On Fri, Dec 23, 2016 at 12:11 PM, Joerg Sonnenberger <jo...@bec.de> wrote: > On Fri, Dec 23, 2016 at 11:27:15AM -0800, Philip Guenther wrote: >> This is a form we use inside _libc_ so that calls to those functions >> generated by gcc will be redirected to aliases with hidden visibility >> and thus be local calls, without using the PLT. If that won't work >> with clang, then we'll want to figure out some other way to get the >> calls to those functions generated by the compiler to be local calls >> inside libc. > > I'm not sure about all possible platforms, but for all I can think of, > it is enough if the target is hidden.
Making memcpy hidden is fine for ld.so, but not for libc, thus the alias and asm rename dance we're currently using. > In that case ld should be using > a direct jump/call to the destination without creating a PLT entry. The linker can eliminate the PLT entry and double-jump, but it currently can't reoptimize the calling functions when %ebx is no longer needed for holding the GOT offset for the PLT call. LTO is getting better, I guess, but it was nice getting the Right Thing without requiring it. <shrug> Philip Guenther
