Patchwork [RFC] powerpc: restore TOC when static longjmp to shared object

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Submitter rcardoso@linux.vnet.ibm.com
Date May 22, 2018, 6:40 p.m.
Message ID <4c67a306-d447-1158-1b92-22ed1cfcfa0a@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/27406/
State New
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rcardoso@linux.vnet.ibm.com - May 22, 2018, 6:40 p.m.
I've attached patch v2 to this email with the fixes suggested by Adhemerval.

One last issue is regard to the copyright on the tests. I put a 
copyright there but, the test is based on a test the user reported in 
bugzilla. I've adapted to libsupport and changed some of the code. What 
should I do in that case? I have to get the permission from the author 
first since the test is a derivative work? Some of the tests doesn't 
have copyright, and some of them mention the person who reports the test 
like stdio-common/tstscanf.c but I can't find a standard.


Em 16-05-2018 21:42, libc-alpha-digest-help@sourceware.org escreveu:
> 
> On 16/05/2018 16:36, Rogerio Alves wrote:
>> Attached to this email I am sending the first version of the patch but I have a problem with this patch. I can't make the test work. By some reason it can't find the .so needed by the test:
>>
>> FAIL:
>> ./setjmp-bug21895.so: cannot open shared object file: No such file or directory
>>
>> Notice that if I manually execute the command on make check stdout inside the folder it works fine. I'd appreciate any help on that.
>>
>> Regards
>>
>> Em 15-05-2018 17:48, Tulio Magno Quites Machado Filho escreveu:
>>> Florian Weimer<fw@deneb.enyo.de>  writes:
>>>
>>>> * Rogerio Alves:
>>>>
>>>>> One simple solution would be always restore the TOC pointer by uncomment
>>>>> the line bellow:
>>>>>
>>>>> /*     std r2,FRAME_TOC_SAVE(r1)       Restore the TOC save area.  */
>>>>>
>>>>> Or maybe we can check if we have a valid TOC pointer before restore it,
>>>>> instead #if defined SHARED.
>>>> Is the register reserved for the TOC pointer in static builds, too?
>>>> Then I suggest to unconditionally save nad restore it; not doing so
>>>> looks like a pointless micro-optimization.
>>>>
>>>> Another problem with sharing jump buffers across static dlopen is that
>>>> you might not have identical pointer guard values.
>>>>
>>>>> I would like to request for comments on this matter: Should we fix/work
>>>>> this? Is feasible to change longjmp to always restore TOC pointer?
>>>> Does setjmp already save it unonditionally?
>>>>
>>>> Removal of static dlopen is still some time away; it's likely not
>>>> going to happen in this cycle, and the fix looks simple enough.
>>> If static dlopen is still going to be supported for some cycles, I also agree
>>> it should be saved and restored unconditionally.
>>>
>> 0001-PATCH-v1-powerpc-Always-restore-TOC-on-longjmp.patch
>>
>>
>>  From eb9895f1548c8f6e1826095aee3221eaf9ce84c9 Mon Sep 17 00:00:00 2001
>> From: Rogerio Alves<rcardoso@linux.vnet.ibm.com>
>> Date: Wed, 16 May 2018 14:20:53 -0500
>> Subject: [PATCH] [PATCH v1] powerpc: Always restore TOC on longjmp.
>>
>> This patch change longjmp to always restore the TOC pointer (r2 register)
>> to the caller frame on powerpc. This is related to bug 21895[1] that reports
>> a situation where you have a static longjmp to a shared object file.
>>
>> [1]https://sourceware.org/bugzilla/show_bug.cgi?id=21895
> Please indicate where you actually tested this patch (since the make check
> is broken).
> 

I've fixed the test thanks to your suggestion.

