From 232e45c1720857fbf1948c4aeba39a3c8cc52335 Mon Sep 17 00:00:00 2001

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

Date: Mon, 1 Feb 2021 11:00:38 -0800

Subject: [PATCH 5/5] sysconf: Add _SC_MINSIGSTKSZ/_SC_SIGSTKSZ [BZ #20305]

Add _SC_MINSIGSTKSZ for the minimum signal stack size derived from

AT_MINSIGSTKSZ, which is the minimum number of bytes of free stack

space required in order to gurantee successful, non-nested handling

of a single signal whose handler is an empty function, and _SC_SIGSTKSZ

which is the suggested minimum number of bytes of stack space required

for a signal stack.

If AT_MINSIGSTKSZ isn't available, sysconf (_SC_MINSIGSTKSZ) returns

MINSIGSTKSZ.  On Linux/x86 with XSAVE, the signal frame used by kernel

is composed of the following areas and laid out as:

 ------------------------------

 | alignment padding          |

 ------------------------------

 | xsave buffer               |

 ------------------------------

 | fsave header (32-bit only) |

 ------------------------------

 | siginfo + ucontext         |

 ------------------------------

Compute AT_MINSIGSTKSZ value as size of xsave buffer + size of fsave

header (32-bit only) + size of siginfo and ucontext + alignment padding.

If _SC_SIGSTKSZ_SOURCE or _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ

are redefined as

/* Default stack size for a signal handler: sysconf (SC_SIGSTKSZ).  */

 # undef SIGSTKSZ

 # define SIGSTKSZ sysconf (_SC_SIGSTKSZ)

/* Minimum stack size for a signal handler: SIGSTKSZ.  */

 # undef MINSIGSTKSZ

 # define MINSIGSTKSZ SIGSTKSZ

Compilation will fail if the source assumes constant MINSIGSTKSZ or

SIGSTKSZ.

The reason for not simply increasing the kernel's MINSIGSTKSZ #define

(apart from the fact that it is rarely used, due to glibc's shadowing

definitions) was that userspace binaries will have baked in the old

value of the constant and may be making assumptions about it.

For example, the type (char [MINSIGSTKSZ]) changes if this #define

changes.  This could be a problem if an newly built library tries to

memcpy() or dump such an object defined by and old binary.

Bounds-checking and the stack sizes passed to things like sigaltstack()

and makecontext() could similarly go wrong.

UPDATE:

Backported to glibc 2.28

Signed-off-by: Jair Gonzalez <jair.de.jesus.gonzalez.plascencia@intel.com>

---

 NEWS                                          |  5 ++

 bits/confname.h                               |  8 +-

 bits/sigstksz.h                               | 21 +++++

 elf/dl-support.c                              |  5 ++

 elf/dl-sysdep.c                               |  9 ++

 include/bits/sigstack.h                       |  5 ++

 include/bits/sigstksz.h                       |  7 ++

 include/features.h                            | 11 +++

 manual/conf.texi                              | 21 +++++

 manual/creature.texi                          |  6 ++

 posix/sysconf.c                               |  3 +

 signal/Makefile                               |  5 +-

 signal/signal.h                               |  1 +

 signal/tst-minsigstksz-5.c                    | 84 +++++++++++++++++++

 sysdeps/generic/ldsodefs.h                    |  3 +

 sysdeps/unix/sysv/linux/bits/sigstksz.h       | 33 ++++++++

 .../unix/sysv/linux/ia64/sysconf-sigstksz.h   | 27 ++++++

 sysdeps/unix/sysv/linux/sysconf-sigstksz.h    | 38 +++++++++

 sysdeps/unix/sysv/linux/sysconf.c             |  9 ++

 .../unix/sysv/linux/x86/dl-minsigstacksize.h  | 83 ++++++++++++++++++

 .../sysv/linux/x86/include/bits/sigstack.h    |  5 ++

 sysdeps/x86/dl-minsigstacksize.h              | 27 ++++++

 22 files changed, 413 insertions(+), 3 deletions(-)

