| Age | Commit message (Collapse) | Author |
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Patch "LT.old: Make __errno_location/__h_errno_location thread safe"
uncovered yet another bug with static linking and errno (hopefully this
is last of them all).
Currently, __errno_location is declared weak but is defined strong.
While this provides with the desired weak semantics in dso, it
is subtly broken in static links.
Quoting Joern Rennecke (ARC gcc expert):
| I think the issue is that you declare the function as weak in the
| header file. That is a rare instance where you want the reference
| use declaration that differs a bit from the definition.
| If the reference uses a weakly declared function, that creates a
| weakref, i.e. the linker won't bother to look for this symbol at
| all - if it gets linked in for some other reason, fine,
| otherwise, it stays zero.
So the solution to declare strong, define weak.
Supporting data
-----------------
orig code: ARM mmap wrapper (LT.old build + my prev patch for errno)
_mmap:
@ args = 8, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
stmfd sp!, {r4, r5, r7, lr}
ldr r5, [sp, #20]
movs ip, r5, asl #20
beq .L2
bl __errno_location(PLT)
mov r3, #22
str r3, [r0, #0]
mvn r0, #0
...
...
.weak __errno_location
A statically linked hello world program which uses mmap too.
As we can see__errno_location is completely gone - which is
semantically wrong - we need functional errno.
00008274 <__GI_mmap>:
8274: e92d40b0 push {r4, r5, r7, lr}
8278: e59d5014 ldr r5, [sp, #20]
827c: e1b0ca05 lsls ip, r5, #20
8280: 0a000004 beq 8298
8284: e320f000 nop {0}
^^^^^^^^^^
8288: e3a03016 mov r3, #22
828c: e5803000 str r3, [r0]
8290: e3e00000 mvn r0, #0
This in turn is due to a fixup in ARM ld which transforms branch-to-null
into a nop. It is better than crashing but still wrong since errno
handling is removed.
With the patch, errno_location is restored back in test program.
00008274 <__GI_mmap>:
8274: e92d40b0 push {r4, r5, r7, lr}
8278: e59d5014 ldr r5, [sp, #20]
827c: e1b0ca05 lsls ip, r5, #20
8280: 0a000004 beq 8298 <__GI_mmap+0x24>
8284: eb000010 bl 82cc <__errno_location>
8288: e3a03016 mov r3, #22
828c: e5803000 str r3, [r0]
Cc: Christian Ruppert <christian.ruppert@abilis.com>
CC: Francois Bedard <Francois.Bedard@synopsys.com>
Cc: Anton Kolesov <Anton.Kolesov@synopsys.com>
Cc: Joern Rennecke <joern.rennecke@embecosm.com>
Cc: Jeremy Bennett <jeremy.bennett@embecosm.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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WHY: errno in uClibc is not thread safe
HOW: __errno_location and it's sibling __h_errno_location need to be called
via PLT - even from within libc. That way when linked with pthread,
intra-uClibc callers will also use the thread safe version.
This is achieved by removing the GI alias for these functions,
ensuring that they get called normally (via PLT)
Verified with ARC LT.old and ARM cubieboard2 buildroot (LT.old)
NPTL is unaffected by this bug.
------------ History behind this patch ---------------------
This is a long standing bug (https://bugs.busybox.net/show_bug.cgi?id=2089)
Others have tried to fix it in past (alteast Peter Korsgaard's patch in 2010),
but somehow failed to be merged (or were backed out afterwards).
http://lists.uclibc.org/pipermail/uclibc/2010-July/044176.html
One of the causes could be side effect of atleast one more bug related to
pthreads and static link which has now been fixed.
http://lists.uclibc.org/pipermail/uclibc/2013-October/047958.html
I have solved this w/o looking at other pacthes but would like to give
credit to Peter and others for confirming that it makes sense.