>> 2018-05-16 Rogerio A. Cardoso<rcardoso@linux.vnet.ibm.com>
>>
>> 	*sysdeps/powerpc/powerpc64/__longjmp-common.S: Remove condition code for
>> 	restore r2 on longjmp.
>> 	*setjmp/Makefile: Include test build directives.
> You need to add each rules you might add, the ones you are changing, and
> removing (check other ChangeLog for example).
> 

Done.
>> 	*setjmp/setjmp-bug21895.c: new test file.
>> 	*setjmp/tst-setjmp-bug21895.c: new test file.
> Capitalize the new.
> 

Done.

>> ---
>>   setjmp/Makefile                              | 18 ++++++--
>>   setjmp/setjmp-bug21895.c                     | 42 ++++++++++++++++++
>>   setjmp/tst-setjmp-bug21895.c                 | 65 ++++++++++++++++++++++++++++
>>   sysdeps/powerpc/powerpc64/__longjmp-common.S |  5 +--
>>   4 files changed, 123 insertions(+), 7 deletions(-)
>>   create mode 100644 setjmp/setjmp-bug21895.c
>>   create mode 100644 setjmp/tst-setjmp-bug21895.c
>>
>> diff --git a/setjmp/Makefile b/setjmp/Makefile
>> index dc2fcc6..e715ee6 100644
>> --- a/setjmp/Makefile
>> +++ b/setjmp/Makefile
>> @@ -22,16 +22,28 @@ subdir	:= setjmp
>>   
>>   include ../Makeconfig
>>   
>> -headers	:= setjmp.h bits/setjmp.h bits/setjmp2.h
>> +headers	:= setjmp.h bits/setjmp.h bits/setjmp2.h bits/dlfcn.h dlfcn/dlfcn.h
> Why does it require adding more headers here? This is meant be installed afaik
> and I am not following the requirement here.
> 
>>   
>>   routines	:= setjmp sigjmp bsd-setjmp bsd-_setjmp \
>>   		   longjmp __longjmp jmp-unwind
>>   
>>   tests		:= tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
>> -		   tst-sigsetjmp tst-setjmp-static
>> +		   tst-sigsetjmp tst-setjmp-static tst-setjmp-bug21895
>> +
> Since the idea is test for static build I would recommend to follow the other
> static naming, i.e, tst-setjmp-bug21895-static.
> 

Done. Added static suffix.

>>   tests-static	:= tst-setjmp-static
>>   
>> +modules-names = setjmp-bug21895
>>   
>>   include ../Rules
>>   
>> -$(objpfx)tst-setjmp-fp: $(libm)
> I do not think you meant to remove this rule.
> 

It was not removed I've write the new rules before this rule. Anyway 
I've fixed it on v2.

>> +test-modules = $(addprefix $(objpfx),$(addsuffix .so,$(modules-names)))
>> +
>> +ifeq ($(build-shared),yes)
>> +tests: $(test-modules)
>> +endif
>> +
>> +$(objpfx)setjmp-bug21895.so: $(libdl)
>> +$(objpfx)tst-setjmp-bug21895: $(libdl)
>> +$(objpfx)tst-setjmp-bug21895.out: $(objpfx)setjmp-bug21895.so
>> +
>> +$(objpfx)ts-tsetjmp-fp: $(libm)
> I think the idea is to build the test even if build-shared is set to no (since
> you are testing static linking).  I think what you want is:
> 
> ---
> 
> diff --git a/setjmp/Makefile b/setjmp/Makefile
> index dc2fcc6..231474b 100644
> --- a/setjmp/Makefile
> +++ b/setjmp/Makefile
> @@ -28,10 +28,17 @@ routines    := setjmp sigjmp bsd-setjmp bsd-_setjmp \
>                     longjmp __longjmp jmp-unwind
> 
>   tests          := tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
> -                  tst-sigsetjmp tst-setjmp-static
> -tests-static   := tst-setjmp-static
> +                  tst-sigsetjmp tst-setjmp-static tst-setjmp-bug21895-static
> 
> +tests-static   := tst-setjmp-static tst-setjmp-bug21895-static
> +
> +modules-names = setjmp-bug21895
> 
>   include ../Rules
> 
>   $(objpfx)tst-setjmp-fp: $(libm)
> +$(objpfx)tst-setjmp-bug21895-static: $(common-objpfx)dlfcn/libdl.a
> +$(objpfx)tst-setjmp-bug21895-static.out: $(objpfx)setjmp-bug21895.so
> +
> +tst-setjmp-bug21895-static-ENV = \
> +  LD_LIBRARY_PATH=$(objpfx):$(common-objpfx):$(common-objpfx)setjmp:$(common-objpfx)elf
> 
> ---
> 
> At least with qemu-static it seems to work with your patch.
> 
> 

