Solved

Segmentation fault accessing local variables

Posted on 2013-05-17
7
464 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
  • 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
Master Your Team's Linux and Cloud Stack

Come see why top tech companies like Mailchimp and Media Temple use Linux Academy to build their employee training programs.

 

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 500 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

Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

Question has a verified solution.

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

This article shows you how to optimize memory allocations in C++ using placement new. Applicable especially to usecases dealing with creation of large number of objects. A brief on problem: Lets take example problem for simplicity: - I have a G…
Little introduction about CP: CP is a command on linux that use to copy files and folder from one location to another location. Example usage of CP as follow: cp /myfoder /pathto/destination/folder/ cp abc.tar.gz /pathto/destination/folder/ab…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.

816 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

Need Help in Real-Time?

Connect with top rated Experts

13 Experts available now in Live!

Get 1:1 Help Now