Re: getcontext() -> Bus error?
Re: getcontext() -> Bus error?
- Subject: Re: getcontext() -> Bus error?
- From: Kevin Van Vechten <email@hidden>
- Date: Thu, 31 Jan 2008 20:15:58 -0800
On Jan 31, 2008, at 7:42 PM, Anton Rang wrote:
On Jan 31, 2008, at 6:52 PM, Edd Dawson wrote:
int main(void)
{
ucontext_t ctx;
getcontext(&ctx);
return 0;
}
edd:guff developer$ gcc getcontext.c -o getcontext -W -Wall -ansi -
pedantic
edd:guff developer$ ./getcontext
Bus error
edd:guff developer$
Why the bus error? What am I doing wrong?
This is a known issue where getcontext(3) is writing past the end of
the ucontext_t struct when _XOPEN_SOURCE is not defined (rdar://problem/5578699
). As a workaround, define _XOPEN_SOURCE before including ucontext.h.
While I don't understand why you're getting a bus error (haven't
looked at the library source), the problem appears to go away if you
declare ctx as a global instead of on the stack. Perhaps
getcontext() just won't let you save context onto the stack....
The buffer overflow that wipes out the return address, causing the bus
error. By using a global, the memory corruption still occurs, but
doesn't manifest itself as a bus error with main() returning so quickly.
- Kevin
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