On Sat, May 16, 2015 at 7:19 AM, H.J. Lu <hjl.to...@gmail.com> wrote: > 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
It doesn't work. REG must hold GOT base for other GOT relocations. We need to keep addl $_GLOBAL_OFFSET_TABLE_, %eax -- H.J.
