compile with -lsigsegv

stkintro.c

#include <inttypes.h>
#include <setjmp.h>
#include <signal.h>
#include <sigsegv.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

struct bond {
    uintptr_t dof;
    uintptr_t mid;
    uintptr_t top;
};

volatile enum {
    GOING_DOWN,
    FOUND_DOF,
    GOING_UP,
    FOUND_TOP
} dir;

void *progmem = &progmem;
void *page;

static sigjmp_buf seg_buf;
#ifndef SIGSTKSZ
# define SIGSTKSZ 16384
#endif
static uint8_t sig_stk[SIGSTKSZ];

static void
_cont(void* a1, void* a2, void* a3)
{
    (void)a1;
    (void)a2;
    (void)a3;
    siglongjmp(seg_buf, 1);
}

static int
_segv(void* addr, int serious)
{
    (void)addr;
    (void)serious;
    ++dir;
    sigsegv_leave_handler(_cont, 0, 0, 0);
    return 1;
}

static void
_over(int emergency, stackoverflow_context_t scp)
{
    (void)emergency;
    (void)scp;
    ++dir;
    siglongjmp(seg_buf, 1);
}

struct bond
look(void* a)
{
    volatile uintptr_t obs;
    struct bond ret;

    ret.mid = (uintptr_t)a;
    dir = GOING_DOWN;
    while (sigsetjmp(seg_buf, 1)) {}
    for (;;) {
        switch (dir) {
        case GOING_DOWN:
            obs = *(uintptr_t*)a;
            a -= sizeof(a);
            break;
        case FOUND_DOF:
            ret.dof = (uintptr_t)a + sizeof(a);
            dir = GOING_UP;
            a = (void*)ret.mid;
        case GOING_UP:
            obs = *(uintptr_t*)a;
            a += sizeof(a);
            break;
        case FOUND_TOP:
            ret.top = (uintptr_t)a;
            return ret;
        }
    }
}

void
show(const char* nam, struct bond bod)
{
    printf("%-8s"
           " 0x%016" PRIxPTR
#ifdef SHOW_MID
           " 0x%016" PRIxPTR
#endif
           " 0x%016" PRIxPTR
           "\n"
           "%" PRIuPTR
#ifdef SHOW_MID
           " (%" PRIuPTR
           " %" PRIuPTR ")"
#endif
           "\n"
           , nam
           , bod.dof
#ifdef SHOW_MID
           , bod.mid
#endif
           , bod.top
           , bod.top - bod.dof
#ifdef SHOW_MID
           , bod.top - bod.mid
           , bod.mid - bod.dof
#endif
           );
}

#define LOOK(X) do {    \
    bod = look(X);      \
    show(#X ":", bod);  \
} while (0)

int
main(){
    void *stack;
    struct bond bod;

    sigsegv_install_handler(&_segv);
    stackoverflow_install_handler(&_over, (void*)sig_stk, SIGSTKSZ);

    page = malloc(sizeof(page));
    *(uintptr_t*)page = (uintptr_t)page;
    stack = &stack;

    LOOK(stack);
    LOOK(progmem);
    LOOK(page);
    return 0;
}