1.0: libwacom is not LTO ready

[kloczek]

When compiled with LTO optimisation linkiong of the test suite fails:

[tkloczko@barrel test]$ make
/bin/sh ../libtool  --tag=CC   --mode=link gcc  -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -flto -Os -no-install -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -flto -fuse-linker-plugin -o test-deprecated test-deprecated.o ../libwacom/libwacom.la  -ldl 
libtool: link: gcc -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -flto -Os -Wl,-z -Wl,relro -Wl,--as-needed -Wl,-z -Wl,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -flto -fuse-linker-plugin -o test-deprecated test-deprecated.o  ../libwacom/.libs/libwacom.so -lgudev-1.0 -lgobject-2.0 -lglib-2.0 -ldl -Wl,-rpath -Wl,/home/tkloczko/rpmbuild/BUILD/libwacom-0.99.901/libwacom/.libs
/usr/bin/ld: /tmp/test-deprecated.thrYTc.ltrans0.ltrans.o: in function `main':
/home/tkloczko/rpmbuild/BUILD/libwacom-0.99.901/test/test-deprecated.c:77: undefined reference to `libwacom_match_destroy@LIBWACOM_0.33'
/usr/bin/ld: /home/tkloczko/rpmbuild/BUILD/libwacom-0.99.901/test/test-deprecated.c:78: undefined reference to `libwacom_match_new@LIBWACOM_0.33'
/usr/bin/ld: /home/tkloczko/rpmbuild/BUILD/libwacom-0.99.901/test/test-deprecated.c:79: undefined reference to `libwacom_error_set@LIBWACOM_0.33'
/usr/bin/ld: /home/tkloczko/rpmbuild/BUILD/libwacom-0.99.901/test/test-deprecated.c:80: undefined reference to `libwacom_stylus_destroy@LIBWACOM_0.33'
/usr/bin/ld: /home/tkloczko/rpmbuild/BUILD/libwacom-0.99.901/test/test-deprecated.c:81: undefined reference to `libwacom_update_match@LIBWACOM_0.33'
collect2: error: ld returned 1 exit status
make: *** [Makefile:664: test-deprecated] Error 1
make: Target 'all' not remade because of errors.

[kloczek]

The same is when libwacom is build using meson.

[whot]

Any suggestions on how to fix this? this test is largely to verify that the symbols are still in the library (through dlsym and asm mappings) so I think this is fine to fail under LTO and just needs to be disabled when LTO is active. Not 100% sure though where LTO kicks in here.

[kloczek]

Please have look on other simillar case
SELinuxProject/selinux#169

[whot]

thanks, but I admit it doesn't give me enough details to continue. I managed to reproduce with export CC="gcc -flto" before meson, so it's confirmed at least. But looking at the libwacom.so now shows:

000000000000971e t libwacom_error_set@LIBWACOM_0.33
00000000000096fc t libwacom_match_destroy@LIBWACOM_0.33
0000000000009706 t libwacom_match_new@LIBWACOM_0.33
0000000000009775 t libwacom_stylus_destroy@LIBWACOM_0.33
000000000000977f t libwacom_update_match@LIBWACOM_0.33

So these functions are now local. This indicates that the LTO modifies the the .so file, it's not just an issue in the test. This would be an ABI break which is something I tried to avoid with the whole symbol dance here.

So - what's going on and how do I fix this?