PPC64_OPT_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 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.  The TOC pointer load-hit-store is a major
reason why calls to small functions that need no register saves, or
with shrink-wrap, no register saves on a fast path, are slow on
powerpc64le.

To be safe, this optimization needs ld.so support to check that the
run-time matches link-time function implementation.  If a function
in a shared library with st_other localentry non-zero is called
without saving and restoring r2, r2 will be trashed on return, leading
to segfaults.  For that reason the optimization does not happen for
weak functions since a weak definition is a fairly solid hint that the
function will likely be overridden.  I'm also not enabling the
optimization by default unless glibc-2.26 is detected, which should
have the ld.so checks implemented.

bfd/
	* elf64-ppc.c (struct ppc_link_hash_table): Add has_plt_localentry0.
	(ppc64_elf_merge_symbol_attribute): Merge localentry bits from
	dynamic objects.
	(is_elfv2_localentry0): New function.
	(ppc64_elf_tls_setup): Default params->plt_localentry0.
	(plt_stub_size): Adjust size for tls_get_addr_opt stub.
	(build_tls_get_addr_stub): Use a simpler stub when r2 is not saved.
	(ppc64_elf_size_stubs): Leave stub_type as ppc_stub_plt_call for
	optimized localentry:0 stubs.
	(ppc64_elf_build_stubs): Save r2 in ELFv2 __glink_PLTresolve.
	(ppc64_elf_relocate_section): Leave nop unchanged for optimized
	localentry:0 stubs.
	(ppc64_elf_finish_dynamic_sections): Set PPC64_OPT_LOCALENTRY in
	DT_PPC64_OPT.
	* elf64-ppc.h (struct ppc64_elf_params): Add plt_localentry0.
include/
	* elf/ppc64.h (PPC64_OPT_LOCALENTRY): Define.
ld/
	* emultempl/ppc64elf.em (params): Init plt_localentry0 field.
	(enum ppc64_opt): New, replacing OPTION_* defines.  Add
	OPTION_PLT_LOCALENTRY, and OPTION_NO_PLT_LOCALENTRY.
	(PARSE_AND_LIST_*): Support --plt-localentry and --no-plt-localentry.
	* testsuite/ld-powerpc/elfv2so.d: Update.
	* testsuite/ld-powerpc/powerpc.exp (TLS opt 5): Use --no-plt-localentry.
	* testsuite/ld-powerpc/tlsopt5.d: Update.

5 files changed, 57 insertions, 26 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index da03e3a..e2d5496 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,13 @@
+2017-06-01  Alan Modra  <amodra@gmail.com>
+
+	* emultempl/ppc64elf.em (params): Init plt_localentry0 field.
+	(enum ppc64_opt): New, replacing OPTION_* defines.  Add
+	OPTION_PLT_LOCALENTRY, and OPTION_NO_PLT_LOCALENTRY.
+	(PARSE_AND_LIST_*): Support --plt-localentry and --no-plt-localentry.
+	* testsuite/ld-powerpc/elfv2so.d: Update.
+	* testsuite/ld-powerpc/powerpc.exp (TLS opt 5): Use --no-plt-localentry.
+	* testsuite/ld-powerpc/tlsopt5.d: Update.
+
 2017-05-31  Alan Modra  <amodra@gmail.com>
 
 	* emultempl/ppc64elf.em (plt-static-chain help): Fix quoting.
diff --git a/ld/emultempl/ppc64elf.em b/ld/emultempl/ppc64elf.em
index f1d5274..58cb798 100644
--- a/ld/emultempl/ppc64elf.em
+++ b/ld/emultempl/ppc64elf.em
@@ -38,7 +38,7 @@ static struct ppc64_elf_params params = { NULL,
 					  &ppc_layout_sections_again,
 					  1, -1, 0,
 					  ${DEFAULT_PLT_STATIC_CHAIN-0}, -1, 0,
-					  0, -1, -1, 0};
+					  -1, 0, -1, -1, 0};
 
