?
Solved

Segmentation fault accessing local variables

Posted on 2013-05-17
7
Medium Priority
?
500 Views
Last Modified: 2013-05-20
Hello There Experts,

I'm seeing a very strange problem with my multi-threaded C++ application. After calling a certain function (in main()) I can no longer access any local (stack) variables without getting a segmentation fault. Also, calling return() produces the same results. Moving the variables to the heap makes it run. The function called is not passed any of the local variables, but it does create several new threads. I'm suspecting stack corruption, so got the stack pointer using 'register int stackp asm("r1")' and printed out 50 nearest dwords with addresses higher than the stack pointer, but its the same. I set a local variable to a specific value and was able to see it in the print-out, so my method looks like its right.

I'm a C-guy so I'm not sure if I'm missing some C++ thing here or what's going on.

Any advice or help is appreciated,

Thanks

/SC

Btw, I'm using the following

ARCH: Microblaze
Linux 3.6.0
GCC 4.6.4
Binutils  2.22.90
egLibc 2.14.90
0
Comment
Question by:sctccomm
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
  • 2
7 Comments
 
LVL 86

Expert Comment

by:jkr
ID: 39176409
Could you post the code?
0
 

Author Comment

by:sctccomm
ID: 39176436
I wish, its 5 megabytes of fairly complicated source code. I'll try to distill it down.

I did discover something new though. I'm no expert on this but looking at the assembly code it looks like r19 is used to point to the stack base. The problem is that this value's most significant byte is wiped out after calling that function I mentioned earlier.

R19 Before: 0xbf945db8
R19 After:   0x00945db8

The crash happens as soon as a "load word immediate" instruction is called with r19 as a pointer. Very strange..
0
 
LVL 86

Expert Comment

by:jkr
ID: 39176468
Maybe a snippet of that code?
0
Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Author Comment

by:sctccomm
ID: 39176497
I'll start working on reducing it, but there is so much code it will probably take a couple of days.

Thanks !
0
 
LVL 32

Accepted Solution

by:
phoffric earned 1500 total points
ID: 39176547
>> I can no longer access any local (stack) variables without getting a segmentation fault
If you increased the size of an auto-array to exceed the stack size limit, you may experience the symptoms you described.
0
 

Author Closing Comment

by:sctccomm
ID: 39182141
Turns out here is a memcpy that is passed the wrong size parameter
0
 
LVL 32

Expert Comment

by:phoffric
ID: 39182365
nasty little bug.
0

Featured Post

Monthly Recap

May was a big month for new releases from Linux Academy! Take a look at what our team built recently in our blog. You can access the newest releases from our blog.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Container Orchestration platforms empower organizations to scale their apps at an exceptional rate. This is the reason numerous innovation-driven companies are moving apps to an appropriated datacenter wide platform that empowers them to scale at a …
In the first part of this tutorial we will cover the prerequisites for installing SQL Server vNext on Linux.
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
This demo shows you how to set up the containerized NetScaler CPX with NetScaler Management and Analytics System in a non-routable Mesos/Marathon environment for use with Micro-Services applications.
Suggested Courses
Course of the Month11 days, 8 hours left to enroll

752 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question