On Tue, Mar 04, 2025 at 02:40:31PM +0100, Philippe Mathieu-Daudé wrote: > On 4/3/25 13:11, Daniel P. Berrangé wrote: > > On Tue, Mar 04, 2025 at 11:33:44AM +0000, Alex Bennée wrote: > > > Daniel P. Berrangé <berra...@redhat.com> writes: > > > > > > > On Mon, Mar 03, 2025 at 10:17:03PM +0000, Alex Bennée wrote: > > > > > This option is supported by both gcc (since 4.7) and clang (since > > > > > 7.0). Not only does this make the linkers job easier by reducing the > > > > > amount of ELF it needs to parse it also reduces the total build size > > > > > quite considerably. In my case a default build went from 5.8G to 3.9G. > > > > > > > > I've not come across this option before, but the docs say > > > > > > > > ‘-gsplit-dwarf’ > > > > If DWARF debugging information is enabled, separate as much > > > > debugging information as possible into a separate output file with > > > > the extension ‘.dwo’. This option allows the build system to > > > > avoid > > > > linking files with debug information. To be useful, this option > > > > requires a debugger capable of reading ‘.dwo’ files. > > > > > > > > In Fedora and RHEL we build QEMU will full debug enabled, and then a > > > > feature > > > > of the distro RPM build config will post-process all ELF files to > > > > extract > > > > the debug info into files that we store under /usr/lib/debug. eg for > > > > /usr/bin/qemu-system-x86_64, we get a separate > > > > /usr/lib/debug/bin/qemu-system-x86_64-9.1.3-1.fc41.x86_64.debug, and > > > > tools like GDB, etc know to look for these separate files. > > > > > > A modern gdb can certainly handle fetching the debug out of the .dwo > > > files when debugging. > > > > See this response from one of the upstream GCC maintainers pretty much > > recommending against (on by default) use of -gsplit-dwarf: > > > > > > https://lists.fedoraproject.org/archives/list/de...@lists.fedoraproject.org/thread/RXA55BTO62NWWHCTUFYGEVHJKZPL5EKE/ > > Jakub said: > > "it can be useful for fast modify/rebuild/test cycles during > development, but is something that is really undesirable for > the distro builds." > > Do distro use --enable-debug by default? Otherwise it might be > useful to add it for developers.
We don't have --enable-debug in Fedora/RHEL, and I doubt other distros would enable it given it turns off all optimization as well as introducing other static debug overheads. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