Thanks to your help it's working now. That's exactly what I wanted.

>> diff --git a/setjmp/setjmp-bug21895.c b/setjmp/setjmp-bug21895.c
>> new file mode 100644
>> index 0000000..d6f5516
>> --- /dev/null
>> +++ b/setjmp/setjmp-bug21895.c
>> @@ -0,0 +1,42 @@
>> +/* Copyright (C) 2013-2018 Free Software Foundation, Inc.
> Wrong Copyright date span and missing one line description.
> 
Fixed.
>> +   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/>.  */
>> +
>> +/* Test that setjmp/longjmp interoperability with static dlopen.
>> +   Bugzila #21895.  */
>> +#include <alloca.h>
>> +#include <string.h>
>> +#include <setjmp.h>
>> +
>> +jmp_buf jb;
>> +void (*bar)(jmp_buf);
>> +
>> +void
>> +lbar (int i, ...)
>> +{
>> +  bar(jb);
>> +  for(;;);
>> +}
>> +
>> +void
>> +foo (void)
>> +{
>> +  int i = setjmp(jb);
>> +  char *c = alloca(256);
>> +  memset(c, 0, 256);
>> +  lbar(i);
>> +  for(;;);
>> +}
>> diff --git a/setjmp/tst-setjmp-bug21895.c b/setjmp/tst-setjmp-bug21895.c
>> new file mode 100644
>> index 0000000..5333494
>> --- /dev/null
>> +++ b/setjmp/tst-setjmp-bug21895.c
>> @@ -0,0 +1,65 @@
>> +/* Copyright (C) 2013-2018 Free Software Foundation, Inc.
> Wrong Copyright date span and missing one line description.
> 
Fixed.
>> +   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/>.  */
>> +
>> +/* Test that setjmp/longjmp interoperability with static dlopen.
>> +   Bugzila #21895.  */
>> +
>> +#include <setjmp.h>
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <dlfcn.h>
>> +
>> +static void
>> +bar (jmp_buf jb)
>> +{
>> +  static int i;
>> +  if (i++==1) exit(0);
>> +  longjmp(jb, i);
>> +}
>> +
>> +static int
>> +do_test (void)
>> +{
>> +  void *h = dlopen("./setjmp-bug21895.so", RTLD_NOW);
> Better to just use name, since on test environment variable in Makefile
> change I proposed the path to build setjmp folder is already on the
> LD_LIBRARY_PATH list.
> 
>> +  if (!h) {
>> +    puts ("FAIL: ");
>> +    puts (dlerror());
>> +    return 1;
>> +  }
> Wrong indentation and please use libsupport macros.
> 

Fixed. Using libsupport now.
>> +
>> +  void (*pfoo)(void) = dlsym(h, "foo");
>> +  if (!pfoo) {
>> +    puts ("FAIL: ");
>> +    puts (dlerror());
>> +    return 1;
>> +  }
>> +
>> +  void (**ppbar)(jmp_buf) = dlsym(h, "bar");
>> +  if (!ppbar) {
>> +    puts ("FAIL: ");
>> +    puts (dlerror());
>> +    return 1;
>> +  }
>> +
>> +  *ppbar = bar;
>> +  pfoo();
>> +
>> +  for(;;);
>> +}
>> +
>> +#define TEST_FUNCTION do_test ()
>> +#include "../test-skeleton.c"
> We do not use test-skeleton.c inclusion any longer, use libsupport
> (support/test-driver.c).
> 

Done.

