OpenE2K/binutils-gdb
12
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

PR 21847, Don't default PowerPC64 to --plt-localentry

Browse Source 
The big comment in ppc64_elf_tls_setup says why.  I've also added some
code to the bfd linker that catches the -lpthread -lc symbol
differences and disable generation of optimized call stubs even when
--plt-localentry is activated.  Gold doesn't yet have that.

	PR 21847
bfd/
	* elf64-ppc.c (struct ppc_link_hash_entry): Add non_zero_localentry.
	(ppc64_elf_merge_symbol): Set non_zero_localentry.
	(is_elfv2_localentry0): Test non_zero_localentry.
	(ppc64_elf_tls_setup): Default to --no-plt-localentry.
gold/
	* powerpc.cc (Target_powerpc::scan_relocs): Default to
	--no-plt-localentry.
ld/
	* ld.texinfo (plt-localentry): Document.
This commit is contained in:
Alan Modra 2017-07-29 12:33:35 +09:30
parent ef080e7ed4
commit 8b5f1ed877
6 changed files with 56 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
bfd/ChangeLog
View File

@ -1,3 +1,11 @@
2017-07-29 Alan Modra <amodra@gmail.com>
PR 21847
* elf64-ppc.c (struct ppc_link_hash_entry): Add non_zero_localentry.
(ppc64_elf_merge_symbol): Set non_zero_localentry.
(is_elfv2_localentry0): Test non_zero_localentry.
(ppc64_elf_tls_setup): Default to --no-plt-localentry.
2017-07-28 Andreas Krebbel <krebbel@linux.vnet.ibm.com>
* elf32-s390.c (elf_s390_finish_dynamic_sections): Add NULL

27
bfd/elf64-ppc.c
View File

@ -4013,6 +4013,10 @@ struct ppc_link_hash_entry
with non-standard calling convention. */
unsigned int save_res:1;
/* Set if a duplicate symbol with non-zero localentry is detected,
even when the duplicate symbol does not provide a definition. */
unsigned int non_zero_localentry:1;
/* Contexts in which symbol is used in the GOT (or TOC).
TLS_GD .. TLS_EXPLICIT bits are or'd into the mask as the
corresponding relocs are encountered during check_relocs.
@ -5021,7 +5025,7 @@ ppc64_elf_merge_symbol_attribute (struct elf_link_hash_entry *h,
static bfd_boolean
ppc64_elf_merge_symbol (struct elf_link_hash_entry *h,
const Elf_Internal_Sym *isym ATTRIBUTE_UNUSED,
const Elf_Internal_Sym *isym,
asection **psec ATTRIBUTE_UNUSED,
bfd_boolean newdef ATTRIBUTE_UNUSED,
bfd_boolean olddef ATTRIBUTE_UNUSED,
@ -5029,6 +5033,8 @@ ppc64_elf_merge_symbol (struct elf_link_hash_entry *h,
const asection *oldsec ATTRIBUTE_UNUSED)
{
((struct ppc_link_hash_entry *) h)->fake = 0;
if ((STO_PPC64_LOCAL_MASK & isym->st_other) != 0)
((struct ppc_link_hash_entry *) h)->non_zero_localentry = 1;
return TRUE;
}
@ -6335,6 +6341,7 @@ is_elfv2_localentry0 (struct elf_link_hash_entry *h)
&& h->type == STT_FUNC
&& h->root.type == bfd_link_hash_defined
&& (STO_PPC64_LOCAL_MASK & h->other) == 0
&& !((struct ppc_link_hash_entry *) h)->non_zero_localentry
&& is_ppc64_elf (h->root.u.def.section->owner)
&& abiversion (h->root.u.def.section->owner) >= 2);
}
@ -8349,10 +8356,22 @@ ppc64_elf_tls_setup (struct bfd_link_info *info)
else if (!htab->do_multi_toc)
htab->params->no_multi_toc = 1;
/* Default to --no-plt-localentry, as this option can cause problems
with symbol interposition. For example, glibc libpthread.so and
libc.so duplicate many pthread symbols, with a fallback
implementation in libc.so. In some cases the fallback does more
work than the pthread implementation. __pthread_condattr_destroy
is one such symbol: the libpthread.so implementation is
localentry:0 while the libc.so implementation is localentry:8.
An app that "cleverly" uses dlopen to only load necessary
libraries at runtime may omit loading libpthread.so when not
running multi-threaded, which then results in the libc.so
fallback symbols being used and ld.so complaining. Now there
are workarounds in ld (see non_zero_localentry) to detect the
pthread situation, but that may not be the only case where
--plt-localentry can cause trouble. */
if (htab->params->plt_localentry0 < 0)
htab->params->plt_localentry0
= elf_link_hash_lookup (&htab->elf, "GLIBC_2.26",
FALSE, FALSE, FALSE) != NULL;
htab->params->plt_localentry0 = 0;
htab->tls_get_addr = ((struct ppc_link_hash_entry *)
elf_link_hash_lookup (&htab->elf, ".__tls_get_addr",

6
gold/ChangeLog
View File

@ -1,3 +1,9 @@
2017-07-29 Alan Modra <amodra@gmail.com>
PR 21847
* powerpc.cc (Target_powerpc::scan_relocs): Default to
--no-plt-localentry.
2017-07-28 H.J. Lu <hongjiu.lu@intel.com>
PR gold/21857

2
gold/powerpc.cc
View File

@ -7660,8 +7660,6 @@ Target_powerpc<size, big_endian>::scan_relocs(
{
if (parameters->options().user_set_plt_localentry())
plt_localentry0 = parameters->options().plt_localentry();
else
plt_localentry0 = symtab->lookup("GLIBC_2.26", NULL) != NULL;
}
this->plt_localentry0_ = plt_localentry0;
this->plt_localentry0_init_ = true;

4
ld/ChangeLog
View File

@ -1,3 +1,7 @@
2017-07-29 Alan Modra <amodra@gmail.com>
* ld.texinfo (plt-localentry): Document.
2017-07-28 Andrew Burgess <andrew.burgess@embecosm.com>
* ldgram.y (ldgram_had_keep): Make static.

15
ld/ld.texinfo
View File

@ -7600,6 +7600,21 @@ barrier in the call stub, or use LD_BIND_NOW=1. By default, @code{ld}
looks for calls to commonly used functions that create threads, and if
seen, adds the necessary barriers. Use these options to change the
default behaviour.
@cindex PowerPC64 ELFv2 PLT localentry optimization
@kindex --plt-localentry
@kindex --no-plt-localentry
@item --plt-localentry
@itemx --no-localentry
ELFv2 functions with localentry:0 are those with a single entry point,
ie. global entry == local entry, and that have no requirement on r2
(the TOC/GOT pointer) or r12, and guarantee r2 is unchanged on return.
Such an external function can be called via the PLT without saving r2
or restoring it on return, avoiding a common load-hit-store for small
functions. The optimization is attractive, with up to 40% reduction
in execution time for a small function, but can result in symbol
interposition failures. Use with care. @option{--no-plt-localentry}
is the default.
@end table
@ifclear GENERIC