[Patch] AIX/ld fix section alignment in linker script

[Tristan Gingold]

Hi,

currently the default AIX linker script uses PPC segment boundary to align .text and .data
In fact, this is never used as is, because gcc specs always adds -bpT:0x10000000 -bpD:0x20000000 to the linker command.

As a result, the SIZEOF_HEADERS will be added to the via of .text (see aix.em):
	  etree_type *t;

	  t = exp_binop ('+',
			 exp_intop (val),
			 exp_nameop (SIZEOF_HEADERS, NULL));
	  t = exp_binop ('&',
			 exp_binop ('+', t, exp_intop (31)),
			 exp_intop (~(bfd_vma) 31));
	  lang_section_start (".text", t, NULL);

and the vma of .text will match its file offset (modulo the page size).

So why not making that by default too ?

Things are going worse for .data, because although aix.em tries to keep the file offset in the vma:
	  t = exp_binop ('+',
			 exp_intop (val),
			 exp_binop ('&',
				    exp_nameop (NAME, "."),
				    exp_intop (0xfff)));
	  t = exp_binop ('&',
			 exp_binop ('+', t, exp_intop (31)),
			 exp_intop (~(bfd_vma) 31));
	  lang_section_start (".data", t, NULL);

it doesn't work because of '. = ALIGN (0x10000000)'.  As a result the file offset is forgotten, contrary to the native linker.

(This issue was somewhat difficult to find because the AIX kernel still accept such image.  I have no idea of the performance impact of these badly offsetted images)

Ok for trunk ?

Tristan.

ld/
2011-10-21  Tristan Gingold  <gingold@adacore.com>

	* scripttempl/aix.sc: Consider header size for .text and .data
	alignment.

diff --git a/ld/scripttempl/aix.sc b/ld/scripttempl/aix.sc
index d592dbe..adc5de6 100644
--- a/ld/scripttempl/aix.sc
+++ b/ld/scripttempl/aix.sc
@@ -11,7 +11,7 @@ SECTIONS
 {
   .pad 0 : { *(.pad) }
 
-  . = 0x10000000;
+  . = ALIGN (0x10000000 + SIZEOF_HEADERS, 32);
   .text ${RELOCATING-0} : {
     ${RELOCATING+PROVIDE (_text = .);}
     *(.text)
@@ -24,7 +24,8 @@ SECTIONS
     *(.tb)
     ${RELOCATING+PROVIDE (_etext = .);}
   }
-  . = ALIGN (0x10000000);
+
+  . = ALIGN (ALIGN (0x10000000) + (. & 0xfff), 32);
   .data . : {
     ${RELOCATING+PROVIDE (_data = .);}
     *(.data)