PowerPC64 does not require an executable stack for many of the usual
reasons other common targets need one, eg. nested function call
trampolines just put a function descriptor on the stack rather than
a small code sequence. Also, shortly after the linux kernel
implemented non-exec stacks for ppc64, the default was changed to
non-exec unless a PT_GNU_STACK header with PF_X was present. See
http://ozlabs.org/pipermail/linuxppc64-dev/2005-April/003891.html.
So there is really no need for .note.GNU-stack or PT_GNU_STACK on
ppc64 unless you want to mark an object file or executable as needing
exec stack. For that reason, I changed gcc-4.x to omit
.note.GNU-stack on ppc64. See
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21098. However, for some
reason Redhat changed their version of gcc to mark all ppc64 object
files with .note.GNU-stack. This presents a problem when mixing
objects created by different compilers, because the linker requires
that if some object file has .note.GNU-stack, then they all must, and
if one file is missing .note.GNU-stack it is assumed to be exec stack.

I think that for ppc64 it would make more sense to assume that a file
without the .note.GNU-stack marker is non-exec stack. This will allow
mixing of Redhat object files with mainline gcc, and is in fact the
correct default for ppc64.

* elf-bfd.h (struct elf_backend_data): Add default_execstack.
* elflink.c (bfd_elf_size_dynamic_sections): Heed default_execstack.
* elfxx-target.h (elf_backend_default_execstack): Define to 1.
(elfNN_bed): Init new field.
* elf64-ppc.c (elf_backend_default_execstack): Define to 0.

Index: bfd/elf-bfd.h
===================================================================
RCS file: /cvs/src/src/bfd/elf-bfd.h,v
retrieving revision 1.226
diff -u -p -r1.226 elf-bfd.h
--- bfd/elf-bfd.h 5 Feb 2007 19:50:12 -0000 1.226
+++ bfd/elf-bfd.h 19 Feb 2007 00:17:23 -0000
@@ -1106,10 +1106,17 @@ struct elf_backend_data
unsigned can_refcount : 1;
unsigned want_got_sym : 1;
unsigned want_dynbss : 1;
- /* Targets which do not support physical addressing often require
- that the p_paddr field in the section header to be set to zero.
- This field indicates whether this behavior is required. */
+
+ /* Targets which do not support physical addressing often require
+ that the p_paddr field in the section header to be set to zero.
+ This field indicates whether this behavior is required. */
unsigned want_p_paddr_set_to_zero : 1;
+
+ /* True if an object file lacking a .note.GNU-stack section
+ should be assumed to be requesting exec stack. At least one
+ other file in the link needs to have a .note.GNU-stack section
+ for a PT_GNU_STACK segment to be created. */
+ unsigned default_execstack : 1;
};

/* Information stored for each BFD section in an ELF file. This
Index: bfd/elflink.c
===================================================================
RCS file: /cvs/src/src/bfd/elflink.c,v
retrieving revision 1.250
diff -u -p -r1.250 elflink.c
--- bfd/elflink.c 14 Feb 2007 14:15:52 -0000 1.250
+++ bfd/elflink.c 19 Feb 2007 00:18:44 -0000
@@ -5237,6 +5237,7 @@ bfd_elf_size_dynamic_sections (bfd *outp
if (!is_elf_hash_table (info->hash))
return TRUE;

+ bed = get_elf_backend_data (output_bfd);
elf_tdata (output_bfd)->relro = info->relro;
if (info->execstack)
elf_tdata (output_bfd)->stack_flags = PF_R | PF_W | PF_X;
@@ -5263,7 +5264,7 @@ bfd_elf_size_dynamic_sections (bfd *outp
exec = PF_X;
notesec = s;
}
- else
+ else if (bed->default_execstack)
exec = PF_X;
}
if (notesec)
@@ -5284,7 +5285,6 @@ bfd_elf_size_dynamic_sections (bfd *outp

/* The backend may have to create some sections regardless of whether
we're dynamic or not. */
- bed = get_elf_backend_data (output_bfd);
if (bed->elf_backend_always_size_sections
&& ! (*bed->elf_backend_always_size_sections) (output_bfd, info))
return FALSE;
Index: bfd/elfxx-target.h
===================================================================
RCS file: /cvs/src/src/bfd/elfxx-target.h,v
retrieving revision 1.102
diff -u -p -r1.102 elfxx-target.h
--- bfd/elfxx-target.h 1 Feb 2007 05:35:58 -0000 1.102
+++ bfd/elfxx-target.h 19 Feb 2007 00:18:53 -0000
@@ -103,6 +103,9 @@
#ifndef elf_backend_want_p_paddr_set_to_zero
#define elf_backend_want_p_paddr_set_to_zero 0
#endif
+#ifndef elf_backend_default_execstack
+#define elf_backend_default_execstack 1
+#endif

#define bfd_elfNN_bfd_debug_info_start bfd_void
#define bfd_elfNN_bfd_debug_info_end bfd_void
@@ -683,7 +686,8 @@ static struct elf_backend_data elfNN_bed
elf_backend_can_refcount,
elf_backend_want_got_sym,
elf_backend_want_dynbss,
- elf_backend_want_p_paddr_set_to_zero
+ elf_backend_want_p_paddr_set_to_zero,
+ elf_backend_default_execstack
};

/* Forward declaration for use when initialising alternative_target field. */
Index: bfd/elf64-ppc.c
===================================================================
RCS file: /cvs/src/src/bfd/elf64-ppc.c,v
retrieving revision 1.257
diff -u -p -r1.257 elf64-ppc.c
--- bfd/elf64-ppc.c 13 Feb 2007 01:53:02 -0000 1.257
+++ bfd/elf64-ppc.c 19 Feb 2007 00:35:35 -0000
@@ -73,6 +73,7 @@ static bfd_vma opd_entry_value
#define elf_backend_can_gc_sections 1
#define elf_backend_can_refcount 1
#define elf_backend_rela_normal 1
+#define elf_backend_default_execstack 0

#define bfd_elf64_mkobject ppc64_elf_mkobject
#define bfd_elf64_bfd_reloc_type_lookup ppc64_elf_reloc_type_lookup
@@ -1197,7 +1198,7 @@ static reloc_howto_type ppc64_elf_howto_

/* Like R_PPC64_PLTGOT16, but for instructions with a DS field. */
/* FIXME: R_PPC64_PLTGOT16_DS not implemented. */
- HOWTO (R_PPC64_PLTGOT16_DS, /* type */
+ HOWTO (R_PPC64_PLTGOT16_DS, /* type */
0, /* rightshift */
1, /* size (0 = byte, 1 = short, 2 = long) */
16, /* bitsize */