[Bug libgcc/56846] New: _Unwind_Backtrace on ARM and noexcept

[Bug libgcc/56846] New: _Unwind_Backtrace on ARM and noexcept

[npl at chello dot at]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

             Bug #: 56846
           Summary: _Unwind_Backtrace on ARM and noexcept
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgcc
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: npl@chello.at


I want to inquire about the feasibility of using _Unwind_Backtrace on ARM,
particularly in combination with the noexcept keyword.
Since the backtrace depends on the unwind information, it seems the
_Unwind_Backtrace breaks down when encountering "noexcept" functions.
Whats even worse is, that instead of just stopping, _Unwind_Backtrace will just
infinitely report the last context (unless the the callback tells to stop).

So there are two points I guess, first that the _Unwind_Backtrace should stop
when it cant proceed further instead of looping forever. I suppose thats a bug.

Then I`d ask if its somehow possible to still backtrace through noexcept
functions, perhaps with a compiler switch that still generates the necessary
unwind tables and/or manual adjustment to the personality routine. (gdb can
generate the traces... so I guess it must be possible)

I am using an arm-none-eabi toolchain, of version 4.7.2. 
----------------------------------------------------------------
Using built-in specs.
COLLECT_GCC=arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/opt/hipase-imx28-v0/libexec/gcc/arm-none-eabi/4.7.2/lto-wrapper
Target: arm-none-eabi
Configured with: /opt/hipase-imx28-v0/src/gcc-4.7.2/configure
--prefix=/opt/hipase-imx28-v0 --target=arm-none-eabi --enable-languages=c,c++
--disable-libstdcxx-verbose --disable-libmudflap --disable-libssp
--disable-libstdcxx-pch --enable-multilib --disable-shared --disable-nls
--with-system-zlib --enable-tls --enable-gold --with-gnu-as --with-gnu-ld
--enable-lto --with-newlib
--with-gmp=/home/tcbuild/toolchain-make/build/ggcnativebuild/gmp-5.0.5
--with-mpfr=/home/tcbuild/toolchain-make/build/ggcnativebuild/mpfr-3.1.1
--with-mpc=/home/tcbuild/toolchain-make/build/ggcnativebuild/mpc-1.0.1
--with-cloog=/home/tcbuild/toolchain-make/build/ggcnativebuild/cloog-ppl-0.15.11
--with-ppl=/home/tcbuild/toolchain-make/build/ggcnativebuild/ppl-0.11
--with-host-libstdcxx='-Wl,-Bstatic,/usr/lib/gcc/i486-linux-gnu/4.4.5/libstdc++.a,/usr/lib/gcc/i486-linux-gnu/4.4.5/libsupc++.a,-Bdynamic
-lm'
Thread model: single
gcc version 4.7.2 (GCC)

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[joey.ye at arm dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

Joey Ye <joey.ye at arm dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |joey.ye at arm dot com

--- Comment #1 from Joey Ye <joey.ye at arm dot com> ---
I cannot reproduce the issue you described with my arm-none-eabi GCC 4.7.4.
Here is my case:

#include <stdio.h>
void foo() noexcept
{
        printf("This is in foo\n");
}

void bar() noexcept
{
        printf("This is in bar\n");
        foo();
}

int main()
{
        bar();  
        return 0;
}

When I break and stp at foo, here is the successful backtrace:
(gdb) back
#0  foo () at n.cpp:4
#1  0x000081e0 in bar () at n.cpp:10
#2  0x000081ec in main () at n.cpp:15

Can you please share a small case to reproduce the issue?

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[npl at chello dot at]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #2 from npl at chello dot at ---
I cant easily make a simple reproducible testcase as this is a custom realtime
OS for a very specific CPU. And I can only test this example next week at work
where I have hardware to run it.

And I certainly wasnt talking about debugging with gdb (which uses some rather
advanced heuristics AFAIK), but the library funtions within libgcc (unwind.h
header). I reworked your example to show the issue: 

#include <unwind.h>
#include <iostream>

_Unwind_Reason_Code trace_func(struct _Unwind_Context * context, void* arg)
{
  void *ip = (void *)_Unwind_GetIP(context);
  /* I have a check here to test if the ip is the same as last time, else this
would be called endlessly */
  std::cout << "Address: " << ip << std::endl;
  return _URC_NO_REASON;
}


void bar()
{
        std::cout << "This is in bar" << std::endl;
        _Unwind_Backtrace((_Unwind_Trace_Fn)&trace_func, nullptr);
}

void foo() noexcept
{
        bar();
}

int main()
{
        foo();  
        return 0;
}

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[joey.ye at arm dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #3 from Joey Ye <joey.ye at arm dot com> ---
I can reproduce it now. Thanks!

