setjmp/longjmp redux

hi, new to the list but i did a little reading of the archives and it seems that setjmp/longjmp cant do what i need -- switch the stack.

why do i want to do this? i am working on porting openafs which provides its own thread library (called lwp) that is implemented with setjmp/longjmp. what needs to be done in order to make this work? based on my reading it seems that ar.rnat (???) need to be saved between the context switches? i dont know much about the ia64 architecture so if someone could give me some pointers i would be grateful.

the following code works, but only under cc -g. using cc -O fails. i assume that i am getting 'lucky' using -g.

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

static int rc;
static jmp_buf env;

dump_jmp_buf(jmp_buf a)

{
    int i;
    long *ptr = (long *)a;
    for ( i=0; i < 70; i++)
        if (ptr[i] != 0) printf("(%d) 0x%lx\n",i, ptr[i]);
}

main()

{
        char *altstack;
        unsigned long *patcher;
        int stacksize = 16*1024;

        altstack = malloc(192*1024);

        printf("altstack = %p\n", altstack);
        printf("&rc = %p\n", &rc);

        rc = setjmp(env);
        printf("rc = %d\n", rc);
        if (rc = 1)
        {
                printf("return from longjmp\n");
                exit(0);
        }

        ((unsigned long *)env)[0] = (unsigned long *)(altstack + stacksize - 32);

        dump_jmp_buf(env);

        printf("about to longjmp()...\n");
        longjmp(env, 1);
}

Chas> hi, new to the list but i did a little reading of the archives Chas> and it seems that setjmp/longjmp cant do what i need -- switch Chas> the stack.

Chas> why do i want to do this? i am working on porting openafs Chas> which provides its own thread library (called lwp) that is Chas> implemented with setjmp/longjmp. what needs to be done in Chas> order to make this work? based on my reading it seems that Chas> ar.rnat (???) need to be saved between the context switches? Chas> i dont know much about the ia64 architecture so if someone Chas> could give me some pointers i would be grateful.

For synchronous context switches ("co-routines"), use makecontext()/setcontext() et al. They have been added to glibc recently. If you're not familiar with these routines, there is an example in the glibc source tree in stdlib/tst-setcontext.c. Additional usage notes can be found in in answer 4.10 of the glibc FAQ.

	--david