[PATCHv2] Fix float128 IFUNC relocations on ppc64le [BZ #21707]

["Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>]

Changes since version 1:

 - Added a testcase.  This is now validating both statically and
   dynamically linked executables.
 - Fixed an issue in the $(foreach ..) in sysdeps/powerpc/powerpc64le/Makefile.
 - Added a comment to csu/libc-start.c
 - Added a comment to csu/libc-tls.c

-- 8< --

The patch proposed by Peter Bergner [1] to libgc in order to fix
[BZ #21707] adds a dependency on a symbol provided by the loader,
forcing the loader to be linked to tests after libgcc was linked.

It also requires to read the thread pointer during IRELA relocations.

Tested on powerpc, powerpc64, powerpc64le, s390x and x86_64.

[1] https://sourceware.org/ml/libc-alpha/2017-06/msg01383.html

2017-07-08  Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>

	[BZ #21707]
	* csu/libc-start.c (LIBC_START_MAIN): Perform IREL{,A}
	relocations after initializing the TCB on statically linked
	executables..
	* csu/libc-tls.c (__libc_setup_tls): Add a comment about
	IREL{,A} relocations.
	* elf/Makefile (tests-static-normal): Add tst-tlsifunc-static.
	(tests): Add tst-tlsifunc.
	* elf/tst-tlsifunc.c: New file.
	* elf/tst-tlsifunc-static.c: Likewise.
	* sysdeps/powerpc/powerpc64le/Makefile (f128-loader-link): New
	variable.
	[$(subdir) = math] (test-float128% test-ifloat128%): Force
	linking to the loader after linking to libgcc.
	[$(subdir) = wcsmbs stdlib] (bug-strtod bug-strtod2 bug-strtod2)
	(tst-strtod-round tst-wcstod-round tst-strtod6 tst-strrom)
	(tst-strfrom-locale strfrom-skeleton): Likewise.
---
 csu/libc-start.c                     | 11 +++---
 csu/libc-tls.c                       |  2 ++
 elf/Makefile                         |  5 +--
 elf/tst-tlsifunc-static.c            | 19 +++++++++++
 elf/tst-tlsifunc.c                   | 66 ++++++++++++++++++++++++++++++++++++
 sysdeps/powerpc/powerpc64le/Makefile | 10 ++++++
 6 files changed, 107 insertions(+), 6 deletions(-)
 create mode 100644 elf/tst-tlsifunc-static.c
 create mode 100644 elf/tst-tlsifunc.c

diff --git a/csu/libc-start.c b/csu/libc-start.c
index c2dd159..84b7f99 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -188,12 +188,15 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
 
   ARCH_INIT_CPU_FEATURES ();
 
-  /* Perform IREL{,A} relocations.  */
-  apply_irel ();
-
   /* The stack guard goes into the TCB, so initialize it early.  */
   __libc_setup_tls ();
 
+  /* Perform IREL{,A} relocations.
+     Note: the relocations must happen after TLS initialization so that
+     IFUNC resolvers can benefit from thread-local storage, e.g. powerpc's
+     hwcap and platform fields available in the TCB.  */
+  apply_irel ();
+
   /* Set up the stack checker's canary.  */
   uintptr_t stack_chk_guard = _dl_setup_stack_chk_guard (_dl_random);
 # ifdef THREAD_SET_STACK_GUARD
@@ -224,7 +227,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
   __pointer_chk_guard_local = pointer_chk_guard;
 # endif
 
-#endif
+#endif /* !SHARED  */
 
   /* Register the destructor of the dynamic linker if there is any.  */
   if (__glibc_likely (rtld_fini != NULL))
diff --git a/csu/libc-tls.c b/csu/libc-tls.c
index 3c897bf..2947912 100644
--- a/csu/libc-tls.c
+++ b/csu/libc-tls.c
@@ -101,6 +101,8 @@ init_static_tls (size_t memsz, size_t align)
   GL(dl_tls_static_nelem) = GL(dl_tls_max_dtv_idx);
 }
 