 create mode 100644 bits/sigstksz.h

 create mode 100644 include/bits/sigstack.h

 create mode 100644 include/bits/sigstksz.h

 create mode 100644 signal/tst-minsigstksz-5.c

 create mode 100644 sysdeps/unix/sysv/linux/bits/sigstksz.h

 create mode 100644 sysdeps/unix/sysv/linux/ia64/sysconf-sigstksz.h

 create mode 100644 sysdeps/unix/sysv/linux/sysconf-sigstksz.h

 create mode 100644 sysdeps/unix/sysv/linux/x86/dl-minsigstacksize.h

 create mode 100644 sysdeps/unix/sysv/linux/x86/include/bits/sigstack.h

 create mode 100644 sysdeps/x86/dl-minsigstacksize.h

diff --git a/NEWS b/NEWS

index 154ab22d..e0e95cb8 100644

--- a/NEWS

+++ b/NEWS

@@ -9,6 +9,11 @@ Version 2.28

 Major new features:

+* Add _SC_MINSIGSTKSZ and _SC_SIGSTKSZ.  When _SC_SIGSTKSZ_SOURCE or

+  _GNU_SOURCE are defined, MINSIGSTKSZ and SIGSTKSZ are no longer

+  constant on Linux.  MINSIGSTKSZ is redefined to sysconf(_SC_MINSIGSTKSZ)

+  and SIGSTKSZ is redefined to sysconf (_SC_SIGSTKSZ).

+

 * The localization data for ISO 14651 is updated to match the 2016

   Edition 4 release of the standard, this matches data provided by

   Unicode 9.0.0.  This update introduces significant improvements to the

diff --git a/bits/confname.h b/bits/confname.h

index 59d31721..36279222 100644

--- a/bits/confname.h

+++ b/bits/confname.h

@@ -525,8 +525,14 @@ enum

     _SC_THREAD_ROBUST_PRIO_INHERIT,

 #define _SC_THREAD_ROBUST_PRIO_INHERIT	_SC_THREAD_ROBUST_PRIO_INHERIT

-    _SC_THREAD_ROBUST_PRIO_PROTECT

+    _SC_THREAD_ROBUST_PRIO_PROTECT,

 #define _SC_THREAD_ROBUST_PRIO_PROTECT	_SC_THREAD_ROBUST_PRIO_PROTECT

+

+    _SC_MINSIGSTKSZ,

+#define	_SC_MINSIGSTKSZ			_SC_MINSIGSTKSZ

+

+    _SC_SIGSTKSZ

+#define	_SC_SIGSTKSZ			_SC_SIGSTKSZ

   };

 /* Values for the NAME argument to `confstr'.  */

diff --git a/bits/sigstksz.h b/bits/sigstksz.h

new file mode 100644

index 00000000..5535d873

--- /dev/null

+++ b/bits/sigstksz.h

@@ -0,0 +1,21 @@

+/* Definition of MINSIGSTKSZ.  Generic version.

+   Copyright (C) 2020 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

+   <https://www.gnu.org/licenses/>.  */

+

+#ifndef _SIGNAL_H

+# error "Never include <bits/sigstksz.h> directly; use <signal.h> instead."

+#endif

diff --git a/elf/dl-support.c b/elf/dl-support.c

index 34be8e5b..056945d7 100644

--- a/elf/dl-support.c

+++ b/elf/dl-support.c

@@ -131,6 +131,8 @@ void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;

 size_t _dl_pagesize = EXEC_PAGESIZE;

+size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;

+

 int _dl_inhibit_cache;

 unsigned int _dl_osversion;

@@ -287,6 +289,9 @@ _dl_aux_init (ElfW(auxv_t) *av)

       case AT_RANDOM:

 	_dl_random = (void *) av->a_un.a_val;

 	break;

+      case AT_MINSIGSTKSZ:

+    _dl_minsigstacksize = av->a_un.a_val;

+    break;

 # ifdef DL_PLATFORM_AUXV

       DL_PLATFORM_AUXV

 # endif

diff --git a/elf/dl-sysdep.c b/elf/dl-sysdep.c

index 93983251..4bcd75b4 100644

--- a/elf/dl-sysdep.c

+++ b/elf/dl-sysdep.c

@@ -116,6 +116,11 @@ _dl_sysdep_start (void **start_argptr,

   user_entry = (ElfW(Addr)) ENTRY_POINT;

