[binutils-gdb/binutils-2_29-branch] ld: Early detection of orphans we know will be discarded

[Andrew Burgess <aburgess at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=dbb8f8b80b108dd60ab51c3e482c9c0865408b68

commit dbb8f8b80b108dd60ab51c3e482c9c0865408b68
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Thu Aug 17 11:29:04 2017 +0100

    ld: Early detection of orphans we know will be discarded
    
    When processing an orphan section we first call lang_place_orphans, this
    function handles a few sections for which the behaviour is known COMMON
    sections, or sections marked as SEC_EXCLUDE.
    
    Any orphans that are not handled in lang_place_orphans are passed on to
    ldlang_place_orphan, this is where we decide where to put the orphan,
    and then call lang_add_section to perform the actual orphan placement.
    
    We previously had a larger set of checks at the start of the function
    lang_add_section to discard some sections that we _knew_ should not be
    added into the output file, this was where .group sections (in a final
    link) and .debug* sections (with --strip-debug) were dropped.
    
    The problem with dropping these sections at the lang_add_section stage
    is that a user might also be using --orphan-handling=error to prevent
    orphans.  If they are then they should not be get errors about sections
    that we know will be discarded, and which are not mentioned in the
    linker script.
    
    The solution proposed in this patch is to move the "will this section be
    discarded" check into a separate function, and use this in
    lang_place_orphans to have the early discard phase discard sections that
    we know should not be included in the output file.
    
    ld/ChangeLog:
    
    	PR 21961
    	* ldlang.c (lang_discard_section_p): New function.
    	(lang_add_section): Checks moved out into new function, which is
    	now called.
    	(lang_place_orphans): Call lang_discard_section_p instead of
    	duplicating some of the checks from lang_add_section.
    	* testsuite/ld-elf/orphan-11.d: New file.
    	* testsuite/ld-elf/orphan-11.ld: New file.
    	* testsuite/ld-elf/orphan-11.s: New file.
    	* testsuite/ld-elf/orphan-12.d: New file.
    	* testsuite/ld-elf/orphan-12.s: New file.

Diff:
---
 ld/ChangeLog                     | 14 ++++++++++++
 ld/ldlang.c                      | 46 +++++++++++++++++++++++++++-------------
 ld/testsuite/ld-elf/orphan-11.d  |  9 ++++++++
 ld/testsuite/ld-elf/orphan-11.ld | 16 ++++++++++++++
 ld/testsuite/ld-elf/orphan-11.s  | 11 ++++++++++
 ld/testsuite/ld-elf/orphan-12.d  |  9 ++++++++
 ld/testsuite/ld-elf/orphan-12.s  |  8 +++++++
 7 files changed, 98 insertions(+), 15 deletions(-)

diff --git a/ld/ChangeLog b/ld/ChangeLog
index aeee2c8..c806a53 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,17 @@
+2017-08-17  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	PR 21961
+	* ldlang.c (lang_discard_section_p): New function.
+	(lang_add_section): Checks moved out into new function, which is
+	now called.
+	(lang_place_orphans): Call lang_discard_section_p instead of
+	duplicating some of the checks from lang_add_section.
+	* testsuite/ld-elf/orphan-11.d: New file.
+	* testsuite/ld-elf/orphan-11.ld: New file.
+	* testsuite/ld-elf/orphan-11.s: New file.
+	* testsuite/ld-elf/orphan-12.d: New file.
+	* testsuite/ld-elf/orphan-12.s: New file.
+
 2017-08-23  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-gc/pr19161.d: Don't xfail hppa.
diff --git a/ld/ldlang.c b/ld/ldlang.c
index 726bc8e..4ce0f51 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -2274,6 +2274,34 @@ section_already_linked (bfd *abfd, asection *sec, void *data)
     bfd_section_already_linked (abfd, sec, &link_info);
 }
 
+
+/* Returns true if SECTION is one we know will be discarded based on its
+   section flags, otherwise returns false.  */
+
+static bfd_boolean
+lang_discard_section_p (asection *section)
+{
+  bfd_boolean discard;
+  flagword flags = section->flags;
+
+  /* Discard sections marked with SEC_EXCLUDE.  */
+  discard = (flags & SEC_EXCLUDE) != 0;
+
+  /* Discard the group descriptor sections when we're finally placing the
+     sections from within the group.  */
+  if ((flags & SEC_GROUP) != 0
+      && 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)
+      && (flags & SEC_DEBUGGING) != 0)
+    discard = TRUE;
+
+  return discard;
+}
+
 /* The wild routines.
 
