08-07-2007
Where this starts getting fun is when you have exceptions or setjmp/longjmp which let you unwind the stack without returning.
Some platforms also have "structured exception handling" (OS/2,Win32) which are basically a standardised way of stack unwinding in exceptional conditions.
Some platforms (eg 32bit PA-RISC) have a bottom-up stack rather than a top-down.
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LEARN ABOUT ULTRIX
longjmp
setjmp(3) Library Functions Manual setjmp(3)
Name
setjmp, longjmp - non-local goto
Syntax
#include <setjmp.h>
int setjmp (env)
jmp_buf env;
void longjmp (env, val)
jmp_buf env;
int val;
Description
The and functions help deal with errors and interrupts encountered in a low-level subroutine of a program.
The function saves its stack environment in env (whose type, jmp_buf, is defined in the <setjmp.h> header file) for later use by It returns
the value 0.
The function restores the environment saved by the last call of with the corresponding env argument. After finishes, program execution
continues as if the corresponding call of (which must not itself have returned in the interim) had just returned the value val. The func-
tion cannot cause to return the value 0. If is invoked with a second argument of 0, returns 1. At the time of the second return from all
accessible data have values as of the time is called. However, global variables have the expected values. For example, those as of the
time of the
Examples
#include <setjmp.h>
jmp_buf env;
int i = 0;
main ()
{
void exit();
if(setjmp(env) != 0) {
(void) printf("value of i on 2nd return from setjmp: %d0, i);
exit(0);
}
(void) printf("value of i on 1st return from setjmp: %d0, i);
i = 1;
g();
/*NOTREACHED*/
}
g()
{
longjmp(env, 1);
/*NOTREACHED*/
}
If the a.out resulting from this C language code is run, the output is as follows:
value of i on 1st return from setjmp:0
value of i on 2nd return from setjmp:1
Unexpected behavior occurs if is called without a previous call to or when the last such call was in a function which has since returned.
Restrictions
The values of the registers on the second return from are register values at the time of the first call to not those of the Thus, variables
in a given function can produce unexpected results in the presence of depending on whether they are register or stack variables.
See Also
signal(2).
RISC setjmp(3)