[Bug c++/104712] -fkeep-inline-functions causing link errors (debian but not godbolt?)

[ajrh at ajrh dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104712

ajrh at ajrh dot net changed:

   What|Removed |Added

 CC||ajrh at ajrh dot net

--- Comment #6 from ajrh at ajrh dot net ---
Created attachment 52525
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52525=edit
mention -ffunction-sections -Wl,-gc-sections in gcov manual

On deeper investigation the original code had lots of unused inlined explicit
template specializations, and a few of these had constants missing the 'inline'
keyword.   So gcc is behaving perfectly.Apologies for the misleading
testcase.

I understand better now:--keep-inline-functions is  correctly generating
lots of otherwise dead code,  and of course some of it might not link.   
Though I only wanted to link it in order to run gcov to find and remove all the
dead code, an amusing catch-22.

Am I correct that a good way to fix this sometimes will be to use
-ffunction-sections -Wl,-gc-sections ?E.g. in the example below:



extern int i;

inline int f(const char *x)
{
return i;
}

int main(int argc, char *argv[])
{
return !!argc;
}



 gcc -o x --coverage x.cpp && {x; gcov x}
File 'x.cpp'
Lines executed:100.00% of 2

gcc -o x --coverage -fkeep-inline-functions x.cpp && {x; gcov x}
x.cpp:(.text._Z1fPKc[_Z1fPKc]+0x1c): undefined reference to `i'

g++ -o x --coverage -fkeep-inline-functions -ffunction-sections
-Wl,-gc-sections x.cpp && {x; gcov x} 
File 'x.cpp'
Lines executed:50.00% of 4



If that's right it might be useful to  mention as a hint in the manual.   
Attached a texi patch if so.

Thank you all for the help.

[Bug c++/104712] -fkeep-inline-functions causing link errors (debian but not godbolt?)

[ajrh at ajrh dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104712

--- Comment #2 from ajrh at ajrh dot net ---
Oh drat,  reduced test cases are maddening...  it's an inline static const in
my original.   I'll try to reduce something again.

[Bug c++/104712] New: -fkeep-inline-functions causing link errors (debian but not godbolt?)

[ajrh at ajrh dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104712

Bug ID: 104712
   Summary: -fkeep-inline-functions causing link errors  (debian
but not godbolt?)
   Product: gcc
   Version: 11.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: ajrh at ajrh dot net
  Target Milestone: ---

For use with gcov, I'm trying to use the --keep-inline-functions flag, as
suggested in the GCC manual,  but it's causing a lot of link errors on various
types of objects.   The undefined references were my initial problem,  I'm not
sure about the relocation errors also.

Possibly it's config-specific, as I made one example via creduce, which gives
the error below,  but it appears to compile fine in godbolt.Debian config
attached below also.



template  void g(T, T) { }

class C {
  static int XYZZY;
  int x;
  void f() { g(x, XYZZY); }
};

int main()
{
return 0;
}



This compiles and runs cleanly with 'g++ -Wall foo.cpp && a.out'

But with the flag added:

g++ -Wall -fkeep-inline-functions foo.cpp

/usr/bin/ld: /tmp/ccewh7OH.o: warning: relocation against `_ZN1C5XYZZYE' in
read-only section `.text._ZN1C1fEv[_ZN1C1fEv]'
/usr/bin/ld: /tmp/ccewh7OH.o: in function `C::f()':
foo.cpp:(.text._ZN1C1fEv[_ZN1C1fEv]+0xe): undefined reference to `C::XYZZY'
/usr/bin/ld: warning: creating DT_TEXTREL in a PIE
collect2: error: ld returned 1 exit status



gcc -v  

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 11.2.0-14'
--with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-y1lmfE/gcc-11-11.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-y1lmfE/gcc-11-11.2.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (Debian 11.2.0-14)