 /* Fake input file for stubs.  */
 static lang_input_statement_type *stub_file;
@@ -683,27 +683,32 @@ fi
 # parse_args and list_options functions.
 #
 PARSE_AND_LIST_PROLOGUE=${PARSE_AND_LIST_PROLOGUE}'
-#define OPTION_STUBGROUP_SIZE		321
-#define OPTION_PLT_STATIC_CHAIN		(OPTION_STUBGROUP_SIZE + 1)
-#define OPTION_NO_PLT_STATIC_CHAIN	(OPTION_PLT_STATIC_CHAIN + 1)
-#define OPTION_PLT_THREAD_SAFE		(OPTION_NO_PLT_STATIC_CHAIN + 1)
-#define OPTION_NO_PLT_THREAD_SAFE	(OPTION_PLT_THREAD_SAFE + 1)
-#define OPTION_PLT_ALIGN		(OPTION_NO_PLT_THREAD_SAFE + 1)
-#define OPTION_NO_PLT_ALIGN		(OPTION_PLT_ALIGN + 1)
-#define OPTION_STUBSYMS			(OPTION_NO_PLT_ALIGN + 1)
-#define OPTION_NO_STUBSYMS		(OPTION_STUBSYMS + 1)
-#define OPTION_SAVRES			(OPTION_NO_STUBSYMS + 1)
-#define OPTION_NO_SAVRES		(OPTION_SAVRES + 1)
-#define OPTION_DOTSYMS			(OPTION_NO_SAVRES + 1)
-#define OPTION_NO_DOTSYMS		(OPTION_DOTSYMS + 1)
-#define OPTION_NO_TLS_OPT		(OPTION_NO_DOTSYMS + 1)
-#define OPTION_TLS_GET_ADDR_OPT		(OPTION_NO_TLS_OPT + 1)
-#define OPTION_NO_TLS_GET_ADDR_OPT	(OPTION_TLS_GET_ADDR_OPT + 1)
-#define OPTION_NO_OPD_OPT		(OPTION_NO_TLS_GET_ADDR_OPT + 1)
-#define OPTION_NO_TOC_OPT		(OPTION_NO_OPD_OPT + 1)
-#define OPTION_NO_MULTI_TOC		(OPTION_NO_TOC_OPT + 1)
-#define OPTION_NO_TOC_SORT		(OPTION_NO_MULTI_TOC + 1)
-#define OPTION_NON_OVERLAPPING_OPD	(OPTION_NO_TOC_SORT + 1)
+enum ppc64_opt
+{
+  OPTION_STUBGROUP_SIZE = 321,
+  OPTION_PLT_STATIC_CHAIN,
+  OPTION_NO_PLT_STATIC_CHAIN,
+  OPTION_PLT_THREAD_SAFE,
+  OPTION_NO_PLT_THREAD_SAFE,
+  OPTION_PLT_ALIGN,
+  OPTION_NO_PLT_ALIGN,
+  OPTION_PLT_LOCALENTRY,
+  OPTION_NO_PLT_LOCALENTRY,
+  OPTION_STUBSYMS,
+  OPTION_NO_STUBSYMS,
+  OPTION_SAVRES,
+  OPTION_NO_SAVRES,
+  OPTION_DOTSYMS,
+  OPTION_NO_DOTSYMS,
+  OPTION_NO_TLS_OPT,
+  OPTION_TLS_GET_ADDR_OPT,
+  OPTION_NO_TLS_GET_ADDR_OPT,
+  OPTION_NO_OPD_OPT,
+  OPTION_NO_TOC_OPT,
+  OPTION_NO_MULTI_TOC,
+  OPTION_NO_TOC_SORT,
+  OPTION_NON_OVERLAPPING_OPD
+};
 '
 
 PARSE_AND_LIST_LONGOPTS=${PARSE_AND_LIST_LONGOPTS}'
@@ -714,6 +719,8 @@ PARSE_AND_LIST_LONGOPTS=${PARSE_AND_LIST_LONGOPTS}'
   { "no-plt-thread-safe", no_argument, NULL, OPTION_NO_PLT_THREAD_SAFE },
   { "plt-align", optional_argument, NULL, OPTION_PLT_ALIGN },
   { "no-plt-align", no_argument, NULL, OPTION_NO_PLT_ALIGN },
+  { "plt-localentry", optional_argument, NULL, OPTION_PLT_LOCALENTRY },
+  { "no-plt-localentry", no_argument, NULL, OPTION_NO_PLT_LOCALENTRY },
   { "emit-stub-syms", no_argument, NULL, OPTION_STUBSYMS },
   { "no-emit-stub-syms", no_argument, NULL, OPTION_NO_STUBSYMS },
   { "dotsyms", no_argument, NULL, OPTION_DOTSYMS },
@@ -760,6 +767,12 @@ PARSE_AND_LIST_OPTIONS=${PARSE_AND_LIST_OPTIONS}'
   --no-plt-align              Dont'\''t align individual PLT call stubs.\n"
 		   ));
   fprintf (file, _("\
+  --plt-localentry            Optimize calls to ELFv2 localentry:0 functions.\n"
+		   ));
+  fprintf (file, _("\
+  --no-plt-localentry         Don'\''t optimize ELFv2 calls.\n"
+		   ));
+  fprintf (file, _("\
   --emit-stub-syms            Label linker stubs with a symbol.\n"
 		   ));
   fprintf (file, _("\
@@ -852,6 +865,14 @@ PARSE_AND_LIST_ARGS_CASES=${PARSE_AND_LIST_ARGS_CASES}'
       params.plt_stub_align = 0;
       break;
 