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[npl at chello dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #4 from npl at chello dot at ---
I just found the similar entry on launchpad.
I have to recall this from memory, as its been a long time since I played
around with it.

The issue of repeating entries occurs if you have a function wihout
stack-unwinding information. These are as far as I know:
* .cantunwind in asm, probably plain asm too
* "C compiled" compiled without flags to generate unwind tables
* C++ compiled function with noexcept

Further, the compiled code behaves right when exceptions are thrown
(std::terminate), so the tables and generated code should be fine. The issue
should thus be in libgcc`s implementation of the _Unwind_Backtrace function.

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[ramana at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-05-16
                 CC|                            |ramana at gcc dot gnu.org
     Ever confirmed|0                           |1

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[joey.ye at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #5 from Joey Ye <joey.ye at arm dot com> ---
This issue was predicted back to when _Unwind_Backtrace was enabled on ARM.
http://gcc.gnu.org/ml/gcc/2007-08/msg00235.html

"This will keep going if the personality routine returns _URC_FAILURE.
Do you need anything besides _URC_CONTINUE_UNWIND?  The personality
routine in libsupc++ for ARM will return _URC_HANDLER_FOUND even
during forced unwinding but that seems like a bug now that you've
given a meaning to _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND."

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[tony.wang at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

wangzheyu <tony.wang at arm dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tony.wang at arm dot com

--- Comment #6 from wangzheyu <tony.wang at arm dot com> ---
Confirmed on arm tagret, and there's an old discussion on this:
http://gcc.gnu.org/ml/gcc/2007-08/msg00235.html. I'm working on a patch to fix
this.

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[tony.wang at arm dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #7 from wangzheyu <tony.wang at arm dot com> ---
Another test case doesn't involve noexcept key workd.

Cmd line: arm-none-eabi-g++ -mthumb -mcpu=cortex-m3 -O0 -g -std=c++11
-specs=rdimon.specs main.c -o main.exe

#include <unwind.h>
#include <stdio.h>
_Unwind_Reason_Code trace_func(struct _Unwind_Context * context, void* arg) {
  void *ip = (void *)_Unwind_GetIP(context);
  printf("Address: %p\n", ip);
  return _URC_NO_REASON;
}
void bar()
{
        puts("This is in bar");
        _Unwind_Backtrace((_Unwind_Trace_Fn)&trace_func, 0);
}
void foo()
{
  try
  {
    bar();
  }
  catch (...)
  {
    puts("Exception");
  }
}

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #8 from thopre01 at gcc dot gnu.org ---
Author: thopre01
Date: Wed Sep 10 04:45:32 2014
New Revision: 215101

URL: https://gcc.gnu.org/viewcvs?rev=215101&root=gcc&view=rev
Log:
2014-09-10  Tony Wang  <tony.wang@arm.com>

    libstdc++-v3/
    PR target/56846
    * libsupc++/eh_personality.cc (PERSONALITY_FUNCTION):
    Return with CONTINUE_UNWINDING when the state pattern
    contains: _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/libsupc++/eh_personality.cc

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[yroux at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #9 from Yvan Roux <yroux at gcc dot gnu.org> ---
Author: yroux
Date: Mon Oct  6 12:25:14 2014
New Revision: 215929

URL: https://gcc.gnu.org/viewcvs?rev=215929&root=gcc&view=rev
Log:
/libstdc++-v3/
2014-10-06  Yvan Roux  <yvan.roux@linaro.org>

    Backport from trunk r215101.
    2014-09-10  Tony Wang  <tony.wang@arm.com>

    PR target/56846
    * libsupc++/eh_personality.cc (PERSONALITY_FUNCTION):
    Return with CONTINUE_UNWINDING when the state pattern
    contains: _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND


Modified:
    branches/linaro/gcc-4_9-branch/libstdc++-v3/ChangeLog.linaro
    branches/linaro/gcc-4_9-branch/libstdc++-v3/libsupc++/eh_personality.cc

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[npl at chello dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #10 from npl at chello dot at ---
Hi,

thanks for the fix, any chance of adding this to 4.9 and 4.8 aswell?

