Backport of this upstream patch:

commit 031e519c95c069abe4e4c7c59e2b4b67efccdee5

Author: H.J. Lu <hjl.tools@gmail.com>

Date:   Thu Jul 6 04:43:06 2017 -0700

    x86-64: Align the stack in __tls_get_addr [BZ #21609]

    This change forces realignment of the stack pointer in __tls_get_addr, so

    that binaries compiled by GCCs older than GCC 4.9:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58066

    continue to work even if vector instructions are used in glibc which

    require the ABI stack realignment.

    __tls_get_addr_slow is added to handle the slow paths in the default

    implementation of__tls_get_addr in elf/dl-tls.c.  The new __tls_get_addr

    calls __tls_get_addr_slow after realigning the stack.  Internal calls

    within ld.so go directly to the default implementation of __tls_get_addr

    because they do not need stack realignment.

            [BZ #21609]

            * sysdeps/x86_64/Makefile (sysdep-dl-routines): Add tls_get_addr.

            (gen-as-const-headers): Add rtld-offsets.sym.

            * sysdeps/x86_64/dl-tls.c: New file.

            * sysdeps/x86_64/rtld-offsets.sym: Likwise.

            * sysdeps/x86_64/tls_get_addr.S: Likewise.

            * sysdeps/x86_64/dl-tls.h: Add multiple inclusion guards.

            * sysdeps/x86_64/tlsdesc.sym (TI_MODULE_OFFSET): New.

            (TI_OFFSET_OFFSET): Likwise.

Adjusted for drift in sysdeps/x86_64/Makefile and lack of

TLS_DTV_UNALLOCATED consolidation (upstream commit

aca1daef298b43bd7b1987b31f5aabcf6c2f6021).

diff --git a/sysdeps/x86_64/Makefile b/sysdeps/x86_64/Makefile

index 6c03a89fb3ea3063..c6766bb2b443a28a 100644

--- a/sysdeps/x86_64/Makefile

+++ b/sysdeps/x86_64/Makefile

@@ -19,7 +19,7 @@ gen-as-const-headers += locale-defines.sym

 endif

 ifeq ($(subdir),elf)

-sysdep-dl-routines += tlsdesc dl-tlsdesc

+sysdep-dl-routines += tlsdesc dl-tlsdesc tls_get_addr

 tests += ifuncmain8

 modules-names += ifuncmod8

@@ -69,5 +69,5 @@ endif

 endif

 ifeq ($(subdir),csu)

-gen-as-const-headers += tlsdesc.sym

+gen-as-const-headers += tlsdesc.sym rtld-offsets.sym

 endif

diff --git a/sysdeps/x86_64/dl-tls.c b/sysdeps/x86_64/dl-tls.c

new file mode 100644

index 0000000000000000..3584805c8ecca59a

--- /dev/null

+++ b/sysdeps/x86_64/dl-tls.c

@@ -0,0 +1,53 @@

+/* Thread-local storage handling in the ELF dynamic linker.  x86-64 version.

+   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/>.  */

+

+#ifdef SHARED

+/* Work around GCC PR58066, due to which __tls_get_addr may be called

+   with an unaligned stack.  The compat implementation is in

+   tls_get_addr-compat.S.  */

+

+# include <dl-tls.h>

+

+/* Define __tls_get_addr within elf/dl-tls.c under a different

+   name.  */

+extern __typeof__ (__tls_get_addr) ___tls_get_addr;

+

+# define __tls_get_addr ___tls_get_addr

+# include <elf/dl-tls.c>

+# undef __tls_get_addr

+

+hidden_ver (___tls_get_addr, __tls_get_addr)

+

+/* Only handle slow paths for __tls_get_addr.  */

+attribute_hidden

+void *

+__tls_get_addr_slow (GET_ADDR_ARGS)

+{

+  dtv_t *dtv = THREAD_DTV ();

+

+  if (__glibc_unlikely (dtv[0].counter != GL(dl_tls_generation)))

+    return update_get_addr (GET_ADDR_PARAM);

+

+  return tls_get_addr_tail (GET_ADDR_PARAM, dtv, NULL);

