hurd: Fix early rtld access to errno

Message ID 20180318015332.9759-1-samuel.thibault@ens-lyon.org
State New
Headers show
Series
  • hurd: Fix early rtld access to errno
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Commit Message

Samuel Thibault March 18, 2018, 1:53 a.m.
* sysdeps/generic/dl-sysdep.h (RTLD_EXTERN_ERRNO): Define macro to 0.
	* sysdeps/mach/hurd/i386/dl-sysdep.h: Include <dl-sysdep.h>.
	[IS_IN(rtld)] (RTLD_EXTERN_ERRNO): Define macro to 1.
	[!IS_IN(rtld)] (RTLD_EXTERN_ERRNO): Define macro to 0.
	* include/errno.h [IS_IN(rtld) && !defined RTLD_EXTERN_ERRNO]: Error
	out.
	[!IS_IN(rtld)] (RTLD_EXTERN_ERRNO): Define to 0.
	[RTLD_EXTERN_ERRNO]: Do not use TLS access to errno.
---
 include/errno.h                    |  6 +++++-
 sysdeps/generic/dl-sysdep.h        |  8 ++++++++
 sysdeps/mach/hurd/i386/dl-sysdep.h | 27 +++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/mach/hurd/i386/dl-sysdep.h

-- 
2.16.2

Comments

Samuel Thibault March 18, 2018, 2:07 a.m. | #1
Samuel Thibault, on dim. 18 mars 2018 02:53:32 +0100, wrote:
> 	* sysdeps/generic/dl-sysdep.h (RTLD_EXTERN_ERRNO): Define macro to 0.

> 	* sysdeps/mach/hurd/i386/dl-sysdep.h: Include <dl-sysdep.h>.

> 	[IS_IN(rtld)] (RTLD_EXTERN_ERRNO): Define macro to 1.

> 	[!IS_IN(rtld)] (RTLD_EXTERN_ERRNO): Define macro to 0.

> 	* include/errno.h [IS_IN(rtld) && !defined RTLD_EXTERN_ERRNO]: Error

> 	out.

> 	[!IS_IN(rtld)] (RTLD_EXTERN_ERRNO): Define to 0.

> 	[RTLD_EXTERN_ERRNO]: Do not use TLS access to errno.


All that being said, I'm surprised: AIUI this problem would be the
same on all platforms as soon as one would set RTLD_PRIVATE_ERRNO to
0.

Trying to set RTLD_PRIVATE_ERRNO to 0 on Linux x86_64 for instance,
ld.so crashes in

assert (info[DT_FLAGS] == NULL
	  || (info[DT_FLAGS]->d_un.d_val & ~DF_BIND_NOW) == 0);

since __thread access produces DF_STATIC_TLS. Ignoring that check just
pushes the crash to open_verify()'s __set_errno call, on fs:(%eax) or
fs:0 access (depending whether initial-exec TLS model is enabled or
not).  I guess that at that point Linux x86_64 hasn't initialized %fs
yet.  I tried to just disable the use of __thread access to errno in
rtld with

> @@ -20,7 +24,7 @@

>  #  define errno rtld_errno

>  extern int rtld_errno attribute_hidden;

>  

> -# elif IS_IN_LIB

> +# elif IS_IN_LIB && !IS_IN(rtld)

>  

>  #  include <tls.h>

>  


But that's only pushing the issue to the __errno_location()
function. In sysdeps/mach/hurd/errno-loc.c I made the rtld version of
__errno_location() a weak function which avoids accessing TLS by using
a static variable, that function being overriden by libc as soon as it
gets loaded.  I'm actually wondering why not all archs would need this
when RTLD_PRIVATE_ERRNO is 0.

Samuel
Florian Weimer March 19, 2018, 9:22 a.m. | #2
On 03/18/2018 03:07 AM, Samuel Thibault wrote:
> All that being said, I'm surprised: AIUI this problem would be the

> same on all platforms as soon as one would set RTLD_PRIVATE_ERRNO to

> 0.


I think this is presently a knob for Hurd only.  It might have been 
different in the LinuxThreads days, though.

Thanks,
Florian

Patch

diff --git a/include/errno.h b/include/errno.h
index 3c3d2288c8..792f974518 100644
--- a/include/errno.h
+++ b/include/errno.h
@@ -7,8 +7,12 @@ 
 #  ifndef RTLD_PRIVATE_ERRNO
 #   error "dl-sysdep.h must define RTLD_PRIVATE_ERRNO!"
 #  endif
+#  ifndef RTLD_EXTERN_ERRNO
+#   error "dl-sysdep.h must define RTLD_EXTERN_ERRNO!"
+#  endif
 # else
 #  define RTLD_PRIVATE_ERRNO	0
+#  define RTLD_EXTERN_ERRNO	0
 # endif
 
 # if RTLD_PRIVATE_ERRNO
@@ -20,7 +24,7 @@ 
 #  define errno rtld_errno
 extern int rtld_errno attribute_hidden;
 
-# elif IS_IN_LIB
+# elif IS_IN_LIB && !RTLD_EXTERN_ERRNO
 
 #  include <tls.h>
 
diff --git a/sysdeps/generic/dl-sysdep.h b/sysdeps/generic/dl-sysdep.h
index 2cb8565b5b..d787f142e9 100644
--- a/sysdeps/generic/dl-sysdep.h
+++ b/sysdeps/generic/dl-sysdep.h
@@ -32,3 +32,11 @@ 
 #else
 # define RTLD_PRIVATE_ERRNO 0
 #endif
+
+/* This macro must be defined to either 0 or 1.
+
+   If 1, then ld.so will use the external errno access through
+   __errno_location().  This may be needed if early TLS access to
+   errno can not work. */
+
+#define RTLD_EXTERN_ERRNO 0
diff --git a/sysdeps/mach/hurd/i386/dl-sysdep.h b/sysdeps/mach/hurd/i386/dl-sysdep.h
new file mode 100644
index 0000000000..1533753a49
--- /dev/null
+++ b/sysdeps/mach/hurd/i386/dl-sysdep.h
@@ -0,0 +1,27 @@ 
+/* System-specific settings for dynamic linker code.  Hurd version.
+   Copyright (C) 2002-2018 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_next <dl-sysdep.h>
+
+/* TLS access can not work early in ld.so.  */
+
+#if IS_IN (rtld)
+# define RTLD_EXTERN_ERRNO 1
+#else
+# define RTLD_EXTERN_ERRNO 0
+#endif