+/* Note: IREL{,A} relocations happen after TLS setup.  __libc_setup_tls has
+   to guarantee that it won't use STT_GNU_IFUNC.  */
 void
 __libc_setup_tls (void)
 {
diff --git a/elf/Makefile b/elf/Makefile
index 201b328..b603e89 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -147,12 +147,13 @@ tests-static-normal := tst-leaks1-static tst-array1-static tst-array5-static \
 	       tst-tlsalign-static tst-tlsalign-extern-static \
 	       tst-linkall-static tst-env-setuid tst-env-setuid-tunables
 tests-static-internal := tst-tls1-static tst-tls2-static \
-	       tst-ptrguard1-static tst-stackguard1-static
+	       tst-ptrguard1-static tst-stackguard1-static \
+	       tst-tlsifunc-static
 
 tests := tst-tls9 tst-leaks1 \
 	tst-array1 tst-array2 tst-array3 tst-array4 tst-array5 \
 	tst-auxv
-tests-internal := tst-tls1 tst-tls2 $(tests-static-internal)
+tests-internal := tst-tls1 tst-tls2 tst-tlsifunc $(tests-static-internal)
 tests-static := $(tests-static-normal) $(tests-static-internal)
 
 ifeq (yes,$(build-shared))
diff --git a/elf/tst-tlsifunc-static.c b/elf/tst-tlsifunc-static.c
new file mode 100644
index 0000000..e5313af
--- /dev/null
+++ b/elf/tst-tlsifunc-static.c
@@ -0,0 +1,19 @@
+/* Test if an executable can read from the TLS from an STT_GNU_IFUNC resolver.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "tst-tlsifunc.c"
diff --git a/elf/tst-tlsifunc.c b/elf/tst-tlsifunc.c
new file mode 100644
index 0000000..531d20f
--- /dev/null
+++ b/elf/tst-tlsifunc.c
@@ -0,0 +1,66 @@
+/* Test if an executable can read from the TLS from an STT_GNU_IFUNC resolver.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <libc-symbols.h>
+#include "tls-macros.h"
+
+__thread int bar;
+static int * bar_ptr = NULL;
+
+int foo (void);
+
+void
+init_foo (void)
+{
+  bar_ptr = TLS_GD (bar);
+}
+
+int
+my_foo (void)
+{
+  printf ("&bar = %p and bar_ptr = %p.\n", &bar, bar_ptr);
+  return bar_ptr != NULL;
+}
+
+__ifunc (foo, foo, my_foo, void, init_foo);
+
+static int
+do_test (void)
+{
+  int ret = 0;
+
+  if (foo ())
+    printf ("PASS: IFUNC resolver called once.\n");
+  else {
+    printf ("FAIL: IFUNC resolver not called once.\n");
+    ret = 1;
+  }
+
+  if (&bar == bar_ptr)
+    printf ("PASS: Address read from IFUNC resolver is correct.\n");
+  else {
+    printf ("FAIL: Address read from IFUNC resolver is incorrect.\n");
+    ret = 1;
+  }
+
+  return ret;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/powerpc/powerpc64le/Makefile b/sysdeps/powerpc/powerpc64le/Makefile
index bd8a82d..90a41b1 100644
--- a/sysdeps/powerpc/powerpc64le/Makefile
+++ b/sysdeps/powerpc/powerpc64le/Makefile
@@ -1,6 +1,11 @@
 # When building float128 we need to ensure -mfloat128 is
 # passed to all such object files.
 
+# libgcc requires __tcb_parse_hwcap_and_convert_at_platform when built with
+# a binary128 type.  That symbol is provided by the loader on dynamically
+# linked executables, forcing to link the loader after libgcc link.
+f128-loader-link = $(as-needed) $(elf-objpfx)ld.so $(no-as-needed)
+
 ifeq ($(subdir),math)
 # sqrtf128 requires emulation before POWER9.
 CPPFLAGS += -I../soft-fp
@@ -11,6 +16,8 @@ $(foreach suf,$(all-object-suffixes),%f128_r$(suf)): CFLAGS += -mfloat128
 $(objpfx)test-float128%.o $(objpfx)test-float128%.os: CFLAGS += -mfloat128
 $(objpfx)test-ifloat128%.o $(objpfx)test-ifloat128%.os: CFLAGS += -mfloat128
 CFLAGS-libm-test-support-float128.c += -mfloat128
+$(objpfx)test-float128% $(objpfx)test-ifloat128%: \
+  gnulib-tests += $(f128-loader-link)
 endif
 
 # Append flags to string <-> _Float128 routines.
@@ -24,6 +31,9 @@ CFLAGS-tst-strtod6.c += -mfloat128
 CFLAGS-tst-strfrom.c += -mfloat128
 CFLAGS-tst-strfrom-locale.c += -mfloat128
 CFLAGS-strfrom-skeleton.c += -mfloat128
+$(foreach test,bug-strtod bug-strtod2 bug-strtod2 tst-strtod-round \
+tst-wcstod-round tst-strtod6 tst-strrom tst-strfrom-locale \
+strfrom-skeleton,$(objpfx)$(test)): gnulib-tests += $(f128-loader-link)
 
 # When building glibc with support for _Float128, the powers of ten tables in
 # fpioconst.c and in the string conversion functions must be extended.
-- 
2.9.4