ld: Allow section groups to be resolved as part of a relocatable link

This commit adds a new linker feature: the ability to resolve section
groups as part of a relocatable link.

Currently section groups are automatically resolved when performing a
final link, and are carried through when performing a relocatable link.
By carried through this means that one copy of each section group (from
all the copies that might be found in all the input files) is placed
into the output file.  Sections that are part of a section group will
not match input section specifiers within a linker script and are
forcibly kept as separate sections.

There is a slight resemblance between section groups and common
section.  Like section groups, common sections are carried through when
performing a relocatable link, and resolved (allocated actual space)
only at final link time.

However, with common sections there is an ability to force the linker to
allocate space for the common sections when performing a relocatable
link, there's currently no such ability for section groups.

This commit adds such a mechanism.  This new facility can be accessed in
two ways, first there's a command line switch --force-group-allocation,
second, there's a new linker script command FORCE_GROUP_ALLOCATION.  If
one of these is used when performing a relocatable link then the linker
will resolve the section groups as though it were performing a final
link, the section group will be deleted, and the members of the group
will be placed like normal input sections.  If there are multiple copies
of the group (from multiple input files) then only one copy of the group
members will be placed, the duplicate copies will be discarded.

Unlike common sections that have the --no-define-common command line
flag, and INHIBIT_COMMON_ALLOCATION linker script command there is no
way to prevent group resolution during a final link, this is because the
ELF gABI specifically prohibits the presence of SHT_GROUP sections in a
fully linked executable.  However, the code as written should make
adding such a feature trivial, setting the new resolve_section_groups
flag to false during a final link should work as you'd expect.

bfd/ChangeLog:

	* elf.c (_bfd_elf_make_section_from_shdr): Don't initially mark
	SEC_GROUP sections as SEC_EXCLUDE.
	(bfd_elf_set_group_contents): Replace use of abort with an assert.
	(assign_section_numbers): Use resolve_section_groups flag instead
	of relocatable link type.
	(_bfd_elf_init_private_section_data): Use resolve_section_groups
	flag instead of checking the final_link flag for part of the
	checks in here.  Fix white space as a result.
	* elflink.c (elf_link_input_bfd): Use resolve_section_groups flag
	instead of relocatable link type.
	(bfd_elf_final_link): Likewise.

include/ChangeLog:

	* bfdlink.h (struct bfd_link_info): Add new resolve_section_groups
	flag.

ld/ChangeLog:

	* ld.h (struct args_type): Add force_group_allocation field.
	* ldgram.y: Add support for FORCE_GROUP_ALLOCATION.
	* ldlex.h: Likewise.
	* ldlex.l: Likewise.
	* lexsup.c: Likewise.
	* ldlang.c (unique_section_p): Check resolve_section_groups flag
	not the relaxable link flag.
	(lang_add_section): Discard section groups when we're resolving
	groups.  Clear the SEC_LINK_ONCE flag if we're resolving section
	groups.
	* ldmain.c (main): Initialise resolve_section_groups flag in
	link_info based on command line flags.
	* testsuite/ld-elf/group11.d: New file.
	* testsuite/ld-elf/group12.d: New file.
	* testsuite/ld-elf/group12.ld: New file.
	* NEWS: Mention new features.
	* ld.texinfo (Options): Document --force-group-allocation.
	(Miscellaneous Commands): Document FORCE_GROUP_ALLOCATION.