   GLRO(dl_platform) = NULL; /* Default to nothing known about the platform.  */

+  /* NB: Default to a constant CONSTANT_MINSIGSTKSZ.  */

+  _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),

+		  "CONSTANT_MINSIGSTKSZ is constant");

+  GLRO(dl_minsigstacksize) = CONSTANT_MINSIGSTKSZ;

+

   for (av = GLRO(dl_auxv); av->a_type != AT_NULL; set_seen (av++))

     switch (av->a_type)

       {

@@ -180,6 +185,9 @@ _dl_sysdep_start (void **start_argptr,

       case AT_RANDOM:

 	_dl_random = (void *) av->a_un.a_val;

 	break;

+      case AT_MINSIGSTKSZ:

+	GLRO(dl_minsigstacksize) = av->a_un.a_val;

+	break;

 #ifdef DL_PLATFORM_AUXV

       DL_PLATFORM_AUXV

 #endif

@@ -317,6 +325,7 @@ _dl_show_auxv (void)

 	  [AT_L2_CACHEGEOMETRY - 2] =	{ "L2_CACHEGEOMETRY:  0x", hex },

 	  [AT_L3_CACHESIZE - 2] =	{ "L3_CACHESIZE:      ", dec },

 	  [AT_L3_CACHEGEOMETRY - 2] =	{ "L3_CACHEGEOMETRY:  0x", hex },

+	  [AT_MINSIGSTKSZ - 2] =	{ "MINSIGSTKSZ        ", dec },

 	};

       unsigned int idx = (unsigned int) (av->a_type - 2);

diff --git a/include/bits/sigstack.h b/include/bits/sigstack.h

new file mode 100644

index 00000000..eea939f5

--- /dev/null

+++ b/include/bits/sigstack.h

@@ -0,0 +1,5 @@

+#include_next <bits/sigstack.h>

+

+#if !defined _ISOMAC && !defined CONSTANT_MINSIGSTKSZ

+# define CONSTANT_MINSIGSTKSZ MINSIGSTKSZ

+#endif

diff --git a/include/bits/sigstksz.h b/include/bits/sigstksz.h

new file mode 100644

index 00000000..2ca891e9

--- /dev/null

+++ b/include/bits/sigstksz.h

@@ -0,0 +1,7 @@

+/* NB: Don't define MINSIGSTKSZ nor SIGSTKSZ to sysconf (SC_SIGSTKSZ) for

+   glibc build.  IS_IN can only be used when _ISOMAC isn't defined.  */

+#ifdef _ISOMAC

+# include_next <bits/sigstksz.h>

+#elif IS_IN (libsupport)

+# include_next <bits/sigstksz.h>

+#endif

diff --git a/include/features.h b/include/features.h

index 5bed0a49..fdc3d11d 100644

--- a/include/features.h

+++ b/include/features.h

@@ -47,6 +47,8 @@

    _LARGEFILE64_SOURCE	Additional functionality from LFS for large files.

    _FILE_OFFSET_BITS=N	Select default filesystem interface.

    _ATFILE_SOURCE	Additional *at interfaces.

+   _SC_SIGSTKSZ_SOURCE	Select correct (but non compile-time constant)

+			MINSIGSTKSZ and SIGSTKSZ.

    _GNU_SOURCE		All of the above, plus GNU extensions.

    _DEFAULT_SOURCE	The default set of features (taking precedence over

 			__STRICT_ANSI__).

@@ -93,6 +95,8 @@

    __USE_FILE_OFFSET64	Define 64bit interface as default.

    __USE_MISC		Define things from 4.3BSD or System V Unix.

    __USE_ATFILE		Define *at interfaces and AT_* constants for them.

+   __USE_SC_SIGSTKSZ	Define correct (but non compile-time constant)

+			MINSIGSTKSZ and SIGSTKSZ.

