[vta, trunk?] ignore .cfi_*-induced .eh_frame compare-debug differences

[Alexandre Oliva <aoliva at redhat dot com>]

bootstrap-debug is broken in trunk and vta branch on machines that
support assembler-generated CFI and that don't generate CFI by ABI
requirements.  I got bootstrap-debug failures on at least i686 and
ppc64, because compilations with -g0 didn't have an .eh_frame section,
whereas such trivial translation units as ada/final got a simple
.eh_frame section with -g2, because .cfi_startproc and .cfi_endproc
are enough to cause the generation of .eh_frame in addition to debug
info.

I suppose enabling the assembler to tell whether or not we're
interested in .eh_frame, in addition to .debug_frame, would be a win
in terms of stripped binary size, but I wasn't sure it was worth the
effort.  Thoughts?

In the meantime, I needed some way to ignore these differences, so I
came up with this patch, that will discard the .eh_frame section from
one of the object files if the other doesn't have one, and then retry
the object file compare.  This fixed all the boostrap-debug failures I
had.

I'm installing this in the branch.  Is this enough of a regression fix
to make it acceptable for the trunk?


for  contrib/ChangeLog.vta
from  Alexandre Oliva  <aoliva@redhat.com>

	* compare-debug: Don't fail just because of .eh_frame differences.

Index: contrib/compare-debug
===================================================================
--- contrib/compare-debug.orig	2008-11-15 21:13:26.000000000 -0200
+++ contrib/compare-debug	2008-11-15 21:14:11.000000000 -0200
@@ -2,7 +2,7 @@
 
 # Compare stripped copies of two given object files.
 
-# Copyright (C) 2007 Free Software Foundation
+# Copyright (C) 2007, 2008 Free Software Foundation
 # Originally by Alexandre Oliva <aoliva@redhat.com>
 
 # This file is part of GCC.
@@ -67,6 +67,82 @@ if cmp "$1.$suf1" "$2.$suf2"; then
   status=0
 else
   status=1
+
+  # Assembler-generated CFI will add an .eh_frame section for -g not
+  # present in -g0.  Try to cope with it by checking that an .eh_frame
+  # section is present in either object file, and then stripping it
+  # off before re-comparing.
+
+  cmd=
+  cmp1=
+  cmp2=
+
+  for t in objdump readelf eu-readelf; do
+    if ($t --help) 2>&1 | grep -e '--\[\?section-\]\?headers' > /dev/null; then
+      cmd=$t
+
+      $cmd --section-headers "$1.$suf1" | grep '\.eh_frame' > /dev/null
+      cmp1=$?
+
+      $cmd --section-headers "$2.$suf2" | grep '\.eh_frame' > /dev/null
+      cmp2=$?
+
+      break
+    fi
+  done
+
+  # If we found .eh_frame in one but not the other, or if we could not
+  # find a command to tell, try to strip off the .eh_frame section
+  # from both.
+  if test "x$cmp1" != "x$cmp2" || test "x$cmd" = "x"; then
+    suf3=$suf1.
+    while test -f "$1.$suf3"; do
+      suf3=$suf3.
+    done
+
+    suf4=$suf2.
+    while test -f "$2.$suf4"; do
+      suf4=$suf4.
+    done
+
+    trap 'rm -f "$1.$suf1" "$2.$suf2" "$1.$suf3" "$2.$suf4"' 0 1 2 15
+
+    if (objcopy -v) 2>&1 | grep -e "--remove-section" > /dev/null; then
+      objcopy --remove-section .eh_frame "$1.$suf1" "$1.$suf3"
+      cmp "$1.$suf1" "$1.$suf3" > /dev/null
+      cmp1=$?
+
+      objcopy --remove-section .eh_frame "$2.$suf2" "$2.$suf4"
+      cmp "$2.$suf2" "$2.$suf4" > /dev/null
+      cmp2=$?
+
+      mv "$1.$suf3" "$1.$suf1"
+      mv "$2.$suf4" "$2.$suf2"
+    elif (strip --help) 2>&1 | grep -e --remove-section > /dev/null; then
+      cp "$1.$suf1" "$1.$suf3"
+      strip --remove-section .eh_frame "$1.$suf3"
+
+      cp "$2.$suf2" "$2.$suf4"
+      strip --remove-section .eh_frame "$2.$suf4"
+
+      cmp "$1.$suf1" "$1.$suf3" > /dev/null
+      cmp1=$?
+
+      cmp "$2.$suf2" "$2.$suf4" > /dev/null
+      cmp2=$?
+
+      mv "$1.$suf3" "$1.$suf1"
+      mv "$2.$suf4" "$2.$suf2"
+    fi
+
+    trap 'rm -f "$1.$suf1" "$2.$suf2"' 0 1 2 15
+  fi
+
+  if test "x$cmp1" != "x$cmp2" && cmp "$1.$suf1" "$2.$suf2"; then
+    status=0
+  else
+    status=1
+  fi
 fi
 
 $rm "$1.$suf1" "$2.$suf2"

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}
FSFLA Board Member       ÂSÃ Libre! => http://www.fsfla.org/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}