On Fri, May 15, 2015 at 4:49 PM, Rich Felker <dal...@libc.org> wrote: > On Fri, May 15, 2015 at 04:34:57PM -0700, H.J. Lu wrote: >> On Fri, May 15, 2015 at 4:30 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >> > On Fri, May 15, 2015 at 4:14 PM, H.J. Lu <hjl.to...@gmail.com> wrote: >> >> My relax branch proposal works even without LTO. >> >> >> > >> > I will borrow GOTPCREL from x86-64 and do >> > >> > [hjl@gnu-6 relax-4]$ cat b.S >> > call *foo@GOTPCREL(%eax) >> >> call *foo@GOTPLT(%eax) >> >> is a better choice. > > foo@GOTPCREL is preferable (but does not yet exist for ia32, so the > reloc type would have to be added) since it saves a useless add. > Instead of: > > call __x86.get_pc_thunk.ax > addl $_GLOBAL_OFFSET_TABLE_, %eax > call *foo@GOTPLT(%eax) > > you can just do: > > call __x86.get_pc_thunk.ax > call *foo@GOTPCREL(%eax) > > Note that it also works to have extra instructions between: > > call __x86.get_pc_thunk.ax > 1: ... > call *foo@GOTPCREL+(1b-.)(%eax) > > I may not have gotten the syntax quite right, but hopefully yoy get > the idea. This same approach (with GOTPCREL) can be used for _all_ GOT > accesses, including global data, to eliminate the useless add. >
This is a good idea. But I'd like to use something for both i386 and x86-64. I am proposing call/jmp *foo@GOTPCRELAX+addend(%reg) It is similar to @GOTPCREL, but with a new relax relocation. Before I can do that, I need to fix https://sourceware.org/bugzilla/show_bug.cgi?id=18423 first. -- H.J.