>> diff --git a/sysdeps/powerpc/powerpc64/__longjmp-common.S b/sysdeps/powerpc/powerpc64/__longjmp-common.S
>> index 0e10b8d..a5973c9 100644
>> --- a/sysdeps/powerpc/powerpc64/__longjmp-common.S
>> +++ b/sysdeps/powerpc/powerpc64/__longjmp-common.S
>> @@ -130,9 +130,6 @@ L(no_vmx):
>>   	ld r0,(JB_LR*8)(r3)
>>   	ld r14,((JB_GPRS+0)*8)(r3)
>>   	lfd fp14,((JB_FPRS+0)*8)(r3)
>> -#if defined SHARED && !IS_IN (rtld)
>> -	std r2,FRAME_TOC_SAVE(r1)	/* Restore the callers TOC save area.  */
>> -#endif
>>   	ld r15,((JB_GPRS+1)*8)(r3)
>>   	lfd fp15,((JB_FPRS+1)*8)(r3)
>>   	ld r16,((JB_GPRS+2)*8)(r3)
>> @@ -152,7 +149,7 @@ L(no_vmx):
>>   	second argument (-4@4), and target address (8@0), respectively.  */
>>   	LIBC_PROBE (longjmp, 3, 8@3, -4@4, 8@0)
>>   	mtlr r0
>> -/* 	std r2,FRAME_TOC_SAVE(r1)	Restore the TOC save area.  */
>> + 	std r2,FRAME_TOC_SAVE(r1)	/* Restore the TOC save area.  */
> Space before tab in indent.
>

Done.

>>   	ld r21,((JB_GPRS+7)*8)(r3)
>>   	lfd fp21,((JB_FPRS+7)*8)(r3)
>>   	ld r22,((JB_GPRS+8)*8)(r3)
>> -- 2.7.4
>>
Alexander Monakov - May 23, 2018, 9:26 a.m.
On Tue, 22 May 2018, Rogerio Alves wrote:

> I've attached patch v2 to this email with the fixes suggested by Adhemerval.

Why was it necessary to change the prototype of lbar(), and does the testcase
still demonstrate the issue with that change (does it fail without the patch)?

Note that as soon as gcc is capable of optimizing out the alloca-memset code
in the testcase, it will no longer serve the purpose (maybe it's already
capable, when preparing the testcase I only checked -O0 IIRC). Surely there
are more direct and robust ways of checking that TOC is correctly restored?

Alexander
rcardoso@linux.vnet.ibm.com - May 23, 2018, 12:33 p.m.
Em 23-05-2018 06:26, Alexander Monakov escreveu:
> On Tue, 22 May 2018, Rogerio Alves wrote:
> 
>> I've attached patch v2 to this email with the fixes suggested by Adhemerval.
> 
> Why was it necessary to change the prototype of lbar(), and does the testcase
> still demonstrate the issue with that change (does it fail without the patch)?
> 

Yes it fails without the patch.

The change on lbar() prototype was made only because glibc is being 
compiled with and it give me an error due a  -Werror=strict-prototypes. 
But lbar(void) works fine but, you don't have a segmentation fault.

The problem is that if you have a parameter area on the stack 
alloca/memset will set TOC to 0x0 and lbar() prototype doesn't mean "no 
parameters" in C it means "any arguments" - C Standard, subclause 
6.7.6.3, paragraph 14 [ISO/IEC 9899:2011] - so the compiler ends up 
creating a parameter area for the function.

