binutils/ld: fix incorrect placement of __start_SECNAME in some cases

__start_SECNAME and __stop_SECNAME symbols are automatically generated
by ld for orphan sections, i.e. those not explicitely referenced by a
linker script.  The symbols are supposed to be placed correspondingly
at the start and the end of the section in output file.  In some cases
__start_SECNAME may be placed at the address after the end of the
previous section (if any) and before the start the section.  This
happens when following conditions are met:
1. the orphan section is found in more than one input file
2. the orphan section has different alignment requirements across input
files
3. the first instance of the section encountered doesn't have the
greatest alignment requirement
In these conditions resulting output section will be placed at address
after the end of the previous section aligned to the greatest alignment
requirement in the inputs, but __start_SECNAME will be placed at address
after the end of the previous section aligned to the alignment
requirement of the first input in which the section is encountered.

See commit message of r196118 for a concrete example of problems caused
by this bug.

The fix is to place __start_SECNAME inside the section and use ABSOLUTE
directive, rather than placing __start_SECNAME outside the section and
trying to guess address alignment.

This fix is in line with upstream binutils change/fix made between
versions 2.19 and 2.20 in revision of 1.307 ldlang.c.

MFC after:	3 weeks

1 files changed, 20 insertions, 20 deletions

diff --git a/contrib/binutils/ld/emultempl/elf32.em b/contrib/binutils/ld/emultempl/elf32.em
index 4a31b48..b970e56 100644
--- a/contrib/binutils/ld/emultempl/elf32.em
+++ b/contrib/binutils/ld/emultempl/elf32.em
@@ -1314,26 +1314,6 @@ gld${EMULATION_NAME}_place_orphan (lang_input_statement_type *file, asection *s)
       lang_list_init (stat_ptr);
     }
 
-  if (config.build_constructors)
-    {
-      /* If the name of the section is representable in C, then create
-	 symbols to mark the start and the end of the section.  */
-      for (ps = secname; *ps != '\0'; ps++)
-	if (! ISALNUM (*ps) && *ps != '_')
-	  break;
-      if (*ps == '\0')
-	{
-	  char *symname;
-	  etree_type *e_align;
-
-	  symname = (char *) xmalloc (ps - secname + sizeof "__start_");
-	  sprintf (symname, "__start_%s", secname);
-	  e_align = exp_unop (ALIGN_K,
-			      exp_intop ((bfd_vma) 1 << s->alignment_power));
-	  lang_add_assignment (exp_assop ('=', symname, e_align));
-	}
-    }
-
   address = NULL;
   if (link_info.relocatable || (s->flags & (SEC_LOAD | SEC_ALLOC)) == 0)
     address = exp_intop ((bfd_vma) 0);
@@ -1354,6 +1334,26 @@ gld${EMULATION_NAME}_place_orphan (lang_input_statement_type *file, asection *s)
 					    (etree_type *) NULL,
 					    load_base);
 
+  if (config.build_constructors)
+    {
+      /* If the name of the section is representable in C, then create
+	 symbols to mark the start and the end of the section.  */
+      for (ps = secname; *ps != '\0'; ps++)
+	if (! ISALNUM (*ps) && *ps != '_')
+	  break;
+      if (*ps == '\0')
+	{
+	  char *symname;
+	  etree_type *e_align;
+
+	  symname = (char *) xmalloc (ps - secname + sizeof "__start_");
+	  sprintf (symname, "__start_%s", secname);
+	  lang_add_assignment (exp_assop ('=', symname,
+					  exp_unop (ABSOLUTE,
+						    exp_nameop (NAME, "."))));
+	}
+    }
+
   lang_add_section (&os->children, s, os, file);
 
   lang_leave_output_section_statement