    __USE_GNU		Define GNU extensions.

    __USE_FORTIFY_LEVEL	Additional security measures used, according to level.

@@ -136,6 +140,7 @@

 #undef	__USE_FILE_OFFSET64

 #undef	__USE_MISC

 #undef	__USE_ATFILE

+#undef	__USE_SC_SIGSTKSZ

 #undef	__USE_GNU

 #undef	__USE_FORTIFY_LEVEL

 #undef	__KERNEL_STRICT_NAMES

@@ -208,6 +213,8 @@

 # define _DEFAULT_SOURCE	1

 # undef  _ATFILE_SOURCE

 # define _ATFILE_SOURCE	1

+# undef  _SC_SIGSTKSZ_SOURCE

+# define _SC_SIGSTKSZ_SOURCE 1

 #endif

 /* If nothing (other than _GNU_SOURCE and _DEFAULT_SOURCE) is defined,

@@ -372,6 +379,10 @@

 # define __USE_ATFILE	1

 #endif

+#ifdef	_SC_SIGSTKSZ_SOURCE

+# define __USE_SC_SIGSTKSZ	1

+#endif

+

 #ifdef	_GNU_SOURCE

 # define __USE_GNU	1

 #endif

diff --git a/manual/conf.texi b/manual/conf.texi

index dbd1d302..7321f401 100644

--- a/manual/conf.texi

+++ b/manual/conf.texi

@@ -911,6 +911,27 @@ Inquire about the parameter corresponding to @code{NL_SETMAX}.

 @item _SC_NL_TEXTMAX

 @standards{X/Open, unistd.h}

 Inquire about the parameter corresponding to @code{NL_TEXTMAX}.

+

+@item _SC_MINSIGSTKSZ

+@standards{GNU, unistd.h}

+Inquire about the minimum number of bytes of free stack space required

+in order to guarantee successful, non-nested handling of a single signal

+whose handler is an empty function.

+

+@item _SC_SIGSTKSZ

+@standards{GNU, unistd.h}

+Inquire about the suggested minimum number of bytes of stack space

+required for a signal stack.

+

+This is not guaranteed to be enough for any specific purpose other than

+the invocation of a single, non-nested, empty handler, but nonetheless

+should be enough for basic scenarios involving simple signal handlers

+and very low levels of signal nesting (say, 2 or 3 levels at the very

+most).

+

+This value is provided for developer convenience and to ease migration

+from the legacy @code{SIGSTKSZ} constant.  Programs requiring stronger

+guarantees should avoid using it if at all possible.

 @end vtable

 @node Examples of Sysconf

--- a/manual/creature.texi   2022-04-14 11:40:12.081653162 +0300

+++ b/manual/creature.texi       2022-04-14 11:41:54.376167038 +0300

@@ -251,6 +251,12 @@

 checks that may have an additional performance overhead.

 @end defvr

+@defvr Macro _SC_SIGSTKSZ_SOURCE

+@standards{GNU, (none)}

+If this macro is defined, correct (but non compile-time constant)

+MINSIGSTKSZ and SIGSTKSZ are defined.

+@end defvr

+

 @defvr Macro _REENTRANT

 @defvrx Macro _THREAD_SAFE

 @standards{Obsolete, (none)}

diff --git a/posix/sysconf.c b/posix/sysconf.c

index 09ebd95a..48c925f5 100644

--- a/posix/sysconf.c

+++ b/posix/sysconf.c

@@ -266,6 +266,9 @@ __sysconf (int name)

     case _SC_XOPEN_REALTIME:

     case _SC_XOPEN_REALTIME_THREADS:

+    case _SC_MINSIGSTKSZ:

+    case _SC_SIGSTKSZ:

+

       break;

