Sedat Dilek
2021-04-10 16:49 ` [PATCH bpf-next 2/5] tools: allow proper CC/CXX/... override with LLVM=1 in Makefile.include Yonghong Song
2021-04-11 10:24 ` Sedat Dilek
2021-04-11 16:52 ` Yonghong Song
2021-04-10 16:49 ` [PATCH bpf-next 3/5] selftests/bpf: fix test_cpp compilation failure with clang Yonghong Song
2021-04-11 10:47 ` Sedat Dilek
2021-04-11 17:20 ` Yonghong Song
2021-04-11 17:31 ` Sedat Dilek
2021-04-11 19:08 ` Yonghong Song
2021-04-12 4:47 ` Sedat Dilek
2021-04-12 5:42 ` Yonghong Song [this message]
2021-04-12 6:06 ` Sedat Dilek
2021-04-12 14:15 ` Yonghong Song
2021-04-13 4:32 ` Andrii Nakryiko
2021-04-13 6:12 ` Yonghong Song
2021-04-13 17:50 ` Andrii Nakryiko
2021-04-10 16:49 ` [PATCH bpf-next 4/5] selftests/bpf: silence clang compilation warnings Yonghong Song
2021-04-11 11:12 ` Sedat Dilek
2021-04-11 17:40 ` Yonghong Song
2021-04-10 16:49 ` [PATCH bpf-next 5/5] bpftool: fix a clang compilation warning Yonghong Song
2021-04-11 11:05 ` Sedat Dilek
2021-04-11 17:24 ` Yonghong Song
2021-04-10 17:23 ` [PATCH bpf-next 0/5] support build selftests/bpf with clang Alexei Starovoitov
2021-04-10 17:38 ` Yonghong Song
2021-04-10 19:19 ` Sedat Dilek
2021-04-11 16:46 ` Yonghong Song
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