Bug 433543 - simple program compiled with gcc -O2 -pthread segfaults on exit
simple program compiled with gcc -O2 -pthread segfaults on exit
Status: CLOSED NOTABUG
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: gcc (Show other bugs)
5.1
x86_64 Linux
low Severity medium
: rc
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Assigned To: Jakub Jelinek
BaseOS QE
:
Depends On:
Blocks:
  Show dependency treegraph
 
Reported: 2008-02-19 17:04 EST by Joe Korty
Modified: 2013-11-26 13:31 EST (History)
1 user (show)

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Doc Type: Bug Fix
Doc Text:
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Last Closed: 2013-11-26 13:31:34 EST
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Attachments (Terms of Use)
short multithreaded C program (656 bytes, text/x-csrc)
2008-02-19 17:04 EST, Joe Korty
no flags Details

  None (edit)
Description Joe Korty 2008-02-19 17:04:50 EST
Description of problem:
The attached 32-line C program segfaults on exit when it is compiled
with -O2 -pthread.  It works fine if 1) -O1 is used, or 2) the return
is replaced with an exit(0), or 3) it is compiled on a RHEL 4 system with
-O2 -pthread, the binary moved over to a RHEL 5 system and executed there.


Version-Release number of selected component (if applicable):
gcc version 4.1.2 20070626 (Red Hat 4.1.2-14)
glibc-2.5-18

How reproducible:
Every time.


Steps to Reproduce:
1. Get an x86_64 smp box
2. Install 64 bit RHEL 5.1
3. yum update
4. compile with -O2 -pthread the given test program
5. run program.  It will segfault on return from main().
  
Actual results:
Exiting...
Segmentation fault


Expected results:
Exiting...


Additional info:
Comment 1 Joe Korty 2008-02-19 17:04:50 EST
Created attachment 295347 [details]
short multithreaded C program
Comment 2 Jeff Law 2013-11-26 13:31:34 EST
Your program is buggy.

The fundamental problem is th_ret is defined as an integer, which is 4 bytes. You take the address of th_ret, cast it to a void * and pass that to pthread_join.  pthread_join.  pthread_join expects a void** and will write a pointer sized value.

The size a pointer is larger than an integer, this results in pthread_join writing out of the memory space occupied by th_ret and stomps on the stack resulting in a segfault when the optimizer is enabled.  WIthout the optimizer, your code still stomps on the stack, but it does not clobber a critical memory location.

Pass a pointer to a correctly sized object to pthread_join and this will (of course) work fine.

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