[PATCH] PR ld/21334: Always assign dynsym indices even in static binaries

["Maciej W. Rozycki" <macro at imgtec dot com>]

Complement commit e17b0c351f0b ("MIPS/BFD: Respect the ELF gABI dynamic 
symbol table sort requirement") and correct an inconsistency in dynamic 
symbol accounting data causing an assertion failure in the MIPS backend:

ld: BFD (GNU Binutils) 2.28.51.20170330 assertion fail ../../binutils-gdb/bfd/elfxx-mips.c:3860

in the course of making a GOT entry in a static binary to satisfy a GOT 
relocation present in input, due to the local dynamic symbol count not 
having been established.

To do so move the call to `_bfd_elf_link_renumber_dynsyms' outside a 
check for dynamic sections to have been created, so that the function 
always assigns dynsym indices and initializes associated data, even for 
static binaries.

	bfd/
	PR ld/21334
	* elflink.c (bfd_elf_size_dynsym_hash_dynstr): Always call
	`_bfd_elf_link_renumber_dynsyms'.

	ld/
	PR ld/21334
	* testsuite/ld-mips-elf/pr21334.dd: New test.
	* testsuite/ld-mips-elf/pr21334.gd: New test.
	* testsuite/ld-mips-elf/pr21334.ld: New test linker script.
	* testsuite/ld-mips-elf/pr21334.s: New test source.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new tests.
---
 No regressions against the usual targets.

 Calling `_bfd_elf_link_renumber_dynsyms' unconditionally has also been 
verified to some extent to be safe by Debian across their targets, as a 
side effect of `_bfd_elf_link_renumber_dynsyms' always being called when 
section GC has been enabled with `--gc-sections', as it has been the case 
with some of their packages, which according to James's statement posted 
with the PR includes KDE/Qt and some other packages.

 OK for master and 2.28?

 NB one of the test cases added relies on MIPS static GOT dump support 
in `readelf' just posted, so firstly the order of patches will have to 
be maintained and secondly I'll remove it from the 2.28 backport.

  Maciej

binutils-bfd-elf-always-dynsym-renumber.diff
Index: binutils/bfd/elflink.c
===================================================================
--- binutils.orig/bfd/elflink.c	2017-04-10 23:11:21.572119928 +0100
+++ binutils/bfd/elflink.c	2017-04-11 02:45:59.328420966 +0100
@@ -6778,6 +6778,8 @@ bfd_boolean
 bfd_elf_size_dynsym_hash_dynstr (bfd *output_bfd, struct bfd_link_info *info)
 {
   const struct elf_backend_data *bed;
+  unsigned long section_sym_count;
+  bfd_size_type dynsymcount;
 
   if (!is_elf_hash_table (info->hash))
     return TRUE;
@@ -6785,24 +6787,29 @@ bfd_elf_size_dynsym_hash_dynstr (bfd *ou
   bed = get_elf_backend_data (output_bfd);
   (*bed->elf_backend_init_index_section) (output_bfd, info);
 
+  /* Assign dynsym indices.  In a shared library we generate a section
+     symbol for each output section, which come first.  Next come all
+     of the back-end allocated local dynamic syms, followed by the rest
+     of the global symbols.
+
+     We always do this step even if dynamic sections have not been made,
+     because backends may need symbol accounting data produced here,
+     e.g. the MIPS backend uses dynamic symbol counts to lay out GOT,
+     which will be produced in the presence of GOT relocations even in
+     static binaries (holding fixed data in that case, to satisfy those
+     relocations).  */
+
+  dynsymcount = _bfd_elf_link_renumber_dynsyms (output_bfd, info,
+						&section_sym_count);
+
   if (elf_hash_table (info)->dynamic_sections_created)
     {
       bfd *dynobj;
       asection *s;
-      bfd_size_type dynsymcount;
-      unsigned long section_sym_count;
       unsigned int dtagcount;
 
       dynobj = elf_hash_table (info)->dynobj;
 
