powerpc64: Fix calls when r2 is not used [BZ #26173]

Teach the linker that __mcount_internal, __sigjmp_save_symbol,
__syscall_error and __GI_exit do not use r2, so that it does not need to
recover r2 after the call.

Test at configure time if the assembler supports @notoc and define
USE_PPC64_NOTOC.

config.h.in

@@ -20,6 +20,9 @@
 /* On powerpc64, use overlapping .opd entries.  */
 #undef  USE_PPC64_OVERLAPPING_OPD
 
+/* On powerpc64, use @notoc.  */
+#undef  USE_PPC64_NOTOC
+
 /* Define if _Unwind_Find_FDE should be exported from glibc.  */
 #undef  EXPORT_UNWIND_FIND_FDE
 

sysdeps/powerpc/powerpc64/configure

@@ -31,3 +31,31 @@ if test x$libc_cv_overlapping_opd = xyes; then
   $as_echo "#define USE_PPC64_OVERLAPPING_OPD 1" >>confdefs.h
 
 fi
+
+# @notoc started to be supported in GNU Binutils 2.31.
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if the assembler supports @notoc" >&5
+$as_echo_n "checking if the assembler supports @notoc... " >&6; }
+if ${libc_cv_ppc64_notoc+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+	       cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+void foo (void) {asm("b foo@notoc");}
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  libc_cv_ppc64_notoc=yes
+else
+  libc_cv_ppc64_notoc=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ppc64_notoc" >&5
+$as_echo "$libc_cv_ppc64_notoc" >&6; }
+if test x$libc_cv_ppc64_notoc = xyes; then :
+  $as_echo "#define USE_PPC64_NOTOC 1" >>confdefs.h
+
+fi

sysdeps/powerpc/powerpc64/configure.ac

@@ -21,3 +21,14 @@ rm -f conftest.c conftest.s
 if test x$libc_cv_overlapping_opd = xyes; then
   AC_DEFINE(USE_PPC64_OVERLAPPING_OPD)
 fi
+
+# @notoc started to be supported in GNU Binutils 2.31.
+AC_CACHE_CHECK([if the assembler supports @notoc],
+	       libc_cv_ppc64_notoc, [
+	       AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+void foo (void) {asm("b foo@notoc");}
+		  ])],
+		  [libc_cv_ppc64_notoc=yes],
+		  [libc_cv_ppc64_notoc=no])])
+AS_IF([test x$libc_cv_ppc64_notoc = xyes],
+      [AC_DEFINE(USE_PPC64_NOTOC)])

sysdeps/powerpc/powerpc64/ppc-mcount.S

@@ -29,7 +29,7 @@ ENTRY(_mcount)
 	cfi_adjust_cfa_offset (FRAME_MIN_SIZE)
 	cfi_offset (lr, FRAME_LR_SAVE)
 	ld		 r3, FRAME_LR_SAVE(r11)
-	bl		 JUMPTARGET(__mcount_internal)
+	bl		 JUMPTARGET (NOTOC (__mcount_internal))
 #ifndef SHARED
 	nop
 #endif

sysdeps/powerpc/powerpc64/setjmp-common.S

@@ -217,7 +217,7 @@ L(no_vmx):
 	li	r3,0
 	blr
 #elif defined SHARED
-	b	JUMPTARGET (__sigjmp_save_symbol)
+	b	JUMPTARGET (NOTOC (__sigjmp_save_symbol))
 #else
 	mflr	r0
 	std	r0,FRAME_LR_SAVE(r1)

sysdeps/powerpc/powerpc64/sysdep.h

@@ -278,7 +278,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
 
 #ifdef SHARED
 #define TAIL_CALL_SYSCALL_ERROR \
-    b JUMPTARGET(__syscall_error)
+    b JUMPTARGET (NOTOC (__syscall_error))
 #else
 /* Static version might be linked into a large app with a toc exceeding
    64k.  We can't put a toc adjusting stub on a plain branch, so can't
@@ -366,6 +366,12 @@ LT_LABELSUFFIX(name,_name_end): ; \
 	lwz	rOUT,0(rOUT)
 #endif
 
+#ifdef USE_PPC64_NOTOC
+# define NOTOC(l) l@notoc
+#else
+# define NOTOC(l) l
+#endif
+
 #else /* !__ASSEMBLER__ */
 
 #if _CALL_ELF != 2

sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S

@@ -160,7 +160,7 @@ L(exitcode):
 	li    r3,-1
 L(do_exit):
 #ifdef SHARED
-	b     JUMPTARGET(__GI_exit);
+	b     JUMPTARGET (NOTOC (__GI_exit));
 #else
 	b     JUMPTARGET(exit);
 	nop