13 files changed, 112 insertions, 4 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 0e52c27..e80477f 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,24 @@
+2017-06-06  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* ld.h (struct args_type): Add force_group_allocation field.
+	* ldgram.y: Add support for FORCE_GROUP_ALLOCATION.
+	* ldlex.h: Likewise.
+	* ldlex.l: Likewise.
+	* lexsup.c: Likewise.
+	* ldlang.c (unique_section_p): Check resolve_section_groups flag
+	not the relaxable link flag.
+	(lang_add_section): Discard section groups when we're resolving
+	groups.  Clear the SEC_LINK_ONCE flag if we're resolving section
+	groups.
+	* ldmain.c (main): Initialise resolve_section_groups flag in
+	link_info based on command line flags.
+	* testsuite/ld-elf/group11.d: New file.
+	* testsuite/ld-elf/group12.d: New file.
+	* testsuite/ld-elf/group12.ld: New file.
+	* NEWS: Mention new features.
+	* ld.texinfo (Options): Document --force-group-allocation.
+	(Miscellaneous Commands): Document FORCE_GROUP_ALLOCATION.
+
 2017-06-05  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR ld/21529
diff --git a/ld/NEWS b/ld/NEWS
index 52daa6b..98055b5 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -15,6 +15,11 @@
 * Orphan sections placed after an empty section that has an AT(LMA) will now
   take an load memory address starting from LMA.
 
+* Section groups can now be resolved (the group deleted and the group members
+  placed like normal sections) at partial link time either using the new linker
+  option --force-group-allocation or by placing FORCE_GROUP_ALLOCATION into the
+  linker script.
+
 Changes in 2.28:
 
 * The EXCLUDE_FILE linker script construct can now be applied outside of the
diff --git a/ld/ld.h b/ld/ld.h
index 104bb8e..d9bb653 100644
--- a/ld/ld.h
+++ b/ld/ld.h
@@ -172,6 +172,11 @@ typedef struct
   /* If set, display the target memory usage (per memory region).  */
   bfd_boolean print_memory_usage;
 
+  /* Shold we force section groups to be resolved?  Controlled with
+     --force-group-allocation on the command line or FORCE_GROUP_ALLOCATION
+     in the linker script.  */
+  bfd_boolean force_group_allocation;
+
   /* Big or little endian as set on command line.  */
   enum endian_enum endian;
 
diff --git a/ld/ld.texinfo b/ld/ld.texinfo
index edf1e31..790b52f 100644
--- a/ld/ld.texinfo
+++ b/ld/ld.texinfo
@@ -1484,6 +1484,18 @@ and also prevents any possible confusion over resolving to the wrong
 duplicate when there are many dynamic modules with specialized search
 paths for runtime symbol resolution.
 
+@cindex group allocation in linker script
+@cindex section groups
+@cindex COMDAT
+@kindex --force-group-allocation
+@item --force-group-allocation
+This option causes the linker to place section group members like
+normal input sections, and to delete the section groups.  This is the
+default behaviour for a final link but this option can be used to
+change the behaviour of a relocatable link (@samp{-r}).  The script
+command @code{FORCE_GROUP_ALLOCATION} has the same
+effect. @xref{Miscellaneous Commands}.
+
 @cindex symbols, from command line
 @kindex --defsym=@var{symbol}=@var{exp}
 @item --defsym=@var{symbol}=@var{expression}
@@ -3726,6 +3738,17 @@ This command has the same effect as the @samp{--no-define-common}
 command-line option: to make @code{ld} omit the assignment of addresses
 to common symbols even for a non-relocatable output file.
 
+@item FORCE_GROUP_ALLOCATION
+@kindex FORCE_GROUP_ALLOCATION
+@cindex group allocation in linker script
+@cindex section groups
+@cindex COMDAT
+This command has the same effect as the
+@samp{--force-group-allocation} command-line option: to make
+@command{ld} place section group members like normal input sections,
+and to delete the section groups even if a relocatable output file is
+specified (@samp{-r}).
+
 @item INSERT [ AFTER | BEFORE ] @var{output_section}
 @kindex INSERT
 @cindex insert user script into default script
diff --git a/ld/ldgram.y b/ld/ldgram.y
index 849f272..4c1efdc 100644
--- a/ld/ldgram.y
+++ b/ld/ldgram.y
@@ -131,7 +131,7 @@ static int error_index;
 %token SORT_BY_INIT_PRIORITY
 %token '{' '}'
 %token SIZEOF_HEADERS OUTPUT_FORMAT FORCE_COMMON_ALLOCATION OUTPUT_ARCH
-%token INHIBIT_COMMON_ALLOCATION
+%token INHIBIT_COMMON_ALLOCATION FORCE_GROUP_ALLOCATION
 %token SEGMENT_START
 %token INCLUDE
 %token MEMORY
@@ -336,6 +336,8 @@ ifile_p1:
 		  { ldfile_set_output_arch ($3, bfd_arch_unknown); }
 	|	FORCE_COMMON_ALLOCATION
 		{ command_line.force_common_definition = TRUE ; }
+	|	FORCE_GROUP_ALLOCATION
+		{ command_line.force_group_allocation = TRUE ; }
 	|	INHIBIT_COMMON_ALLOCATION
 		{ command_line.inhibit_common_definition = TRUE ; }
 	|	INPUT '(' input_list ')'
diff --git a/ld/ldlang.c b/ld/ldlang.c
index ed7e552..252400b 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -207,7 +207,7 @@ unique_section_p (const asection *sec,
   struct unique_sections *unam;
   const char *secnam;
 
