On 4/11/21 11:06 PM, Sedat Dilek wrote:
On Mon, Apr 12, 2021 at 7:42 AM Yonghong Song <yhs@xxxxxx> wrote:
On 4/11/21 9:47 PM, Sedat Dilek wrote:
On Sun, Apr 11, 2021 at 9:08 PM Yonghong Song <yhs@xxxxxx> 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.
( My previous comment was from my samrtphone - so I started into my desktop. )
Thanks for your analysis and hint about inlining.
My inbox is full with that different handling of inlining "GCC vs. LLVM/Clang".
When I recall correctly and I have not to care about the inlining
optimization of clang++, then we can drop
"$(OUTPUT)/test_core_extern.skel.h" from the BPF selftests Makefile:
[ tools/testing/selftests/bpf/Makefile ]
# Make sure we are able to include and link libbpf against c++.
$(OUTPUT)/test_cpp: test_cpp.cpp $(OUTPUT)/test_core_extern.skel.h $(BPFOBJ)
$(call msg,CXX,,$@)
$(Q)$(CXX) $(CFLAGS) test_cpp.cpp $(BPFOBJ) $(LDLIBS) -o $@
Note: This is with your patchset applied against Linus Git
As we have the include here:
[ tools/testing/selftests/bpf/test_cpp.cpp ]
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
#include <iostream>
#include <bpf/libbpf.h>
#include <bpf/bpf.h>
#include <bpf/btf.h>
#include "test_core_extern.skel.h"
...
With and without keeping "test_core_extern.skel.h" I got the same
output with g++ and llvm-objdump.
Compiling with clang++ did not show that "CPP-file and C-header"
build-error when dropping "test_core_extern.skel.h" from the Makefile.
Thanks for testing. Great to see all g++/clang++ compilations passed!
As said here all my testings with Linus Git not bpf-next.
Thanks for your precious time!
- Sedat -
