Compiling LO for lcov/gcov code coverage fails (gb_GCOV=YES)

[Stephan Bergmann]

On 5/12/22 15:44, Maarten Hoes wrote:
> What I *think* I see happening, is that the '-fprofile-arcs 
> -ftest-coverage -lgcov' flags are correctly being set on the 
> commandlines, up until were the error occurs, which is where (i think) 
> linking against libpng is attempted (see error below). I tried setting 
> *FLAGS in 'external/libpng/StaticLibrary_libpng.mk', but that did not 
> change things. Am I misunderstanding what is happening here, or perhaps 
> modifying the wrong Makefile ? I cannot really tell what is going on 
> here, or what to try next.

I guess it just doesn't work well to link an archive like 
workdir/LinkTarget/StaticLibrary/liblibpng.a built with GCC and 
-fprofile-arcs into a library like Library_skia built with Clang and 
-fprofile-arcs:  GCC -fprofile-arcs embeds calls to __gcov_init etc. 
into the code (satisfied at link time from GCC's libgcov.a) while Clang 
-fprofile-arcs embeds calls to llvm_gcov_init etc. into the code 
(satisfied at link time from Clang's libclang_rt.profile-*.a).  The way 
that normally works is that when you use g++ -fprofile-arcs for linking, 
it sneaks in a -lgcov towards the end of the command line that it passes 
to the linker, and when you use clang++ -fprofile-arcs for linking, it 
sneaks in a /path-to/libclang_rt.profile-*.a towards the end of the 
command line that it passes to the linker.  You have (multiple, even) 
explicit -lgocv on your clang++ -fprofile-arcs command line for linking 
Library_skia, but that comes too early before the -Wl,--start-group ... 
$W/LinkTarget/StaticLibrary/liblibpng.a ... -Wl,--end-group, so can't be 
used to satisfy that archive's dependency on __gcov_init etc.  (And the 
later, sneaked in, /path-to/libclang_rt.profile-*.a doesn't satisfy 
those dependencies either, as it rather supplies llvm_gcov_init etc.)

Maybe it would be best if the decision to force using Clang for building 
Library_skia would be explicitly opt-in or opt-out.