-  if (bfd_link_relocatable (&link_info)
+  if (!link_info.resolve_section_groups
       && sec->owner != NULL
       && bfd_is_group_section (sec->owner, sec))
     return !(os != NULL
@@ -2349,6 +2349,12 @@ lang_add_section (lang_statement_list_type *ptr,
   if (strcmp (output->name, DISCARD_SECTION_NAME) == 0)
     discard = TRUE;
 
+  /* Discard the group descriptor sections when we're finally placing the
+     sections from within the group.  */
+  if ((section->flags & SEC_GROUP) == SEC_GROUP
+      && link_info.resolve_section_groups)
+    discard = TRUE;
+
   /* Discard debugging sections if we are stripping debugging
      information.  */
   if ((link_info.strip == strip_debugger || link_info.strip == strip_all)
@@ -2389,8 +2395,14 @@ lang_add_section (lang_statement_list_type *ptr,
      already been processed.  One reason to do this is that on pe
      format targets, .text$foo sections go into .text and it's odd
      to see .text with SEC_LINK_ONCE set.  */
-
-  if (!bfd_link_relocatable (&link_info))
+  if ((flags & (SEC_LINK_ONCE | SEC_GROUP)) == (SEC_LINK_ONCE | SEC_GROUP))
+    {
+      if (link_info.resolve_section_groups)
+        flags &= ~(SEC_LINK_ONCE | SEC_LINK_DUPLICATES | SEC_RELOC);
+      else
+        flags &= ~(SEC_LINK_DUPLICATES | SEC_RELOC);
+    }
+  else if (!bfd_link_relocatable (&link_info))
     flags &= ~(SEC_LINK_ONCE | SEC_LINK_DUPLICATES | SEC_RELOC);
 
   switch (output->sectype)
diff --git a/ld/ldlex.h b/ld/ldlex.h
index dac152b..5aa7f6b 100644
--- a/ld/ldlex.h
+++ b/ld/ldlex.h
@@ -146,6 +146,7 @@ enum option_values
   OPTION_PRINT_MEMORY_USAGE,
   OPTION_REQUIRE_DEFINED_SYMBOL,
   OPTION_ORPHAN_HANDLING,
+  OPTION_FORCE_GROUP_ALLOCATION,
 };
 
