powerpc common-page-size

max-page-size only matters for demand paged executables or shared
libraries, and the ideal size is the largest value used by your
operating system.  Values larger than necessary just waste file space
and memory.  common-page-size also affects file and memory size,
trading a possible small increase in file size for a decrease in
memory size when the operating system is using a common-page-size
page.  With a powerpc max-page-size of 64k and common-page-size of 4k
many executables will use no more memory pages when the system page
size is 4k than an executable linked with -z max-page-size=0x1000,
yet will still run on a system using 64k pages.  However, when running
on a system using 64k pages relro protection will not be completely
effective.

Due to the relro problem, powerpc binutils has been using a default
common-page-size of 64k since 2014-12-18 (git commit 04c6a44c7),
leading to complaints about increased file and memory sizes.  People
not using relro do have a valid reason to complain..

So this patch introduces an extra back-end value to use as the default
for common-page-size when generating relro executables, and enables
the support for powerpc.  Non relro executables will now be generated
with a default common-page-size of 4k.

bfd/
	* elf-bfd.h (struct elf_backend_data): Add relropagesize.
	* elfxx-target.h (ELF_RELROPAGESIZE): Provide default and
	sanity test.
	(elfNN_bed): Init relropagesize.
	* bfd.c (bfd_emul_get_commonpagesize): Add boolean param to
	select relropagesize.
	* elf32-ppc.c (ELF_COMMONPAGESIZE): Define as 0x1000.
	(ELF_RELROPAGESIZE): Define as ELF_MAXPAGESIZE.
	(ELF_MINPAGESIZE): Don't define.
	* elf64-ppc.c (ELF_COMMONPAGESIZE): Define as 0x1000.
	(ELF_RELROPAGESIZE): Define as ELF_MAXPAGESIZE.
	* bfd-in2.h: Regenerate.
ld/
	* ldmain.c (main): Move config.maxpagesize and
	config.commonpagesize initialization to..
	* ldemul.c (after_parse_default): ..here.
	* testsuite/ld-powerpc/ppc476-shared.d: Pass -z common-page-size.
	* testsuite/ld-powerpc/ppc476-shared2.d: Likewise.

bfd/ChangeLog

@@ -1,3 +1,18 @@
+2018-04-14  Alan Modra  <amodra@gmail.com>
+
+	* elf-bfd.h (struct elf_backend_data): Add relropagesize.
+	* elfxx-target.h (ELF_RELROPAGESIZE): Provide default and
+	sanity test.
+	(elfNN_bed): Init relropagesize.
+	* bfd.c (bfd_emul_get_commonpagesize): Add boolean param to
+	select relropagesize.
+	* elf32-ppc.c (ELF_COMMONPAGESIZE): Define as 0x1000.
+	(ELF_RELROPAGESIZE): Define as ELF_MAXPAGESIZE.
+	(ELF_MINPAGESIZE): Don't define.
+	* elf64-ppc.c (ELF_COMMONPAGESIZE): Define as 0x1000.
+	(ELF_RELROPAGESIZE): Define as ELF_MAXPAGESIZE.
+	* bfd-in2.h: Regenerate.
+
 2018-04-14  Alan Modra  <amodra@gmail.com>
 
 	* elf32-ppc.c (ELF_MAXPAGESIZE, ELF_COMMONPAGESIZE): Don't depend

bfd/bfd-in2.h

@@ -7251,7 +7251,7 @@ bfd_vma bfd_emul_get_maxpagesize (const char *);
 
 void bfd_emul_set_maxpagesize (const char *, bfd_vma);
 
-bfd_vma bfd_emul_get_commonpagesize (const char *);
+bfd_vma bfd_emul_get_commonpagesize (const char *, bfd_boolean);
 
 void bfd_emul_set_commonpagesize (const char *, bfd_vma);
 

bfd/bfd.c

@@ -2137,7 +2137,7 @@ FUNCTION
 	bfd_emul_get_commonpagesize
 
 SYNOPSIS
-	bfd_vma bfd_emul_get_commonpagesize (const char *);
+	bfd_vma bfd_emul_get_commonpagesize (const char *, bfd_boolean);
 
 DESCRIPTION
 	Returns the common page size, in bytes, as determined by
@@ -2148,15 +2148,22 @@ RETURNS
 */
 
 bfd_vma
-bfd_emul_get_commonpagesize (const char *emul)
+bfd_emul_get_commonpagesize (const char *emul, bfd_boolean relro)
 {
   const bfd_target *target;
 
   target = bfd_find_target (emul, NULL);
   if (target != NULL
       && target->flavour == bfd_target_elf_flavour)
-    return xvec_get_elf_backend_data (target)->commonpagesize;
+    {
+      const struct elf_backend_data *bed;
 
+      bed = xvec_get_elf_backend_data (target);
+      if (relro)
+	return bed->relropagesize;
+      else
+	return bed->commonpagesize;
+    }
   return 0;
 }
 

bfd/elf-bfd.h

@@ -864,6 +864,9 @@ struct elf_backend_data
   /* The common page size for this backend.  */
   bfd_vma commonpagesize;
 
+  /* The value of commonpagesize to use when -z relro for this backend.  */
+  bfd_vma relropagesize;
+
   /* The BFD flags applied to sections created for dynamic linking.  */
   flagword dynamic_sec_flags;
 

bfd/elf32-ppc.c

@@ -11390,8 +11390,8 @@ ppc_elf_finish_dynamic_sections (bfd *output_bfd,
 #define ELF_TARGET_ID		PPC32_ELF_DATA
 #define ELF_MACHINE_CODE	EM_PPC
 #define ELF_MAXPAGESIZE		0x10000
-#define ELF_COMMONPAGESIZE	0x10000
+#define ELF_COMMONPAGESIZE	0x1000
-#define ELF_MINPAGESIZE		0x1000
+#define ELF_RELROPAGESIZE	ELF_MAXPAGESIZE
 #define elf_info_to_howto	ppc_elf_info_to_howto
 