     }

diff --git a/signal/Makefile b/signal/Makefile

index 7767bb28..cd85b8b6 100644

--- a/signal/Makefile

+++ b/signal/Makefile

@@ -31,7 +31,8 @@ headers := signal.h sys/signal.h \

 	   bits/types/sigevent_t.h bits/types/siginfo_t.h \

 	   bits/types/sigset_t.h bits/types/sigval_t.h \

 	   bits/types/stack_t.h bits/types/struct_sigstack.h \

-	   bits/types/__sigval_t.h

+	   bits/types/__sigval_t.h \

+	   bits/sigstksz.h

 routines	:= signal raise killpg \

 		   sigaction sigprocmask kill \

@@ -48,7 +49,7 @@ routines	:= signal raise killpg \

 tests		:= tst-signal tst-sigset tst-sigsimple tst-raise tst-sigset2 \

 		   tst-sigwait-eintr tst-sigaction \

 		   tst-minsigstksz-1 tst-minsigstksz-2 tst-minsigstksz-3 \

-		   tst-minsigstksz-3a tst-minsigstksz-4 \

+		   tst-minsigstksz-3a tst-minsigstksz-4 tst-minsigstksz-5

 include ../Rules

diff --git a/signal/signal.h b/signal/signal.h

index 87dc82a9..8ebfc6e6 100644

--- a/signal/signal.h

+++ b/signal/signal.h

@@ -314,6 +314,7 @@ extern int sigreturn (struct sigcontext *__scp) __THROW;

 extern int siginterrupt (int __sig, int __interrupt) __THROW;

 # include <bits/sigstack.h>

+# include <bits/sigstksz.h>

 # include <bits/ss_flags.h>

 /* Alternate signal handler stack interface.

diff --git a/signal/tst-minsigstksz-5.c b/signal/tst-minsigstksz-5.c

new file mode 100644

index 00000000..d657d2f4

--- /dev/null

+++ b/signal/tst-minsigstksz-5.c

@@ -0,0 +1,84 @@

+/* Test of signal delivery on an alternate stack with MINSIGSTKSZ size.

+   Copyright (C) 2020 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

+   <https://www.gnu.org/licenses/>.  */

+

+#include <signal.h>

+#include <stdlib.h>

+#include <string.h>

+#include <unistd.h>

+#include <support/check.h>

+#include <support/support.h>

+

+static volatile sig_atomic_t handler_run;

+

+static void

+handler (int signo)

+{

+  /* Clear a bit of on-stack memory.  */

+  volatile char buffer[256];

+  for (size_t i = 0; i < sizeof (buffer); ++i)

+    buffer[i] = 0;

+  handler_run = 1;

+}

+

+int

+do_test (void)

+{

+  size_t stack_buffer_size = 64 * 1024 * 1024;

+  void *stack_buffer = xmalloc (stack_buffer_size);

+  void *stack_end = stack_buffer + stack_buffer_size;

+  memset (stack_buffer, 0xCC, stack_buffer_size);

+

+  void *stack_bottom = stack_buffer + (stack_buffer_size + MINSIGSTKSZ) / 2;

+  void *stack_top = stack_bottom + MINSIGSTKSZ;

+  stack_t stack =

+    {

+      .ss_sp = stack_bottom,

+      .ss_size = MINSIGSTKSZ,

+    };

+  if (sigaltstack (&stack, NULL) < 0)

+    FAIL_RET ("sigaltstack: %m\n");

+

+  struct sigaction act =

+    {

+      .sa_handler = handler,

+      .sa_flags = SA_ONSTACK,

+    };

+  if (sigaction (SIGUSR1, &act, NULL) < 0)

+    FAIL_RET ("sigaction: %m\n");

+

+  if (kill (getpid (), SIGUSR1) < 0)

+    FAIL_RET ("kill: %m\n");

+

+  if (handler_run != 1)

+    FAIL_RET ("handler did not run\n");

+

+  for (void *p = stack_buffer; p < stack_bottom; ++p)

+    if (*(unsigned char *) p != 0xCC)

+      FAIL_RET ("changed byte %ld bytes below configured stack\n",

+		(long) (stack_bottom - p));

+  for (void *p = stack_top; p < stack_end; ++p)

+    if (*(unsigned char *) p != 0xCC)

+      FAIL_RET ("changed byte %ld bytes above configured stack\n",

+		(long) (p - stack_top));

+

+  free (stack_buffer);

+

+  return 0;

