[PATCH, rs6000, 5/6] Backport patch to align .toc section

[PATCH, rs6000, 5/6] Backport patch to align .toc section

[Bill Schmidt]

Hi,

Alan added code to have GCC align the .toc section in GCC 7, aligning to
four bytes for 32-bit mode, and 8 bytes for 64-bit mode.  This is normally
unnecessary since alignment of the .toc has historically been handled by
the standard linker script.  However, people using non-standard toolchains
can still run into problems, so as a courtesy this is now done by the
compiler as well.

We've recently seen this encountered using an out-of-service compiler, and
would like to prevent any more occurrences by people finding interesting
ways to avoid the standard toolchain.  Thus I'd like to backport Alan's
patch to GCC 5 and 6.  Alan, please review as well to be sure I didn't
miss any release-specific differences.

Bootstrapped and tested on powerpc64le-linux-gnu with no regressions.
Are these backports ok?

Thanks,
Bill


2017-07-23  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	Backport from mainline r235874
	2016-05-04  Alan Modra  <amodra@gmail.com>

	* config/rs6000/rs6000.c (rs6000_elf_output_toc_section_asm_op):
	Align .toc.


Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	(revision 250426)
+++ gcc/config/rs6000/rs6000.c	(working copy)
@@ -32699,8 +32699,8 @@ rs6000_elf_output_toc_section_asm_op (const void *
     {
       if (!toc_initialized)
 	{
-	  toc_initialized = 1;
 	  fprintf (asm_out_file, "%s\n", TOC_SECTION_ASM_OP);
+	  ASM_OUTPUT_ALIGN (asm_out_file, TARGET_64BIT ? 3 : 2);
 	  (*targetm.asm_out.internal_label) (asm_out_file, "LCTOC", 0);
 	  fprintf (asm_out_file, "\t.tc ");
 	  ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1[TC],");
@@ -32708,8 +32708,10 @@ rs6000_elf_output_toc_section_asm_op (const void *
 	  fprintf (asm_out_file, "\n");
 
 	  fprintf (asm_out_file, "%s\n", MINIMAL_TOC_SECTION_ASM_OP);
+	  ASM_OUTPUT_ALIGN (asm_out_file, TARGET_64BIT ? 3 : 2);
 	  ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1");
 	  fprintf (asm_out_file, " = .+32768\n");
+	  toc_initialized = 1;
 	}
       else
 	fprintf (asm_out_file, "%s\n", MINIMAL_TOC_SECTION_ASM_OP);
@@ -32716,12 +32718,20 @@ rs6000_elf_output_toc_section_asm_op (const void *
     }
   else if ((DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2)
 	   && !TARGET_RELOCATABLE)
-    fprintf (asm_out_file, "%s\n", TOC_SECTION_ASM_OP);
+    {
+      fprintf (asm_out_file, "%s\n", TOC_SECTION_ASM_OP);
+      if (!toc_initialized)
+	{
+	  ASM_OUTPUT_ALIGN (asm_out_file, TARGET_64BIT ? 3 : 2);
+	  toc_initialized = 1;
+	}
+    }
   else
     {
       fprintf (asm_out_file, "%s\n", MINIMAL_TOC_SECTION_ASM_OP);
       if (!toc_initialized)
 	{
+	  ASM_OUTPUT_ALIGN (asm_out_file, TARGET_64BIT ? 3 : 2);
 	  ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1");
 	  fprintf (asm_out_file, " = .+32768\n");
 	  toc_initialized = 1;

Re: [PATCH, rs6000, 5/6] Backport patch to align .toc section

[Segher Boessenkool]

Hi Bill,

On Sun, Jul 23, 2017 at 12:07:37PM -0500, Bill Schmidt wrote:
> Alan added code to have GCC align the .toc section in GCC 7, aligning to
> four bytes for 32-bit mode, and 8 bytes for 64-bit mode.  This is normally
> unnecessary since alignment of the .toc has historically been handled by
> the standard linker script.  However, people using non-standard toolchains
> can still run into problems, so as a courtesy this is now done by the
> compiler as well.
> 
> We've recently seen this encountered using an out-of-service compiler, and
> would like to prevent any more occurrences by people finding interesting
> ways to avoid the standard toolchain.  Thus I'd like to backport Alan's
> patch to GCC 5 and 6.  Alan, please review as well to be sure I didn't
> miss any release-specific differences.
> 
> Bootstrapped and tested on powerpc64le-linux-gnu with no regressions.
> Are these backports ok?

Sure, if Alan is happy with it, please commit.


Segher


> 2017-07-23  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
> 
> 	Backport from mainline r235874
> 	2016-05-04  Alan Modra  <amodra@gmail.com>
> 
> 	* config/rs6000/rs6000.c (rs6000_elf_output_toc_section_asm_op):
> 	Align .toc.