Cc: Christian Ruppert <christian.ruppert@abilis.com>
CC: Francois Bedard <Francois.Bedard@synopsys.com>
Cc: Joern Rennecke <joern.rennecke@embecosm.com>
Cc: Jeremy Bennett <jeremy.bennett@embecosm.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Khem Raj <raj.khem@gmail.com>
Cc: buildroot@busybox.net
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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A simple statically linked hello world program was segfaulting for ARC
in linuxthreads.old configuration (although the root casue applies
cross-arch for NPTL as well as linuxthreads.old as described)
The crash was due to branch to NULL in _stdio_init
0001026c <_stdio_init>:
1026c: push_s blink
1026e: st.a r13,[sp,-8]
10272: bl.d 0 --> supposed call to __errno_location
The call was NOT getting patched to libc internal only alias
__GI___errno_location, because it was weak while it's exported cousin,
__errno_location was strong/normal.
arc-linux-uclibc-nm libc/misc/internals/__errno_location.os
00000000 W __GI___errno_location
00000000 T __errno_location
This is exactly opposite to what is expected.
Quoting Peter S. Mazinger, commit 87936cd013041 "errno and *_init cleanup"
| The rule adopted:
| for enabled threads we make in libc the __GI_x() variants strong, x() weak
| and (should) provide another strong x() in libpthread.
| If threads are disabled, even the __GI_x() variants are weak.
With the fix, we see the right settings as below
00000000 T __GI___errno_location
00000000 W __errno_location
Note that problem won't show up in a static busybox build as it references
errno and that seems to elide the issue.
I can confirm the same/more issues with latest ARM buildroot builds w/o
my fix.
(1). linuxthreads.old (broken just like ARC)
arm-linux-nm uclibc-snapshot/libc/misc/internals/__errno_location.os
00000000 W __GI___errno_location
00000000 T __errno_location
But presumably the issue there is NOT catestrophic because ARM linker is
likely smarter and patches a NOP instead of NULL branch.
00008388 <_stdio_init>:
8388: e92d4038 push {r3, r4, r5, lr}
838c: e320f000 nop {0}
(2) NPTL build (exported version is not weak)
00000000 T __GI___errno_location
00000000 T __errno_location
This causes a static link with libpthread and test program
referencing errno to fail to link.
#include <errno.h>
int main(void)
{
printf("%d\n", errno);
}
arm-linux-gcc -static -pthread -o tst tst.o
arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libc.a(__errno_location.os):
In function `__errno_location': __errno_location.c:(.text+0x0):
multiple definition of `__errno_location'
arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libpthread.a
(errno_location.os):errno_location.c:(.text+0x0): first defined here
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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Move h_errno related stuff to separate file.
Do not hide errno and h_errno for non-TLS, else it keeps being 0.
Make __[h_]errno_location weak for non-TLS.
Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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Define a common view of __errno_location, __h_errno_location in common header
and use that everywhere, __uClibc_main.c is no special.
The rule adopted:
for enabled threads we make in libc the __GI_x() variants strong, x() weak
and (should) provide another strong x() in libpthread.
If threads are disabled, even the __GI_x() variants are weak.
_stdio_init,_stdio_term,_locale_init: make all hidden weak in common header
Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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This reverts commit 0d6ee549bc86fd330672a79d9a87d2c3825eea67.
We need to find a solution that will work in shared and static libraries
Signed-off-by: Austin Foxley <austinf@cetoncorp.com>
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Closes #2089 (https://bugs.busybox.net/show_bug.cgi?id=2089)
__errno_location / __h_errno_location access has to go through the PLT
like malloc/free, so the linuxthread variants gets used instead when
compiling with -pthread.
Based on http://github.com/mat-c/uClibc/commit/328d392c54aa5dc2b8e7f398a419087de497de2b
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Austin Foxley <austinf@cetoncorp.com>
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Signed-off-by: Khem Raj <raj.khem@gmail.com>
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sed -i -e '/Experimentally off - /d' $(grep -rl "Experimentally off - " *)
sed -i -e '/^\/\*[[:space:]]*libc_hidden_proto(/d' $(grep -rl "libc_hidden_proto" *)
should be a nop
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
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Appears to build fine (several .configs tried)
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situations
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to be weaks
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gone from libc. The remaining are left as exercise for others ;-)
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glibc 2.1.3 and ported to work with uClibc by Stefan Soucek and Erik Andersen
(me). Stefan has hacked things up such that linuxthreads runs on MMU-less
systems (tested only on arm-nommu). Erik cleaned things up and made it work
properly as a shared library.
-Erik
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