This code works if you use lbar(void) or if you don't have a parameter 
save area on stack:

lbar() - Segmentation fault
lbar(void) - Works (no arguments).
lbar(int a, int b, int c, int d, int e, int f, int g) - Works (less than 
8 parameters, use registers, no parameter saving area)
lbar(int a, int b, int c, int d, int e, int f, int g, int h, int i) - 
Segmentation fault


> Note that as soon as gcc is capable of optimizing out the alloca-memset code
> in the testcase, it will no longer serve the purpose (maybe it's alread > capable, when preparing the testcase I only checked -O0 IIRC). Surely 
there
> are more direct and robust ways of checking that TOC is correctly restored?
> 
I've tested with -O3 here and get the same problem here. If 
alloca/memset is optimized out or removed from the code the problem 
doesn't happens but, that's only if the caller stack frame doesn't 
change if don't, when longjmp execute you still have a valid TOC on the 
stack.

But described in https://sourceware.org/bugzilla/show_bug.cgi?id=269

"In this (simple) case the appl calls [bsd]_setjmp() which transfers to 
__setjmp.  Both are in libc.so.  So by the time __setjmp() gets control 
libc.so's TOC is already loaded.  In this case we need to reach back 
into the  callers frame and retrieve the callers TOC from the TOC save 
area. But in the static case the TOC is not saved and has not changed.

In GLIBC sysdeps/powerpc/powerpc64/setjmp.S is built 4 times (static, 
shared, profiled, and a special version (rtld-setjmp) for the dynamic 
linker.  In the  SHARED case (libc.so), external calls to setjmp will 
save the TOC on the stack, but internal libc calls will not.  So the 
trick is to do the correct thing for each case."

So your test has a example of a code that use a static function to call 
a longjmp that was set on a shared object called via (static) dlopen. In 
that case we should have to restore it to caller frame as the jump area 
is in shared object but, since longjmp is inside static compiled unit 
TOC is not restored.

I don't think that alloca/memset should destroy the caller stack like is 
happening but, also I think we have to restore TOC to the caller frame 
after the longjmp in that case also. I don't know if there's any other 
more direct and robust ways to checking if TOC is correctly restored. I 
can't think in anything easier than always restore.

Rogerio


> Alexander
>
Tulio Magno Quites Machado Filho - May 23, 2018, 1:33 p.m.
Rogerio Alves <rcardoso@linux.vnet.ibm.com> writes:

> I don't think that alloca/memset should destroy the caller stack like is 
> happening but, also I think we have to restore TOC to the caller frame 
> after the longjmp in that case also.

Do we have a bug report for this?
If not, we need one.
Alexander Monakov - May 23, 2018, 2:24 p.m.
On Wed, 23 May 2018, Rogerio Alves wrote:
> I don't think that alloca/memset should destroy the caller stack like is
> happening but, also I think we have to restore TOC to the caller frame after
> the longjmp in that case also. I don't know if there's any other more direct
> and robust ways to checking if TOC is correctly restored. I can't think in
> anything easier than always restore.

I'm not challenging the idea that "always restoring" is an appropriate fix.
My question was about *verifying* that TOC register is restored as it ought
to, i.e. how the testcase needs to work. Right now, the test uses my code
from Bugzilla that worked okay for demonstration purposes, but has issues as
a long-term testsuite addition:

* it demonstrates the issue in a very intransparent fashion, relying on
  non-obvious interaction with alloca-memset part of the test;

* when GCC manages to optimize out the alloca-memset part, the test
  will cease to work for the intended purpose.

Alexander
rcardoso@linux.vnet.ibm.com - May 25, 2018, 7:39 p.m.
Em 23-05-2018 11:24, Alexander Monakov escreveu:
> On Wed, 23 May 2018, Rogerio Alves wrote:
>> I don't think that alloca/memset should destroy the caller stack like is
>> happening but, also I think we have to restore TOC to the caller frame after
>> the longjmp in that case also. I don't know if there's any other more direct
>> and robust ways to checking if TOC is correctly restored. I can't think in
>> anything easier than always restore.
> 
> I'm not challenging the idea that "always restoring" is an appropriate fix.
> My question was about *verifying* that TOC register is restored as it ought
> to, i.e. how the testcase needs to work. Right now, the test uses my code
> from Bugzilla that worked okay for demonstration purposes, but has issues as
> a long-term testsuite addition:
>
> * it demonstrates the issue in a very intransparent fashion, relying on
>    non-obvious interaction with alloca-memset part of the test;
> 
> * when GCC manages to optimize out the alloca-memset part, the test
>    will cease to work for the intended purpose.
> 
> Alexander
> 

