Fix debug section compression so that it is only performed if it would make the section smaller.

	PR binutils/18087
gas	* doc/as.texinfo: Note that when gas compresses debug sections the
	compression is only performed if it makes the section smaller.
	* write.c (compress_debug): Do not compress a debug section if
	doing so would make it larger.

tests	* gas/i386/dw2-compress-1.d: Do not expect the .debug_abbrev or
	.debug_info sections to be compressed.

binu	* doc/binutils.texi: Note that when objcopy compresses debug
	sections the compression is only performed if it makes the section
	smaller.

bfd	* coffgen.c (make_a_section_from_file): Only prepend a z to a
	debug section's name if the section was actually compressed.
	* elf.c (_bfd_elf_make_section_from_shdr): Likewise.
	* compress.c (bfd_init_section_compress_status): Do not compress
	the section if doing so would make it bigger.  In such cases leave
	the section alone and return COMPRESS_SECTION_NONE.

5 files changed, 25 insertions, 3 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index bccf7b30..7bf7794 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,12 @@
+2015-03-18  Jon Turney  <jon.turney@dronecode.org.uk>
+	    Nick Clifton  <nickc@redhat.com>
+
+	PR binutils/18087
+	* doc/as.texinfo: Note that when gas compresses debug sections the
+	compression is only performed if it makes the section smaller.
+	* write.c (compress_debug): Do not compress a debug section if
+	doing so would make it larger.
+
 2015-03-17  Ganesh Gopalasubramanian  <Ganesh.Gopalasubramanian@amd.com>
 
 	* config/tc-i386.c (cpu_arch): Add PROCESSOR_ZNVER flags.
diff --git a/gas/doc/as.texinfo b/gas/doc/as.texinfo
index 36c2207..bedb4d5 100644
--- a/gas/doc/as.texinfo
+++ b/gas/doc/as.texinfo
@@ -627,7 +627,8 @@ Begin in alternate macro mode.
 @item --compress-debug-sections
 Compress DWARF debug sections using zlib.  The debug sections are renamed
 to begin with @samp{.zdebug}, and the resulting object file may not be
-compatible with older linkers and object file utilities.
+compatible with older linkers and object file utilities.  Note if compression
+would make a given section @emph{larger} then it is not compressed or renamed.
 
 @item --nocompress-debug-sections
 Do not compress DWARF debug sections.  This is the default.
diff --git a/gas/testsuite/ChangeLog b/gas/testsuite/ChangeLog
index 3b58c97..5b16085 100644
--- a/gas/testsuite/ChangeLog
+++ b/gas/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2015-03-18  Jon Turney  <jon.turney@dronecode.org.uk>
+	    Nick Clifton  <nickc@redhat.com>
+
+	PR binutils/18087
+	* gas/i386/dw2-compress-1.d: Do not expect the .debug_abbrev or
+	.debug_info sections to be compressed.
+
 2015-03-17  Ganesh Gopalasubramanian  <Ganesh.Gopalasubramanian@amd.com>
 
 	* gas/i386/i386.exp: Add new znver1 test cases.
diff --git a/gas/testsuite/gas/i386/dw2-compress-1.d b/gas/testsuite/gas/i386/dw2-compress-1.d
index 4d1a393..2b2fd8d 100644
--- a/gas/testsuite/gas/i386/dw2-compress-1.d
+++ b/gas/testsuite/gas/i386/dw2-compress-1.d
@@ -2,7 +2,7 @@
 #readelf: -w
 #name: DWARF2 debugging information 1
 
-Contents of the .zdebug_info section:
+Contents of the .debug_info section:
 
   Compilation Unit @ offset 0x0:
    Length:        0x4e \(32-bit\)
@@ -31,7 +31,7 @@ Contents of the .zdebug_info section:
     <50>   DW_AT_encoding    : 5	\(signed\)
  <1><51>: Abbrev Number: 0
 
-Contents of the .zdebug_abbrev section:
+Contents of the .debug_abbrev section:
 
   Number TAG \(0x0\)
    1      DW_TAG_compile_unit    \[has children\]
diff --git a/gas/write.c b/gas/write.c
index 949ae92..e3570ac 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -1526,6 +1526,11 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
 	break;
     }
 
+  /* PR binutils/18087: If compression didn't make
+     the section smaller, just keep it uncompressed.  */
+  if (compressed_size > sec->size)
+    return;
+  
   /* Replace the uncompressed frag list with the compressed frag list.  */
   seginfo->frchainP->frch_root = first_newf;
   seginfo->frchainP->frch_last = last_newf;