From: xcomp@arcor.de
To: linux-c-programming@vger.kernel.org
Subject: swapcontext and free memory
Date: Wed, 18 Mar 2009 19:05:51 +0100 (CET) [thread overview]
Message-ID: <18142048.1237399551641.JavaMail.ngmail@webmail17.arcor-online.net> (raw)
Hi all,
I have written a small test case which simply creates a new context, swaps to it and returns to the main function. I am allocating memory for the ucontext_t structures and the stack on which the context is executed using malloc. Because of this I also want to deallocate the memory again using free. The problem is I can't deallocate the memory after swapping back. It runs only if all three free() calls are commented out. Otherwise a segmentation fault occurs. Does swapcontext handle this on its own? Can anyone explain this behavior? I didn't find anything concerning this problem in the web.
I am running this program on Ubuntu 8.04 with the following system information: Linux ubuntu8041 2.6.24-23-generic #1 SMP i686 GNU/Linux
The test program is the following one:
---
#include <stdlib.h>
#include <stdio.h>
#include <ucontext.h>
#define STACKSIZE 4096
void thread_function() {
printf("\nthread_function was called...");
}
int main(int argc, char** argv) {
printf("\nStart");
ucontext_t *main_context, *thread_context;
main_context = (ucontext*) malloc(sizeof(ucontext));
thread_context = (ucontext*) malloc(sizeof(ucontext));
void* thread_stack = malloc(STACKSIZE);
printf("\n\nAllocated memory:\n\tmain_context:\t%p\n\tthread_context:\t%p\n\tthread_stack:\t%p", main_context, thread_context, thread_stack);
getcontext(thread_context);
thread_context->uc_stack.ss_sp = thread_stack;
thread_context->uc_stack.ss_size = sizeof(thread_stack);
thread_context->uc_stack.ss_flags = 0;
thread_context->uc_flags = 0;
thread_context->uc_link = main_context;
sigemptyset(&(thread_context->uc_sigmask));
makecontext(thread_context, thread_function, 0);
swapcontext(main_context, thread_context);
printf("\n\nswapcontext() returned. Freeing memory starts now...");
free(thread_stack);
printf("\nthread_stack was deallocated...");
free(thread_context);
printf("\nthread_context was deallocated...");
free(main_context);
printf("\nmain_context was deallocated...");
printf("\n\nEnd");
}
---
Best,
Matthias :-)
Zerreißen Sie die Netze der Phisher, Hacker und Betrüger!
Ihre Internet-Sicherheits-Seiten auf Arcor.de bieten alle Infos und Hilfsmittel, die Sie zum sicheren Surfen brauchen! Play it safe!
http://www.arcor.de/footer-sicherheit/
--
To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
next reply other threads:[~2009-03-18 18:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-18 18:05 xcomp [this message]
2009-03-18 19:22 ` swapcontext and free memory Tiago Maluta
2009-03-19 10:21 ` Jon Mayo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=18142048.1237399551641.JavaMail.ngmail@webmail17.arcor-online.net \
--to=xcomp@arcor.de \
--cc=linux-c-programming@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).