+}

+

+#include <support/test-driver.c>

diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h

index 6cbbaa80..a15bf2e5 100644

--- a/sysdeps/generic/ldsodefs.h

+++ b/sysdeps/generic/ldsodefs.h

@@ -527,6 +527,9 @@ struct rtld_global_ro

   /* Cached value of `getpagesize ()'.  */

   EXTERN size_t _dl_pagesize;

+  /* Cached value of `sysconf (_SC_MINSIGSTKSZ)'.  */

+  EXTERN size_t _dl_minsigstacksize;

+

   /* Do we read from ld.so.cache?  */

   EXTERN int _dl_inhibit_cache;

diff --git a/sysdeps/unix/sysv/linux/bits/sigstksz.h b/sysdeps/unix/sysv/linux/bits/sigstksz.h

new file mode 100644

index 00000000..926508f2

--- /dev/null

+++ b/sysdeps/unix/sysv/linux/bits/sigstksz.h

@@ -0,0 +1,33 @@

+/* Definition of MINSIGSTKSZ and SIGSTKSZ.  Linux version.

+   Copyright (C) 2020 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

+   <https://www.gnu.org/licenses/>.  */

+

+#ifndef _SIGNAL_H

+# error "Never include <bits/sigstksz.h> directly; use <signal.h> instead."

+#endif

+

+#if defined __USE_SC_SIGSTKSZ && __USE_SC_SIGSTKSZ

+# include <unistd.h>

+

+/* Default stack size for a signal handler: sysconf (SC_SIGSTKSZ).  */

+# undef SIGSTKSZ

+# define SIGSTKSZ sysconf (_SC_SIGSTKSZ)

+

+/* Minimum stack size for a signal handler: SIGSTKSZ.  */

+# undef MINSIGSTKSZ

+# define MINSIGSTKSZ SIGSTKSZ

+#endif

diff --git a/sysdeps/unix/sysv/linux/ia64/sysconf-sigstksz.h b/sysdeps/unix/sysv/linux/ia64/sysconf-sigstksz.h

new file mode 100644

index 00000000..7e5ceba1

--- /dev/null

+++ b/sysdeps/unix/sysv/linux/ia64/sysconf-sigstksz.h

@@ -0,0 +1,27 @@

+/* sysconf_sigstksz ().  Linux/ia64 version.

+   Copyright (C) 2020 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

+   <https://www.gnu.org/licenses/>.  */

+

+/* Return sysconf (_SC_SIGSTKSZ).  */

+

+static long int

+sysconf_sigstksz (void)

+{

+  _Static_assert (__builtin_constant_p (SIGSTKSZ),

+		  "SIGSTKSZ is constant");

+  return SIGSTKSZ;

+}

diff --git a/sysdeps/unix/sysv/linux/sysconf-sigstksz.h b/sysdeps/unix/sysv/linux/sysconf-sigstksz.h

new file mode 100644

index 00000000..64d450b2

--- /dev/null

+++ b/sysdeps/unix/sysv/linux/sysconf-sigstksz.h

@@ -0,0 +1,38 @@

+/* sysconf_sigstksz ().  Linux version.

+   Copyright (C) 2020 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

+   <https://www.gnu.org/licenses/>.  */

+

+/* Return sysconf (_SC_SIGSTKSZ).  */

+

+static long int

+sysconf_sigstksz (void)

+{

+  long int minsigstacksize = GLRO(dl_minsigstacksize);

+  assert (minsigstacksize != 0);

+  _Static_assert (__builtin_constant_p (MINSIGSTKSZ),

+		  "MINSIGSTKSZ is constant");

+  if (minsigstacksize < MINSIGSTKSZ)

+    minsigstacksize = MINSIGSTKSZ;

+  /* MAX (MINSIGSTKSZ, sysconf (_SC_MINSIGSTKSZ)) * 4.  */

+  long int sigstacksize = minsigstacksize * 4;

+  /* Return MAX (SIGSTKSZ, sigstacksize).  */

+  _Static_assert (__builtin_constant_p (SIGSTKSZ),

+		  "SIGSTKSZ is constant");

+  if (sigstacksize < SIGSTKSZ)

+    sigstacksize = SIGSTKSZ;

+  return sigstacksize;

