[PATCH] ld: entry size and merge/strings attributes propagation

[Jan Beulich]

PR ld/33291

As indicated in other recent commits, the three properties can be
largely independent (ELF generally being the target here): Entry size
doesn't require either of merge/strings, and strings also doesn't
require merge. Commit 98e6d3f5bd4e ("gas/ELF: allow specifying entity
size for arbitrary sections") uncovered issues with ld's handling.

Zap entry size when it doesn't match between input sections. In that
case SEC_MERGE and SEC_STRINGS also need to be removed, as their
underlying granularity is lost. Then deal with SEC_MERGE and
SEC_STRINGS separately.

Otoh record entry size from the first input independent of SEC_MERGE.
---
The handling of the three attributes still isn't correct when it comes
to data allocation statements within the section, or position changes
(including alignment other than at the start): These would all need to
clear entry size (for not coming with an entry size themselves), and
hence also SEC_MERGE and SEC_STRINGS.

--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -2857,14 +2857,24 @@ lang_add_section (lang_statement_list_ty
       /* Only set SEC_READONLY flag on the first input section.  */
       flags &= ~ SEC_READONLY;
 
-      /* Keep SEC_MERGE and SEC_STRINGS only if they are the same.  */
-      if ((output->bfd_section->flags & (SEC_MERGE | SEC_STRINGS))
-	  != (flags & (SEC_MERGE | SEC_STRINGS))
-	  || ((flags & SEC_MERGE) != 0
-	      && output->bfd_section->entsize != section->entsize))
+      /* Keep entry size, SEC_MERGE, and SEC_STRINGS only if entry sizes are
+	 the same.  */
+      if (output->bfd_section->entsize != section->entsize)
 	{
-	  output->bfd_section->flags &= ~ (SEC_MERGE | SEC_STRINGS);
-	  flags &= ~ (SEC_MERGE | SEC_STRINGS);
+	  output->bfd_section->entsize = 0;
+	  flags &= ~(SEC_MERGE | SEC_STRINGS);
+	}
+
+      /* Keep SEC_MERGE and SEC_STRINGS (each) only if they are the same.  */
+      if ((output->bfd_section->flags ^ flags) & SEC_MERGE)
+	{
+	  output->bfd_section->flags &= ~SEC_MERGE;
+	  flags &= ~SEC_MERGE;
+	}
+      if ((output->bfd_section->flags ^ flags) & SEC_STRINGS)
+	{
+	  output->bfd_section->flags &= ~SEC_STRINGS;
+	  flags &= ~SEC_STRINGS;
 	}
     }
   output->bfd_section->flags |= flags;
@@ -2879,8 +2889,7 @@ lang_add_section (lang_statement_list_ty
 				     link_info.output_bfd,
 				     output->bfd_section,
 				     &link_info);
-      if ((flags & SEC_MERGE) != 0)
-	output->bfd_section->entsize = section->entsize;
+      output->bfd_section->entsize = section->entsize;
     }
 
   if ((flags & SEC_TIC54X_BLOCK) != 0