Hi there - I'm not a CMake person, but a Clang/LLVM developer who helped in the implementation of Split DWARF in Clang/LLVM, so I know a bit about DWOs and DWPs, etc & thought I'd offer a few extra details...
On Fri, Dec 21, 2018 at 3:39 AM David Jobet <djo...@tower-research.com> wrote: > Hello, > > in order to speed up our link step, I wanted to experiment with split > dwarf. > See http://www.productive-cpp.com/improving-cpp-builds-with-split-dwarf/ > > Adding the compilation flag is easy, but I'm stumbling on the installation > step. > In our current mode, we redirect the STRIP step to extract the symbols > and strip the binary. > When you say "symbols" - do you mean only debug info? Or other things (like the ELF symbol table (.symtab section) - since they're no longer needed if no one's calling into the binary (I guess maybe a symbol table that contains the entry point - 'main' would be needed? - this is the part of ELF I don't understand too well)) > With split dwarf, I want to use 'dwp' to collect all .dwo files and > assemble a symbol file. No need to strip I guess since symbols are > already put elsewhere. > Actually there's probably still a desire to strip the executable - Split DWARF leaves some debug info in the .o/executable (& at least the GNU extension form of Split DWARF available in DWARFv4 leaves quiet a bit in the .o/executable, especially in an optimized build, unfortunately) that you can benefit from stripping out - along with the non-debug-related symbol table, if that's a thing you're stripping (see above). > So I figure I would just use dwp as the strip command in my custom > strip command. > > Problem is .dwo files are recorded in the .o files relative to the > build directory and the strip command is executed on the installed > directory. > I think this depends on your build system - and might be resolvable relative to the comp_dir in the debug info remaining in the .o file? Though I haven't looked/checked closely (but yeah, moving debug info around when using Split DWARF is a bit tricky) > As a result, 'dwp' complains it cannot find the .dwo files. > > I don't want to add a POST_BUILD step on each our binaries (we have > lots of binaries), and anyway I'd rather prefer to have the 'dwp' step > executed at install time so it's executed only when we want to > deliver. > > Is there a way to either > - pass the build_dir to the strip command ? > - define a custom step of the install process that would execute on > the build dir previous to the install step itself ? (for the same > reason I don't want to manually define a POST_BUILD step on each > binaries, I don't want to manually define a custom INSTALL step that > would precede the INSTALL step of all our binaries) > - or another option ? > > With regards > > David > -- > > Powered by www.kitware.com > > Please keep messages on-topic and check the CMake FAQ at: > http://www.cmake.org/Wiki/CMake_FAQ > > Kitware offers various services to support the CMake community. For more > information on each offering, please visit: > > CMake Support: http://cmake.org/cmake/help/support.html > CMake Consulting: http://cmake.org/cmake/help/consulting.html > CMake Training Courses: http://cmake.org/cmake/help/training.html > > Visit other Kitware open-source projects at > http://www.kitware.com/opensource/opensource.html > > Follow this link to subscribe/unsubscribe: > https://cmake.org/mailman/listinfo/cmake >
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