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #11 from thopre01 at gcc dot gnu.org ---
(In reply to Yvan Roux from comment #9)
> Author: yroux
> Date: Mon Oct  6 12:25:14 2014
> New Revision: 215929
> 
> URL: https://gcc.gnu.org/viewcvs?rev=215929&root=gcc&view=rev
> Log:
> /libstdc++-v3/
> 2014-10-06  Yvan Roux  <yvan.roux@linaro.org>
> 
> 	Backport from trunk r215101.
> 	2014-09-10  Tony Wang  <tony.wang@arm.com>
> 
> 	PR target/56846
> 	* libsupc++/eh_personality.cc (PERSONALITY_FUNCTION):
> 	Return with CONTINUE_UNWINDING when the state pattern
> 	contains: _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND
> 
> 
> Modified:
>     branches/linaro/gcc-4_9-branch/libstdc++-v3/ChangeLog.linaro
>     branches/linaro/gcc-4_9-branch/libstdc++-v3/libsupc++/eh_personality.cc


Any chance you could backport for 4.8 Yvan? Do you want me to do it? Or are the
release manager against a 4.8 backport?

Best regards,

Thomas
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Subject: [Bug tree-optimization/63836] [5 Regression] r217349 caused segfault building 178.galgel from cpu2000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc836

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
A simple testcase:

[hjl@gnu-mic-2 delta-fortran]$ cat foo.f90
      SUBROUTINE DTRSM ( NN, NB)
         DO 50 J = NN, 1, -NB
   50    CONTINUE
      end
[hjl@gnu-mic-2 delta-fortran]$
/export/project/git/gcc-regression/master/217349/usr/bin/gfortran -ffixed-form
-ffixed-line-length-132 -DSPEC_CPU2000_LP64 -ffast-math -S  foo.f90 -O2
foo.f90:4:0:

       end
 ^
Error: non-trivial conversion at assignment
unsigned int
integer(kind=4)
_13 = _7;
foo.f90:4:0: internal compiler error: verify_gimple failed
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[yroux at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #12 from Yvan Roux <yroux at gcc dot gnu.org> ---
Hi Thomas,

> Any chance you could backport for 4.8 Yvan? Do you want me to do it? Or are
> the release manager against a 4.8 backport?

Do you mean Linaro 4.8 branch ? if it is the case I'll not be able to do it
before tomorrow (which is our deadline for our 2014.11 source release).

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #13 from thopre01 at gcc dot gnu.org ---
(In reply to Yvan Roux from comment #12)
> Hi Thomas,
> 
> > Any chance you could backport for 4.8 Yvan? Do you want me to do it? Or are
> > the release manager against a 4.8 backport?
> 
> Do you mean Linaro 4.8 branch ? if it is the case I'll not be able to do it
> before tomorrow (which is our deadline for our 2014.11 source release).

No I meant FSF 4.8 branch. The bug log only show a commit to trunk and GCC 4.9
FSF branch.

Best regards.

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #15 from thopre01 at gcc dot gnu.org ---
I'll take care of it.

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #16 from thopre01 at gcc dot gnu.org ---
Author: thopre01
Date: Thu Nov 27 13:58:35 2014
New Revision: 218126

URL: https://gcc.gnu.org/viewcvs?rev=218126&root=gcc&view=rev
Log:
2014-11-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    Backport from mainline
    2014-09-10  Tony Wang  <tony.wang@arm.com>

    PR target/56846
    * libsupc++/eh_personality.cc (PERSONALITY_FUNCTION):
    Return with CONTINUE_UNWINDING when the state pattern
    contains: _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND

Modified:
    branches/gcc-4_9-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_9-branch/libstdc++-v3/libsupc++/eh_personality.cc

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

--- Comment #17 from thopre01 at gcc dot gnu.org ---
Author: thopre01
Date: Thu Nov 27 14:10:10 2014
New Revision: 218127

URL: https://gcc.gnu.org/viewcvs?rev=218127&root=gcc&view=rev
Log:
2014-11-27  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    Backport from mainline
    2014-09-10  Tony Wang  <tony.wang@arm.com>

    PR target/56846
    * libsupc++/eh_personality.cc (PERSONALITY_FUNCTION):
    Return with CONTINUE_UNWINDING when the state pattern
    contains: _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND

Modified:
    branches/gcc-4_8-branch/libstdc++-v3/ChangeLog
    branches/gcc-4_8-branch/libstdc++-v3/libsupc++/eh_personality.cc

[Bug libgcc/56846] _Unwind_Backtrace on ARM and noexcept

[thopre01 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56846

thopre01 at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #18 from thopre01 at gcc dot gnu.org ---
Fixed in all currently supported branches