setjmp and volatile local vars

A bit ago our moderator asked if simply saving local variables
to the stack across function calls in the presence of setjmp
ever got you in trouble.


The answer is of course, yes. You can longjmp from a signal
handler without having called another function.


For example:


#include <stdio.h>
#include <signal.h>
#include <setjmp.h>




jmp_buf jb;


void handlesig()
{
        longjmp(jb);
}


int main()
{
        int x = 1;
        if (setjmp(jb))
        {
printf("x = %d\n", x);
exit(0);
        }
        else
        {
signal(SIGALRM, handlesig);
alarm(1);


x = 2;
while (1)
continue;
        }
}




richard~
--------
Richard Henderson
richard@viz.tamu.edu
--

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