Bug 381411

Summary:

Odd g++ warning from pthread.h when compiling with -fno-exceptions

Product:

[Fedora] Fedora

Reporter:

Josh Boyer <jwboyer>

Component:

gcc

Assignee:

Jakub Jelinek <jakub>

Status:

CLOSED UPSTREAM

QA Contact:

Fedora Extras Quality Assurance <extras-qa>

Severity:

low

Docs Contact:

Priority:

low

Version:

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Hardware:

All

OS:

Linux

Whiteboard:

Fixed In Version:

Doc Type:

Bug Fix

Doc Text:

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Clone Of:

Environment:

Last Closed:

2007-11-21 08:53:01 UTC

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oVirt Team:

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RHEL 7.3 requirements from Atomic Host:

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Target Upstream Version:

Embargoed:

Attachments:

Description	Flags
small test app to try compiling	none

Description Josh Boyer 2007-11-14 02:29:42 UTC

Description of problem:

It seems that g++ will produce an odd warning when compiled with -fno-exceptions
for an application that uses pthread_cleanup_push.

Version-Release number of selected component (if applicable):

[jwboyer@vader ~]$ rpm -q gcc-c++
gcc-c++-4.1.2-33


How reproducible:

Always

Steps to Reproduce:
1.  Copy test program
2.  Build with:  g++ -O2 -Wall -fno-exceptions test.C -o foo -lpthread
3.
  
Actual results:

test.C: In member function ‘void foo::push(uint32_t)’:
test.C:22: warning: type-punning to incomplete type might break strict-aliasing
rules
test.C: In member function ‘void foo::pop(uint32_t&)’:
test.C:28: warning: type-punning to incomplete type might break strict-aliasing
rules


Expected results:

No warning?  Not sure exactly.

Additional info:

From what I can tell, pthread.h will use a __pthread_cleanup_class when building
C++ code normally.  However, when -fno-exceptions is passed, it expands the
macro to use a __pthread_unwind_buf_t used in conjunction with __sigsetjmp.

The warning seems to come from something to do with __sigsetjmp, but I can't
tell what exactly.

Comment 1 Josh Boyer 2007-11-14 02:31:34 UTC

Created attachment 257601 [details]
small test app to try compiling

Compiling this test app shows the warning when passing -fno-exceptions.  (Yes,
I know the application is stupid and broken.  It's only to illustrate the
warning that I can't figure out.)

[jwboyer@vader ~]$ g++ -O2 -Wall test.C -o foo -lpthread
[jwboyer@vader ~]$ g++ -O2 -Wall -fno-exceptions test.C -o foo -lpthread
test.C: In member function ‘void foo::push(uint32_t)’:
test.C:22: warning: type-punning to incomplete type might break strict-aliasing
rules
test.C: In member function ‘void foo::pop(uint32_t&)’:
test.C:28: warning: type-punning to incomplete type might break strict-aliasing
rules
[jwboyer@vader ~]$

Comment 2 Josh Boyer 2007-11-16 14:51:56 UTC

Ok, I can't figure out what the compiler is warning about.  I even tried using
-dD -E to get preprocessed output and that didn't lead me to any further
conclusions.

I'm not sure if this is a g++ bogus warning, or if something is truly broken here.

Comment 3 Josh Boyer 2007-11-19 21:37:47 UTC

This seems to happen on all of the more recent distros I've tried.  Perhaps an
upstream bug should be opened?  If so, should it be done against GCC or glibc?

Comment 4 Jakub Jelinek 2007-11-21 08:53:01 UTC

If you use cancellation, then it is terribly bad idea to compile with
-fno-exceptions.  That said, I have added an extra void * cast to shut up the
warnings with g++ 4.1/4.2, g++ 4.3 is smart enough not to warn in this case.

Comment 5 Josh Boyer 2007-11-21 14:49:29 UTC

(In reply to comment #4)
> If you use cancellation, then it is terribly bad idea to compile with
> -fno-exceptions.  That said, I have added an extra void * cast to shut up the
> warnings with g++ 4.1/4.2, g++ 4.3 is smart enough not to warn in this case.

Thanks Jakub.