 /* The initial parser states.  */
diff --git a/ld/ldlex.l b/ld/ldlex.l
index acba1a2..ba618ec 100644
--- a/ld/ldlex.l
+++ b/ld/ldlex.l
@@ -274,6 +274,7 @@ V_IDENTIFIER [*?.$_a-zA-Z\[\]\-\!\^\\]([*?.$_a-zA-Z0-9\[\]\-\!\^\\]|::)*
 <BOTH,SCRIPT>"CREATE_OBJECT_SYMBOLS"	{ RTOKEN(CREATE_OBJECT_SYMBOLS);}
 <BOTH,SCRIPT>"CONSTRUCTORS"		{ RTOKEN( CONSTRUCTORS);}
 <BOTH,SCRIPT>"FORCE_COMMON_ALLOCATION"	{ RTOKEN(FORCE_COMMON_ALLOCATION);}
+<BOTH,SCRIPT>"FORCE_GROUP_ALLOCATION"	{ RTOKEN(FORCE_GROUP_ALLOCATION);}
 <BOTH,SCRIPT>"INHIBIT_COMMON_ALLOCATION" { RTOKEN(INHIBIT_COMMON_ALLOCATION);}
 <BOTH,SCRIPT>"SECTIONS"			{ RTOKEN(SECTIONS);}
 <BOTH,SCRIPT>"INSERT"			{ RTOKEN(INSERT_K);}
diff --git a/ld/ldmain.c b/ld/ldmain.c
index 2b3a591..ee5ab11 100644
--- a/ld/ldmain.c
+++ b/ld/ldmain.c
@@ -386,6 +386,12 @@ main (int argc, char **argv)
       info_msg ("\n==================================================\n");
     }
 
+  if (command_line.force_group_allocation
+      || !bfd_link_relocatable (&link_info))
+    link_info.resolve_section_groups = TRUE;
+  else
+    link_info.resolve_section_groups = FALSE;
+
   if (command_line.print_output_format)
     info_msg ("%s\n", lang_get_output_target ());
 
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 0b7d497..95c7e59 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -112,6 +112,9 @@ static const struct ld_option ld_options[] =
     'd', NULL, N_("Force common symbols to be defined"), ONE_DASH },
   { {"dp", no_argument, NULL, 'd'},
     '\0', NULL, NULL, ONE_DASH },
+  { {"force-group-allocation", no_argument, NULL,
+     OPTION_FORCE_GROUP_ALLOCATION},
+    '\0', NULL, N_("Force group members out of groups"), TWO_DASHES },
   { {"entry", required_argument, NULL, 'e'},
     'e', N_("ADDRESS"), N_("Set start address"), TWO_DASHES },
   { {"export-dynamic", no_argument, NULL, OPTION_EXPORT_DYNAMIC},
@@ -767,6 +770,9 @@ parse_args (unsigned argc, char **argv)
 	case 'd':
 	  command_line.force_common_definition = TRUE;
 	  break;
+        case OPTION_FORCE_GROUP_ALLOCATION:
+          command_line.force_group_allocation = TRUE;
+          break;
 	case OPTION_DEFSYM:
 	  lex_string = optarg;
 	  lex_redirect (optarg, "--defsym", ++defsym_count);
diff --git a/ld/testsuite/ld-elf/group11.d b/ld/testsuite/ld-elf/group11.d
new file mode 100644
index 0000000..245cf440
--- /dev/null
+++ b/ld/testsuite/ld-elf/group11.d
@@ -0,0 +1,6 @@
+#source: group1a.s
+#source: group1b.s
+#ld: -r --force-group-allocation
+#readelf: -g
+
+There are no section groups in this file.
diff --git a/ld/testsuite/ld-elf/group12.d b/ld/testsuite/ld-elf/group12.d
new file mode 100644
index 0000000..3fa7be8
--- /dev/null
+++ b/ld/testsuite/ld-elf/group12.d
@@ -0,0 +1,6 @@
+#source: group1a.s
+#source: group1b.s
+#ld: -r -T group12.ld
+#readelf: -g
+
+There are no section groups in this file.
diff --git a/ld/testsuite/ld-elf/group12.ld b/ld/testsuite/ld-elf/group12.ld
new file mode 100644
index 0000000..4a36ee5
--- /dev/null
+++ b/ld/testsuite/ld-elf/group12.ld
@@ -0,0 +1,14 @@
+FORCE_GROUP_ALLOCATION
+
+PHDRS
+{
+  header PT_PHDR PHDRS ;
+  image  PT_LOAD PHDRS;
+}
+
+SECTIONS
+{
+  . = 0x1000;
+  .text : { *(.text) *(.rodata.brlt) } :image :header
+  /DISCARD/ : { *(.dropme) *(.reginfo) *(.MIPS.abiflags) }
+}