Ok. I understand your concern. Let me see if I can change this test to 
check if the TOC was been restored.

Rogerio

Patch

From 989f90132a77d8f1199881d88f51384f25d452fb Mon Sep 17 00:00:00 2001
From: Rogerio Alves <rcardoso@linux.vnet.ibm.com>
Date: Wed, 16 May 2018 14:20:53 -0500
Subject: [PATCH v2] powerpc: Always restore TOC on longjmp.

This patch change longjmp to always restore the TOC pointer (r2 register)
to the caller frame on powerpc. This is related to bug 21895[1] that reports
a situation where you have a static longjmp to a shared object file.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=21895

2018-05-16 Rogerio A. Cardoso <rcardoso@linux.vnet.ibm.com>

	*sysdeps/powerpc/powerpc64/__longjmp-common.S: Remove condition code for
	restore r2 on longjmp.
	*setjmp/Makefile: Added tst-setjmp-bug21895-static to test list.
	Added rules to build test tst-setjmp-bug21895-static
	Added module setjmp-bug21895 and rules to build a shared object from it.
	*setjmp/setjmp-bug21895.c: New test file.
	*setjmp/tst-setjmp-bug21895-static.c: New test file.
---
 Changes in v2: Per Adhemerval Zanella. Fix test fail using the suggestions
given. Fix changelog. Fix copyright and indentation for new tests. Change
tests to use libsupport instead old test-skeleton. Fix a extra space
in  __longjmp-common.

 setjmp/Makefile                              | 16 ++++++-
 setjmp/setjmp-bug21895.c                     | 44 ++++++++++++++++++
 setjmp/tst-setjmp-bug21895-static.c          | 67 ++++++++++++++++++++++++++++
 sysdeps/powerpc/powerpc64/__longjmp-common.S |  5 +--
 4 files changed, 127 insertions(+), 5 deletions(-)
 create mode 100644 setjmp/setjmp-bug21895.c
 create mode 100644 setjmp/tst-setjmp-bug21895-static.c

diff --git a/setjmp/Makefile b/setjmp/Makefile
index dc2fcc6..d70daa2 100644
--- a/setjmp/Makefile
+++ b/setjmp/Makefile
@@ -29,9 +29,23 @@  routines	:= setjmp sigjmp bsd-setjmp bsd-_setjmp \
 
 tests		:= tst-setjmp jmpbug bug269-setjmp tst-setjmp-fp \
 		   tst-sigsetjmp tst-setjmp-static
-tests-static	:= tst-setjmp-static
 
+tests-static	:= tst-setjmp-static tst-setjmp-bug21895-static
+
+modules-names = setjmp-bug21895
 
