powerpc64: Use medium model toc accesses throughout

The PowerPC64 linker edits medium model toc-indirect code to toc-pointer
relative:
	addis r9,r2,tc_entry_for_var@toc@ha
	ld r9,tc_entry_for_var@toc@l(r9)
becomes
	addis r9,r2,(var-.TOC.)@ha
	addi r9,r9,(var-.TOC.)@l
when "var" is known to be local to the binary.  This isn't done for
small-model toc-indirect code, because "var" is almost guaranteed to
be too far away from .TOC. for a 16-bit signed offset.  And, because
the analysis of which .toc entry can be removed becomes much more
complicated in objects that mix code models, they aren't removed if
any small-model toc sequence appears in an object file.

Unfortunately, glibc's build of ld.so smashes the needed objects
together in a ld -r linking stage.  This means the GOT/TOC is left
with a whole lot of relative relocations which is untidy, but in
itself is not a serious problem.  However, static-pie on powerpc64
bombs due to a segfault caused by one of the small-model accesses
before _dl_relocate_static_pie.  (The very first one in rcrt1.o
passing start_addresses in r8 to __libc_start_main.)

So this patch makes all the toc/got accesses in assembly medium code
model, and a couple of functions hidden.  By itself this is not
enough to give us working static-pie, but it is useful in isolation to
enable better linker optimisation.

There's a serious problem in libgcc too.  libgcc ifuncs access the
AT_HWCAP words stored in the tcb with an offset from the thread
pointer (r13), but r13 isn't set at the time _dl_relocate_static_pie.
A followup patch will fix that.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/sysdeps/powerpc/powerpc64/start.S b/sysdeps/powerpc/powerpc64/start.S
index 4319dc8d3e..244d9da07b 100644
--- a/sysdeps/powerpc/powerpc64/start.S
+++ b/sysdeps/powerpc/powerpc64/start.S
@@ -74,7 +74,8 @@ ENTRY (_start)
 
  /* put the address of start_addresses in r8...  **
 ** PPC64 ABI uses R13 for thread local, so we leave it alone */
-	ld	r8,.L01@toc(r2)
+	addis	r8,r2,.L01@toc@ha
+	ld	r8,.L01@toc@l(r8)
 
  /* and continue in libc-start, in glibc.  */
 	b	JUMPTARGET(__libc_start_main)