Re: [PATCH] compress .gnu.debuglto_.debug_* sections if requested

[Alan Modra <amodra@gmail.com>]

On Fri, Sep 30, 2022 at 09:19:49AM +0200, Martin Liška wrote:
> 	* write.c (compress_debug): Compress also ".gnu.debuglto_.debug_"
> 	if the compression algorithm is different from zlib-gnu.

OK, choosing to skip compression for zlib-gnu is a reasonable approach
given that zlib-gnu has the clunky .debug_* to .zdebug_* section
renaming scheme.  I'm going to commit your patch, but then enable
zlib-gnu with a followup patch of mine that doesn't rename the lto
debug sections.  ld.bfd and the binutils work fine without renaming,
but there may be some other reason why zlib-gnu must have .zdebug
sections.  If that turns out to be the case, my patch below can be
reverted.

bfd/
	* elf.c (elf_fake_sections): Replace "." with ".z" in debug
	section names only when name was ".d*", ie. ".debug_*".
	(_bfd_elf_assign_file_positions_for_non_load): Likewise.
gas/
	* write.c (compress_debug): Compress .gnu.debuglto_.debug_*
	for zlib-gnu too.  Compress .gnu.linkonce.wi.*.

diff --git a/bfd/elf.c b/bfd/elf.c
index 8cd257fc65c..420b524aae8 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -3234,7 +3234,8 @@ elf_fake_sections (bfd *abfd, asection *asect, void *fsarg)
 	      name = new_name;
 	    }
 	}
-      else if (asect->compress_status == COMPRESS_SECTION_DONE)
+      else if (asect->compress_status == COMPRESS_SECTION_DONE
+	       && name[1] == 'd')
 	{
 	  /* PR binutils/18087: Compression does not always make a
 	     section smaller.  So only rename the section when
@@ -3246,7 +3247,6 @@ elf_fake_sections (bfd *abfd, asection *asect, void *fsarg)
 	      arg->failed = true;
 	      return;
 	    }
-	  BFD_ASSERT (name[1] != 'z');
 	  name = new_name;
 	}
     }
@@ -6689,7 +6689,8 @@ _bfd_elf_assign_file_positions_for_non_load (bfd *abfd)
 		    return false;
 
 		  if (sec->compress_status == COMPRESS_SECTION_DONE
-		      && (abfd->flags & BFD_COMPRESS_GABI) == 0)
+		      && (abfd->flags & BFD_COMPRESS_GABI) == 0
+		      && name[1] == 'd')
 		    {
 		      /* If section is compressed with zlib-gnu, convert
 			 section name from .debug_* to .zdebug_*.  */
diff --git a/gas/write.c b/gas/write.c
index b8d5253006c..30f6c110908 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -1473,7 +1473,7 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
   char *header;
   int x;
   flagword flags = bfd_section_flags (sec);
-  unsigned int header_size, compression_header_size;
+  unsigned int header_size;
 
   if (seginfo == NULL
       || sec->size < 32
@@ -1482,8 +1482,8 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
 
   section_name = bfd_section_name (sec);
   if (!startswith (section_name, ".debug_")
-      && (!startswith (section_name, ".gnu.debuglto_.debug_")
-	  || flag_compress_debug == COMPRESS_DEBUG_GNU_ZLIB))
+      && !startswith (section_name, ".gnu.debuglto_.debug_")
+      && !startswith (section_name, ".gnu.linkonce.wi."))
     return;
 
   bool use_zstd = abfd->flags & BFD_COMPRESS_ZSTD;
@@ -1492,16 +1492,9 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
     return;
 
   if (flag_compress_debug == COMPRESS_DEBUG_GNU_ZLIB)
-    {
-      compression_header_size = 0;
-      header_size = 12;
-    }
+    header_size = 12;
   else
-    {
-      compression_header_size
-	= bfd_get_compression_header_size (stdoutput, NULL);
-      header_size = compression_header_size;
-    }
+    header_size = bfd_get_compression_header_size (stdoutput, NULL);
 
   /* Create a new frag to contain the compression header.  */
   first_newf = frag_alloc (ob);
@@ -1609,7 +1602,8 @@ compress_debug (bfd *abfd, asection *sec, void *xxx ATTRIBUTE_UNUSED)
   bfd_update_compression_header (abfd, (bfd_byte *) header, sec);
   x = bfd_set_section_size (sec, compressed_size);
   gas_assert (x);
-  if (!compression_header_size)
+  if (flag_compress_debug == COMPRESS_DEBUG_GNU_ZLIB
+      && section_name[1] == 'd')
     {
       compressed_name = concat (".z", section_name + 1, (char *) NULL);
       bfd_rename_section (sec, compressed_name);


-- 
Alan Modra
Australia Development Lab, IBM