 include ../Rules
 
 $(objpfx)tst-setjmp-fp: $(libm)
+
+test-modules = $(addprefix $(objpfx),$(addsuffix .so,$(modules-names)))
+
+ifeq ($(build-shared),yes)
+tests: $(test-modules)
+endif
+
+$(objpfx)tst-setjmp-bug21895-static: $(common-objpfx)dlfcn/libdl.a
+$(objpfx)tst-setjmp-bug21895-static.out: $(objpfx)setjmp-bug21895.so
+
+tst-setjmp-bug21895-static-ENV = \
+	LD_LIBRARY_PATH=$(objpfx):$(common-objpfx):$(common-objpfx)setjmp:$(common-objpfx)elf
diff --git a/setjmp/setjmp-bug21895.c b/setjmp/setjmp-bug21895.c
new file mode 100644
index 0000000..f8f3016
--- /dev/null
+++ b/setjmp/setjmp-bug21895.c
@@ -0,0 +1,44 @@ 
+/* Shared object part of test for setjmp interoperability with static
+   dlopen BZ #21895.
+   Copyright (C) 2017-2018 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 <alloca.h>
+#include <string.h>
+#include <setjmp.h>
+
+jmp_buf jb;
+void (*bar)(jmp_buf);
+
+void
+lbar (int i, ...)
+{
+  bar(jb);
+  for(;;);
+}
+
+void
+foo (void)
+{
+  int i = setjmp(jb);
+  char *c = alloca(256);
+  memset(c, 0, 256);
+
+  lbar(i);
+
+  for(;;);
+}
diff --git a/setjmp/tst-setjmp-bug21895-static.c b/setjmp/tst-setjmp-bug21895-static.c
new file mode 100644
index 0000000..5338499
--- /dev/null
+++ b/setjmp/tst-setjmp-bug21895-static.c
@@ -0,0 +1,67 @@ 
+/* Test setjmp interoperability with static dlopen BZ #21895.
+   Copyright (C) 2017-2018 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 <setjmp.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <dlfcn.h>
+
+static void
+bar (jmp_buf jb)
+{
+  static int i;
+  if (i++==1)
+    exit(0);	/* Success.  */
+
+  longjmp(jb, i);
+}
+
+static int
+do_test (void)
+{
+  void *h = dlopen("setjmp-bug21895.so", RTLD_NOW);
+  if (!h)
+    {
+      puts(dlerror());
+      return 1;
+    }
+
+  void (*pfoo)(void) = dlsym(h, "foo");
+  if (!pfoo)
+    {
+      puts(dlerror());
+      return 1;
+    }
+
+  void (**ppbar)(jmp_buf) = dlsym(h, "bar");
+  if (!ppbar)
+    {
+      puts(dlerror());
+      return 1;
+    }
+
+  *ppbar = bar;
+  pfoo();
+
+  for(;;);
+}
+
+/* Make sure the test will not stuck if jmp fails and fall into one of
+   for(;;).  */
+#define TIMEOUT 100
+#include <support/test-driver.c>
diff --git a/sysdeps/powerpc/powerpc64/__longjmp-common.S b/sysdeps/powerpc/powerpc64/__longjmp-common.S
index 0e10b8d..99c17c5 100644
--- a/sysdeps/powerpc/powerpc64/__longjmp-common.S
+++ b/sysdeps/powerpc/powerpc64/__longjmp-common.S
@@ -130,9 +130,6 @@  L(no_vmx):
 	ld r0,(JB_LR*8)(r3)
 	ld r14,((JB_GPRS+0)*8)(r3)
 	lfd fp14,((JB_FPRS+0)*8)(r3)
-#if defined SHARED && !IS_IN (rtld)
-	std r2,FRAME_TOC_SAVE(r1)	/* Restore the callers TOC save area.  */
-#endif
 	ld r15,((JB_GPRS+1)*8)(r3)
 	lfd fp15,((JB_FPRS+1)*8)(r3)
 	ld r16,((JB_GPRS+2)*8)(r3)
@@ -152,7 +149,7 @@  L(no_vmx):
 	second argument (-4@4), and target address (8@0), respectively.  */
 	LIBC_PROBE (longjmp, 3, 8@3, -4@4, 8@0)
 	mtlr r0
-/* 	std r2,FRAME_TOC_SAVE(r1)	Restore the TOC save area.  */
+	std r2,FRAME_TOC_SAVE(r1)	/* Restore the TOC save area.  */
 	ld r21,((JB_GPRS+7)*8)(r3)
 	lfd fp21,((JB_FPRS+7)*8)(r3)
 	ld r22,((JB_GPRS+8)*8)(r3)
-- 
2.7.4