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ppc32 profiling of shared libx
- From: Alan Modra <amodra at gmail dot com>
- To: binutils at sourceware dot org
- Date: Sun, 14 Aug 2011 18:46:20 +0930
- Subject: ppc32 profiling of shared libx
Profiling doesn't work at all on ppc32 -msecure-plt shared libraries,
and not reliably on PIEs. The problem is that a ppc32 PIC PLT call
stub uses r30 (GOT pointer) to load the function address from the PLT,
r30 being set up in the function prologue, but _mcount is called
before the function prologue. So chances are good that r30 will be
pointing to the executable GOT when trying to call _mcount in a shared
lib function. A similary problem can occur in a PIE if a shared lib
calls a function in the executable.
The proper fix is to move _mcount to libc_nonshared.a for ppc32, but
until everyone has this fix in their libc we can just force bss-plt.
* elf32-ppc.c (ppc_elf_select_plt_layout): Force bss-plt when
shared and call to _mcount will go via plt.
Index: bfd/elf32-ppc.c
===================================================================
RCS file: /cvs/src/src/bfd/elf32-ppc.c,v
retrieving revision 1.300
diff -u -p -r1.300 elf32-ppc.c
--- bfd/elf32-ppc.c 5 Aug 2011 02:24:08 -0000 1.300
+++ bfd/elf32-ppc.c 14 Aug 2011 03:49:01 -0000
@@ -4256,8 +4256,27 @@ ppc_elf_select_plt_layout (bfd *output_b
if (htab->plt_type == PLT_UNSET)
{
+ struct elf_link_hash_entry *h;
+
if (plt_style == PLT_OLD)
htab->plt_type = PLT_OLD;
+ else if (info->shared
+ && htab->elf.dynamic_sections_created
+ && (h = elf_link_hash_lookup (&htab->elf, "_mcount",
+ FALSE, FALSE, TRUE)) != NULL
+ && (h->type == STT_FUNC
+ || h->needs_plt)
+ && h->ref_regular
+ && !(SYMBOL_CALLS_LOCAL (info, h)
+ || (ELF_ST_VISIBILITY (h->other) != STV_DEFAULT
+ && h->root.type == bfd_link_hash_undefweak)))
+ {
+ /* Profiling of shared libs (and pies) is not supported with
+ secure plt, because ppc32 does profiling before a
+ function prologue and a secure plt pic call stubs needs
+ r30 to be set up. */
+ htab->plt_type = PLT_OLD;
+ }
else
{
bfd *ibfd;
@@ -4285,7 +4304,13 @@ ppc_elf_select_plt_layout (bfd *output_b
}
}
if (htab->plt_type == PLT_OLD && plt_style == PLT_NEW)
- info->callbacks->einfo (_("%P: bss-plt forced due to %B\n"), htab->old_bfd);
+ {
+ if (htab->old_bfd != NULL)
+ info->callbacks->einfo (_("%P: bss-plt forced due to %B\n"),
+ htab->old_bfd);
+ else
+ info->callbacks->einfo (_("%P: bss-plt forced by profiling\n"));
+ }
BFD_ASSERT (htab->plt_type != PLT_VXWORKS);
--
Alan Modra
Australia Development Lab, IBM