 #ifdef  EM_CYGNUS_POWERPC

bfd/elf64-ppc.c

@@ -64,7 +64,8 @@ static bfd_vma opd_entry_value
 #define ELF_TARGET_ID		PPC64_ELF_DATA
 #define ELF_MACHINE_CODE	EM_PPC64
 #define ELF_MAXPAGESIZE		0x10000
-#define ELF_COMMONPAGESIZE	0x10000
+#define ELF_COMMONPAGESIZE	0x1000
+#define ELF_RELROPAGESIZE	ELF_MAXPAGESIZE
 #define elf_info_to_howto	ppc64_elf_info_to_howto
 
 #define elf_backend_want_got_sym 0

bfd/elfxx-target.h

@@ -367,6 +367,10 @@
 #define ELF_COMMONPAGESIZE ELF_MAXPAGESIZE
 #endif
 
+#ifndef ELF_RELROPAGESIZE
+#define ELF_RELROPAGESIZE ELF_COMMONPAGESIZE
+#endif
+
 #ifndef ELF_MINPAGESIZE
 #define ELF_MINPAGESIZE ELF_COMMONPAGESIZE
 #endif
@@ -374,9 +378,15 @@
 #if ELF_COMMONPAGESIZE > ELF_MAXPAGESIZE
 # error ELF_COMMONPAGESIZE > ELF_MAXPAGESIZE
 #endif
+#if ELF_RELROPAGESIZE > ELF_MAXPAGESIZE
+# error ELF_RELROPAGESIZE > ELF_MAXPAGESIZE
+#endif
 #if ELF_MINPAGESIZE > ELF_COMMONPAGESIZE
 # error ELF_MINPAGESIZE > ELF_COMMONPAGESIZE
 #endif
+#if ELF_MINPAGESIZE > ELF_RELROPAGESIZE
+# error ELF_MINPAGESIZE > ELF_RELROPAGESIZE
+#endif
 
 #ifndef ELF_DYNAMIC_SEC_FLAGS
 /* Note that we set the SEC_IN_MEMORY flag for these sections.  */
@@ -757,6 +767,7 @@ static struct elf_backend_data elfNN_bed =
   ELF_MAXPAGESIZE,		/* maxpagesize */
   ELF_MINPAGESIZE,		/* minpagesize */
   ELF_COMMONPAGESIZE,		/* commonpagesize */
+  ELF_RELROPAGESIZE,		/* commonpagesize to use with -z relro */
   ELF_DYNAMIC_SEC_FLAGS,	/* dynamic_sec_flags */
   elf_backend_arch_data,
   elf_info_to_howto,

ld/ChangeLog

@@ -1,3 +1,11 @@
+2018-04-14  Alan Modra  <amodra@gmail.com>
+
+	* ldmain.c (main): Move config.maxpagesize and
+	config.commonpagesize initialization to..
+	* ldemul.c (after_parse_default): ..here.
+	* testsuite/ld-powerpc/ppc476-shared.d: Pass -z common-page-size.
+	* testsuite/ld-powerpc/ppc476-shared2.d: Likewise.
+
 2018-04-14  Alan Modra  <amodra@gmail.com>
 
 	* emulparams/elf32ppcwindiss.sh: Rewrite to use elf32ppc.sh.

ld/ldemul.c

@@ -225,6 +225,11 @@ after_parse_default (void)
       if (!is_vma)
 	ldlang_add_undef (entry_symbol.name, entry_from_cmdline);
     }
+  if (config.maxpagesize == 0)
+    config.maxpagesize = bfd_emul_get_maxpagesize (default_target);
+  if (config.commonpagesize == 0)
+    config.commonpagesize = bfd_emul_get_commonpagesize (default_target,
+							 link_info.relro);
 }
 
 void

ld/ldmain.c

@@ -305,8 +305,6 @@ main (int argc, char **argv)
   emulation = get_emulation (argc, argv);
   ldemul_choose_mode (emulation);
   default_target = ldemul_choose_target (argc, argv);
-  config.maxpagesize = bfd_emul_get_maxpagesize (default_target);
-  config.commonpagesize = bfd_emul_get_commonpagesize (default_target);
   lang_init ();
   ldexp_init ();
   ldemul_before_parse ();

ld/testsuite/ld-powerpc/ppc476-shared.d

@@ -1,6 +1,6 @@
 #source: ppc476-shared.s
 #as: -a32
-#ld: -melf32ppc -q -shared --ppc476-workaround -T ppc476-shared.lnk
+#ld: -melf32ppc -q -shared -z common-page-size=0x10000 --ppc476-workaround -T ppc476-shared.lnk
 #objdump: -dr
 #target: powerpc*-*-*
 

ld/testsuite/ld-powerpc/ppc476-shared2.d

@@ -1,6 +1,6 @@
 #source: ppc476-shared.s
 #as: -a32
-#ld: -melf32ppc -shared --ppc476-workaround -T ppc476-shared.lnk
+#ld: -melf32ppc -shared -z common-page-size=0x10000 --ppc476-workaround -T ppc476-shared.lnk
 #objdump: -R
 #target: powerpc*-*-*