+    case OPTION_PLT_LOCALENTRY:
+      params.plt_localentry0 = 1;
+      break;
+
+    case OPTION_NO_PLT_LOCALENTRY:
+      params.plt_localentry0 = 0;
+      break;
+
     case OPTION_STUBSYMS:
       params.emit_stub_syms = 1;
       break;
diff --git a/ld/testsuite/ld-powerpc/elfv2so.d b/ld/testsuite/ld-powerpc/elfv2so.d
index d6f0b7d..f3962ac 100644
--- a/ld/testsuite/ld-powerpc/elfv2so.d
+++ b/ld/testsuite/ld-powerpc/elfv2so.d
@@ -57,6 +57,7 @@ Disassembly of section \.text:
 .*:	(7c 08 02 a6|a6 02 08 7c) 	mflr    r0
 .*:	(42 9f 00 05|05 00 9f 42) 	bcl     .*
 .*:	(7d 68 02 a6|a6 02 68 7d) 	mflr    r11
+.*:	(18 00 41 f8|f8 41 00 18) 	std     r2,24\(r1\)
 .*:	(e8 4b ff f0|f0 ff 4b e8) 	ld      r2,-16\(r11\)
 .*:	(7c 08 03 a6|a6 03 08 7c) 	mtlr    r0
 .*:	(7d 8b 60 50|50 60 8b 7d) 	subf    r12,r11,r12
@@ -67,7 +68,6 @@ Disassembly of section \.text:
 .*:	(7d 89 03 a6|a6 03 89 7d) 	mtctr   r12
 .*:	(e9 6b 00 08|08 00 6b e9) 	ld      r11,8\(r11\)
 .*:	(4e 80 04 20|20 04 80 4e) 	bctr
-.*:	(60 00 00 00|00 00 00 60) 	nop
 
 .* <f3@plt>:
 .*:	(4b ff ff c8|c8 ff ff 4b) 	b       .* <__glink_PLTresolve>
diff --git a/ld/testsuite/ld-powerpc/powerpc.exp b/ld/testsuite/ld-powerpc/powerpc.exp
index 5350235..f12e413 100644
--- a/ld/testsuite/ld-powerpc/powerpc.exp
+++ b/ld/testsuite/ld-powerpc/powerpc.exp
@@ -210,7 +210,7 @@ set ppc64elftests {
       "tlsopt4"}
     {"TLS DLL" "-shared -melf64ppc --version-script tlsdll.ver" "" "-a64" {tlsdll.s}
      {} "tlsdll.so"}
-    {"TLS opt 5" "-melf64ppc --gc-sections tmpdir/tlsdll.so" "" "-a64"  {tlsopt5.s}
+    {"TLS opt 5" "-melf64ppc --gc-sections --no-plt-localentry tmpdir/tlsdll.so" "" "-a64"  {tlsopt5.s}
      {{objdump -dr tlsopt5.d}}
       "tlsopt5"}
     {"sym@tocbase" "-shared -melf64ppc" "" "-a64" {symtocbase-1.s symtocbase-2.s}
diff --git a/ld/testsuite/ld-powerpc/tlsopt5.d b/ld/testsuite/ld-powerpc/tlsopt5.d
index 7b17130..b356a2e 100644
--- a/ld/testsuite/ld-powerpc/tlsopt5.d
+++ b/ld/testsuite/ld-powerpc/tlsopt5.d
@@ -1,6 +1,6 @@
 #source: tlsopt5.s
 #as: -a64
-#ld: --gc-sections tlsdll.so
+#ld: --gc-sections --no-plt-localentry tlsdll.so
 #objdump: -dr
 #target: powerpc64*-*-*
 
@@ -38,6 +38,7 @@ Disassembly of section \.text:
 .*:	(a6 02 08 7c|7c 08 02 a6) 	mflr    r0
 .*:	(05 00 9f 42|42 9f 00 05) 	bcl     .*
 .*:	(a6 02 68 7d|7d 68 02 a6) 	mflr    r11
+.*:	(18 00 41 f8|f8 41 00 18) 	std     r2,24\(r1\)
 .*:	(f0 ff 4b e8|e8 4b ff f0) 	ld      r2,-16\(r11\)
 .*:	(a6 03 08 7c|7c 08 03 a6) 	mtlr    r0
 .*:	(50 60 8b 7d|7d 8b 60 50) 	subf    r12,r11,r12
@@ -48,7 +49,6 @@ Disassembly of section \.text:
 .*:	(a6 03 89 7d|7d 89 03 a6) 	mtctr   r12
 .*:	(08 00 6b e9|e9 6b 00 08) 	ld      r11,8\(r11\)
 .*:	(20 04 80 4e|4e 80 04 20) 	bctr
-.*:	(00 00 00 60|60 00 00 00) 	nop
 
 0000000010000390 <__tls_get_addr_opt@plt>:
 .*:	(c8 ff ff 4b|4b ff ff c8) 	b       .*