[binutils-gdb] PowerPC64 .branch_lt size change leads to "stubs don't match calculated size"

[Alan Modra <amodra at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ba21f5646454c418e75eb06f6bf1a00a173641ca

commit ba21f5646454c418e75eb06f6bf1a00a173641ca
Author: Alan Modra <amodra@gmail.com>
Date:   Fri Jan 26 12:25:09 2018 +1030

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

Diff:
---
 bfd/ChangeLog   | 5 +++++
 bfd/elf64-ppc.c | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index ba377ab..4ad0127 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -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
diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index b2d288b..5cbb035 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -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;