hurd: Fix early rtld access to errno
Commit Message
* 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
Comments
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
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
@@ -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>
@@ -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
new file mode 100644
@@ -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