-      /* Assign dynsym indicies.  In a shared library we generate a
-	 section symbol for each output section, which come first.
-	 Next come all of the back-end allocated local dynamic syms,
-	 followed by the rest of the global symbols.  */
-
-      dynsymcount = _bfd_elf_link_renumber_dynsyms (output_bfd, info,
-						    &section_sym_count);
-
       /* Work out the size of the symbol version section.  */
       s = bfd_get_linker_section (dynobj, ".gnu.version");
       BFD_ASSERT (s != NULL);
Index: binutils/ld/testsuite/ld-mips-elf/mips-elf.exp
===================================================================
--- binutils.orig/ld/testsuite/ld-mips-elf/mips-elf.exp	2017-04-10 23:11:20.401635333 +0100
+++ binutils/ld/testsuite/ld-mips-elf/mips-elf.exp	2017-04-11 02:47:43.596728893 +0100
@@ -1130,3 +1130,13 @@ if { $linux_gnu } {
 		  "export-$class-ref"]]
     }
 }
+
+# PR ld/21334 GOT relocation in static binary test.
+run_ld_link_tests [list \
+    [list \
+	"PR ld/21233 MIPS GOT16 relocation in static binary" \
+	"$abi_ldflags(o32) -e foo -T pr21334.ld" "" "$abi_asflags(o32)" \
+	{pr21334.s} \
+	{{objdump {-d --prefix-addresses} pr21334.dd} \
+	 {readelf -A pr21334.gd}} \
+	"pr21334"]]
Index: binutils/ld/testsuite/ld-mips-elf/pr21334.dd
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ binutils/ld/testsuite/ld-mips-elf/pr21334.dd	2017-04-11 02:47:43.603859887 +0100
@@ -0,0 +1,10 @@
+.*: +file format .*mips.*
+
+Disassembly of section \.text:
+[0-9a-f]+ <[^>]*> lui	gp,0x1
+[0-9a-f]+ <[^>]*> addiu	gp,gp,-32736
+[0-9a-f]+ <[^>]*> addu	gp,gp,t9
+[0-9a-f]+ <[^>]*> lw	v0,-32744\(gp\)
+[0-9a-f]+ <[^>]*> jr	ra
+[0-9a-f]+ <[^>]*> addiu	v0,v0,4
+	\.\.\.
Index: binutils/ld/testsuite/ld-mips-elf/pr21334.gd
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ binutils/ld/testsuite/ld-mips-elf/pr21334.gd	2017-04-11 02:47:43.629240183 +0100
@@ -0,0 +1,11 @@
+Static GOT:
+ Canonical gp value: 00008020
+
+ Reserved entries:
+   Address     Access    Value
+  00000030 -32752\(gp\) 00000000
+  00000034 -32748\(gp\) 80000000
+
+ Local entries:
+   Address     Access    Value
+  00000038 -32744\(gp\) 00000000
Index: binutils/ld/testsuite/ld-mips-elf/pr21334.ld
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ binutils/ld/testsuite/ld-mips-elf/pr21334.ld	2017-04-11 02:47:43.646400289 +0100
@@ -0,0 +1,9 @@
+SECTIONS
+{
+  .text : { *(.text) }
+  HIDDEN (_gp = ALIGN (16) + 0x7ff0);
+  .got : { *(.got) }
+  .symtab : { *(.symtab) }
+  .strtab : { *(.strtab) }
+  /DISCARD/ : { *(*) }
+}
Index: binutils/ld/testsuite/ld-mips-elf/pr21334.s
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ binutils/ld/testsuite/ld-mips-elf/pr21334.s	2017-04-11 02:47:43.663515875 +0100
@@ -0,0 +1,20 @@
+	.abicalls
+	.text
+	.set	noreorder
+	.globl	foo
+	.ent	foo
+foo:
+	.frame	$sp, 0, $31
+	.mask	0x00000000, 0
+	.fmask	0x00000000, 0
+	.cpload	$25
+	lw	$2, %got(bar)($28)
+	jr	$31
+	 addiu	$2, $2, 4
+	.end	foo
+	.weak	bar
+	.hidden	bar
+
+# Force some (non-delay-slot) zero bytes, to make 'objdump' print ...
+	.align	4, 0
+	.space	16