+}

+#else

+

+/* No compatibility symbol needed.  */

+# include <elf/dl-tls.c>

+

+#endif

diff --git a/sysdeps/x86_64/dl-tls.h b/sysdeps/x86_64/dl-tls.h

index 56162ee64a4aae7d..0b4a6b3b634a83f4 100644

--- a/sysdeps/x86_64/dl-tls.h

+++ b/sysdeps/x86_64/dl-tls.h

@@ -16,6 +16,10 @@

    License along with the GNU C Library; if not, see

    <http://www.gnu.org/licenses/>.  */

+#ifndef _X86_64_DL_TLS_H

+#define _X86_64_DL_TLS_H

+

+#include <stdint.h>

 /* Type used for the representation of TLS information in the GOT.  */

 typedef struct dl_tls_index

@@ -29,3 +33,5 @@ extern void *__tls_get_addr (tls_index *ti);

 /* Value used for dtv entries for which the allocation is delayed.  */

 #define TLS_DTV_UNALLOCATED	((void *) -1l)

+

+#endif /* _X86_64_DL_TLS_H */

diff --git a/sysdeps/x86_64/rtld-offsets.sym b/sysdeps/x86_64/rtld-offsets.sym

new file mode 100644

index 0000000000000000..fd41b51521ac80bd

--- /dev/null

+++ b/sysdeps/x86_64/rtld-offsets.sym

@@ -0,0 +1,6 @@

+#define SHARED

+#include <ldsodefs.h>

+

+--

+

+GL_TLS_GENERATION_OFFSET        offsetof (struct rtld_global, _dl_tls_generation)

diff --git a/sysdeps/x86_64/tls_get_addr.S b/sysdeps/x86_64/tls_get_addr.S

new file mode 100644

index 0000000000000000..9d38fb3be54fbcb5

--- /dev/null

+++ b/sysdeps/x86_64/tls_get_addr.S

@@ -0,0 +1,61 @@

+/* Stack-aligning implementation of __tls_get_addr.  x86-64 version.

+   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/>.  */

+

+#ifdef SHARED

+

+# include <sysdep.h>

+# include "tlsdesc.h"

+# include "rtld-offsets.h"

+

+/* See __tls_get_addr and __tls_get_addr_slow in dl-tls.c.  This function

+   call __tls_get_addr_slow on both slow paths.  It realigns the stack

+   before the call to work around GCC PR58066.  */

+

+ENTRY (__tls_get_addr)

+	mov 	%fs:DTV_OFFSET, %RDX_LP

+	mov	GL_TLS_GENERATION_OFFSET+_rtld_local(%rip), %RAX_LP

+	/* GL(dl_tls_generation) == dtv[0].counter */

+	cmp	%RAX_LP, (%rdx)

+	jne	1f

+	mov	TI_MODULE_OFFSET(%rdi), %RAX_LP

+	/* dtv[ti->ti_module] */

+# ifdef __LP64__

+	salq	$4, %rax

+	movq	(%rdx,%rax), %rax

+# else

+	movl	(%rdx,%rax, 8), %eax

+# endif

+	cmp	$-1, %RAX_LP

+	je	1f

+	add	TI_OFFSET_OFFSET(%rdi), %RAX_LP

+	ret

+1:

+	/* On the slow path, align the stack.  */

+	pushq	%rbp

+	cfi_def_cfa_offset (16)

+	cfi_offset (%rbp, -16)

+	mov	%RSP_LP, %RBP_LP

+	cfi_def_cfa_register (%rbp)

+	and	$-16, %RSP_LP

+	call	__tls_get_addr_slow

+	mov	%RBP_LP, %RSP_LP

+	popq	%rbp

+	cfi_def_cfa (%rsp, 8)

+	ret

+END (__tls_get_addr)

+#endif /* SHARED */

diff --git a/sysdeps/x86_64/tlsdesc.sym b/sysdeps/x86_64/tlsdesc.sym

index 33854975d04184b2..fc897ab4b522b1a9 100644

--- a/sysdeps/x86_64/tlsdesc.sym

+++ b/sysdeps/x86_64/tlsdesc.sym

@@ -15,3 +15,6 @@ TLSDESC_ARG			offsetof(struct tlsdesc, arg)

 TLSDESC_GEN_COUNT		offsetof(struct tlsdesc_dynamic_arg, gen_count)

 TLSDESC_MODID			offsetof(struct tlsdesc_dynamic_arg, tlsinfo.ti_module)

 TLSDESC_MODOFF			offsetof(struct tlsdesc_dynamic_arg, tlsinfo.ti_offset)

+

+TI_MODULE_OFFSET 		offsetof(tls_index, ti_module)

+TI_OFFSET_OFFSET 		offsetof(tls_index, ti_offset)