    These expand statements like *(.text) and foo.o to a list of
@@ -2295,26 +2323,14 @@ lang_add_section (lang_statement_list_type *ptr,
   lang_input_section_type *new_section;
   bfd *abfd = link_info.output_bfd;
 
-  /* Discard sections marked with SEC_EXCLUDE.  */
-  discard = (flags & SEC_EXCLUDE) != 0;
+  /* Is this section one we know should be discarded?  */
+  discard = lang_discard_section_p (section);
 
   /* Discard input sections which are assigned to a section named
      DISCARD_SECTION_NAME.  */
   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)
-      && (flags & SEC_DEBUGGING) != 0)
-    discard = TRUE;
-
   if (discard)
     {
       if (section->output_section == NULL)
@@ -6411,7 +6427,7 @@ lang_place_orphans (void)
 
 	      if (file->flags.just_syms)
 		bfd_link_just_syms (file->the_bfd, s, &link_info);
-	      else if ((s->flags & SEC_EXCLUDE) != 0)
+	      else if (lang_discard_section_p (s))
 		s->output_section = bfd_abs_section_ptr;
 	      else if (strcmp (s->name, "COMMON") == 0)
 		{
diff --git a/ld/testsuite/ld-elf/orphan-11.d b/ld/testsuite/ld-elf/orphan-11.d
new file mode 100644
index 0000000..3daefba
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-11.d
@@ -0,0 +1,9 @@
+#source: orphan-11.s
+#ld: -T orphan-11.ld --orphan-handling=error
+#objdump: -wh
+#notarget: d30v-* dlx-* fr30-* frv-* ft32-* i860-* i960-* iq2000-* mn10200-* moxie-* ms1-* msp430-* mt-* pj-*
+
+#...
+  . \.text .*
+  . \.data .*
+#pass
diff --git a/ld/testsuite/ld-elf/orphan-11.ld b/ld/testsuite/ld-elf/orphan-11.ld
new file mode 100644
index 0000000..74c7789
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-11.ld
@@ -0,0 +1,16 @@
+SECTIONS
+{
+  . = SIZEOF_HEADERS;
+  .text : { *(.text .text.*) }
+  .data : { *(.data .data.*) }
+  .bss : { *(.bss .bss.*) *(COMMON) }
+  .sbss : { *(.sbss .sbss.*) }
+  .note : { *(.note .note.*) }
+  .rela : { *(.rela .rela.*) }
+  .rel : { *(.rel .rel.*) }
+
+  /DISCARD/ : {
+            *(.reginfo) *(.MIPS.abiflags) *(.trampolines) *(.iplt*)
+            *(.note*) *(.got*) *(.igot*) *(.*.attributes) *(.*.info)
+            *(.pdr) "linker stubs*"(*)  }
+}
diff --git a/ld/testsuite/ld-elf/orphan-11.s b/ld/testsuite/ld-elf/orphan-11.s
new file mode 100644
index 0000000..3d7961b
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-11.s
@@ -0,0 +1,11 @@
+	.section .text.foo,"axG",%progbits,foo_group
+	.word 0
+
+	.section .data.foo,"waG",%progbits,foo_group
+	.word 1
+
+	.section .text, "ax"
+	.word 0
+
+	.section .data, "wa"
+	.word 1
diff --git a/ld/testsuite/ld-elf/orphan-12.d b/ld/testsuite/ld-elf/orphan-12.d
new file mode 100644
index 0000000..71a8c93
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-12.d
@@ -0,0 +1,9 @@
+#source: orphan-12.s
+#ld: -T orphan-11.ld --strip-debug --orphan-handling=error
+#objdump: -wh
+#notarget: d30v-* dlx-* fr30-* frv-* ft32-* i860-* i960-* iq2000-* mn10200-* moxie-* ms1-* msp430-* mt-* pj-*
+
+#...
+  . \.text .*
+  . \.data .*
+#pass
diff --git a/ld/testsuite/ld-elf/orphan-12.s b/ld/testsuite/ld-elf/orphan-12.s
new file mode 100644
index 0000000..f9cbcf7
--- /dev/null
+++ b/ld/testsuite/ld-elf/orphan-12.s
@@ -0,0 +1,8 @@
+	.section .debug_info, "",%progbits
+	.word 0
+
+	.section .text, "ax"
+	.word 0
+
+	.section .data, "wa"
+	.word 1