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. As said here all my testings with Linus Git not bpf-next. Thanks for your precious time! - Sedat -
