Re: [libvirt] [PATCH 2/2] Revert "Prevent more compiler optimization of mockable functions"

On Wed, Jul 12, 2017 at 11:14:16AM +0100, Daniel P. Berrange wrote: >This reverts commit e4b980c853d2114b25fa805a84ea288384416221. > >When a binary links against a .a archive (as opposed to a shared library), >any symbols which are marked as 'weak' get silently dropped. As a result >when the binary later runs, those 'weak' functions have an address of >0x0 and thus crash when run. > >This happened with virtlogd and virtlockd because they don't link to >libvirt.so, but instead just libvirt_util.a and libvirt_rpc.a. The >virRandomBits symbols was weak and so left out of the virtlogd & >virtlockd binaries, despite being required by virHashTable functions. > >Various other binaries like libvirt_lxc, libvirt_iohelper, etc also >link directly to .a files instead of libvirt.so, so are potentially >at risk of dropping symbols leading to a later runtime crash. > >This is normal linker behaviour because a weak symbol is not treated >as undefined, so nothing forces it to be pulled in from the .a You >have to force the linker to pull in weak symbols using -u$SYMNAME >which is not a practical approach. > How is this done by gnulib (or libc) when most their functions are weak aliases anyway? Can't we use the same approach they have? virtlo{g,ck}d link with libgnu.la as well and there is no problem with that, right? So I guess this _must_ be solvable somehow, IMHO. I'm just curious how that works. Martin