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PowerPC64 .branch_lt size change leads to "stubs don't match calculated size"

Browse source 
https://bugzilla.redhat.com/show_bug.cgi?id=1523457

I haven't analyzed this myself, I'm relying on Nick's excellent
analysis.  What I believe is happening is that after some number of
stub sizing iterations, a long-branch stub needs to be converted to a
plt-branch, but either due to stub alignment or other stubs shrinking
in size, the stub group section size doesn't change.

That means we exit from ppc64_elf_size_stubs after sizing with an
incorrect layout, in fact the additional .branch_lt entry overlays
.got!  Since .TOC. is normally set to .got + 0x8000 the stub sizing
code decides that entry is within +/-32k of the TOC pointer and so a
three insn stub is sufficient.  When we come to build the stubs using
a correct non-overlaying layout, a four insn plt-branch stub is
generated and the stub group size doesn't match that calculated
earlier.

	* elf64-ppc.c (ppc64_elf_size_stubs): Iterate sizing when
	.branch_lt changes size.
This commit is contained in:
Alan Modra 2018-01-26 12:25:09 +10:30
parent 8a69c6d07b
commit ba21f56464
2 changed files with 11 additions and 0 deletions
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5
bfd/ChangeLog
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@ -1,3 +1,8 @@
2018-01-26 Alan Modra <amodra@gmail.com>
* elf64-ppc.c (ppc64_elf_size_stubs): Iterate sizing when
.branch_lt changes size.
2018-01-25 Alan Modra <amodra@gmail.com>
PR 22746

6
bfd/elf64-ppc.c
View file

@ -12702,6 +12702,9 @@ ppc64_elf_size_stubs (struct bfd_link_info *info)
stub_sec->flags &= ~SEC_RELOC;
}
if (htab->stub_iteration <= STUB_SHRINK_ITER
|| htab->brlt->rawsize < htab->brlt->size)
htab->brlt->rawsize = htab->brlt->size;
htab->brlt->size = 0;
htab->brlt->reloc_count = 0;
htab->brlt->flags &= ~SEC_RELOC;
@ -12757,6 +12760,9 @@ ppc64_elf_size_stubs (struct bfd_link_info *info)
break;
if (group == NULL
&& (htab->brlt->rawsize == htab->brlt->size
|| (htab->stub_iteration > STUB_SHRINK_ITER
&& htab->brlt->rawsize > htab->brlt->size))
&& (htab->glink_eh_frame == NULL
|| htab->glink_eh_frame->rawsize == htab->glink_eh_frame->size))
break;