+}

diff --git a/sysdeps/unix/sysv/linux/sysconf.c b/sysdeps/unix/sysv/linux/sysconf.c

index 6fab1601..4aa9b171 100644

--- a/sysdeps/unix/sysv/linux/sysconf.c

+++ b/sysdeps/unix/sysv/linux/sysconf.c

@@ -16,6 +16,7 @@

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

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

+#include <assert.h>

 #include <errno.h>

 #include <fcntl.h>

 #include <stdlib.h>

@@ -26,6 +27,7 @@

 #include <sys/param.h>

 #include <not-cancel.h>

 #include <ldsodefs.h>

+#include <sysconf-sigstksz.h>

 /* Legacy value of ARG_MAX.  The macro is now not defined since the

    actual value varies based on the stack size.  */

@@ -75,6 +77,13 @@ __sysconf (int name)

       }

       break;

+    case _SC_MINSIGSTKSZ:

+      assert (GLRO(dl_minsigstacksize) != 0);

+      return GLRO(dl_minsigstacksize);

+

+    case _SC_SIGSTKSZ:

+      return sysconf_sigstksz ();

+

     default:

       break;

     }

diff --git a/sysdeps/unix/sysv/linux/x86/dl-minsigstacksize.h b/sysdeps/unix/sysv/linux/x86/dl-minsigstacksize.h

new file mode 100644

index 00000000..6088bbc9

--- /dev/null

+++ b/sysdeps/unix/sysv/linux/x86/dl-minsigstacksize.h

@@ -0,0 +1,83 @@

+/* Emulate AT_MINSIGSTKSZ.  Linux/x86 version.

+   Copyright (C) 2020 Free Software Foundation, Inc.

+

+   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

+   <https://www.gnu.org/licenses/>.  */

+

+/* Emulate AT_MINSIGSTKSZ with XSAVE. */

+

+static inline void

+dl_check_minsigstacksize (const struct cpu_features *cpu_features)

+{

+  /* Return if AT_MINSIGSTKSZ is provide by kernel.  */

+  if (GLRO(dl_minsigstacksize) != 0)

+    return;

+

+  if (cpu_features->basic.max_cpuid >= 0xd

+      && CPU_FEATURES_CPU_P (cpu_features, OSXSAVE))

+    {

+      /* Emulate AT_MINSIGSTKSZ.  In Linux kernel, the signal frame data

+	 with XSAVE is composed of the following areas and laid out as:

+	 ------------------------------

+	 | alignment padding          |

+	 ------------------------------

+	 | xsave buffer               |

+	 ------------------------------

+	 | fsave header (32-bit only) |

+	 ------------------------------

+	 | siginfo + ucontext         |

+	 ------------------------------

+	 */

+

+      unsigned int sigframe_size;

+

+#ifdef __x86_64__

+      /* NB: sizeof(struct rt_sigframe) + 8-byte return address in Linux

+	 kernel.  */

+      sigframe_size = 440 + 8;

+#else

+      /* NB: sizeof(struct sigframe_ia32) + sizeof(struct fregs_state)) +

+	 4-byte return address + 3 * 4-byte arguments in Linux kernel.  */

+      sigframe_size = 736 + 112 + 4 + 3 * 4;

+#endif

+

+      /* Add 15 bytes to align the stack to 16 bytes.  */

+      sigframe_size += 15;

+

+      /* Make the space before xsave buffer multiple of 16 bytes.  */

+      sigframe_size = ALIGN_UP (sigframe_size, 16);

+

+      /* Add (64 - 16)-byte padding to align xsave buffer at 64 bytes.  */

+      sigframe_size += 64 - 16;

+

+      unsigned int eax, ebx, ecx, edx;

+      __cpuid_count (0xd, 0, eax, ebx, ecx, edx);

+

+      /* Add the size of xsave buffer.  */

+      sigframe_size += ebx;

+

+      /* Add the size of FP_XSTATE_MAGIC2.  */

+#define FP_XSTATE_MAGIC2 0x46505845U

+      sigframe_size += sizeof (FP_XSTATE_MAGIC2);

+

+      GLRO(dl_minsigstacksize) = sigframe_size;

+    }