#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <ucontext.h>

/* copies of ucontext struct matching 6.x kernels */
/* no extra stack contents */
typedef struct k_ucontext {
        unsigned long     uc_flags;
	struct ucontext  *uc_link;
	stack_t           uc_stack;
	mcontext_t	  uc_mcontext;
	sigset_t          uc_sigmask;   /* mask last for extensibility */
} k_ucontext_t;
/* extra stack contents (fpu state, exception frame part (> 4 words) */                                        
typedef struct k_ucontextf {
        unsigned long     uc_flags;
	struct ucontext  *uc_link;
	stack_t           uc_stack;
	mcontext_t	  uc_mcontext;
	sigset_t          uc_sigmask;   /* mask last for extensibility */
	long int uc_filler[174];
} k_ucontextf_t;
                                        
int depth = 200000 /* 32768 ; 200000 */;

const unsigned long i0 = 0x91929394;
const unsigned long i1 = 0xa1a2a3a4;
const unsigned long i2 = 0xb1b2b3b4;
const unsigned long i3 = 0xc1c2c3c4;
const unsigned long i4 = 0xd1d2d3d4;
const unsigned long i5 = 0xe1e2e3e4;
const unsigned long i6 = 0xf1f2f3f4;

unsigned long o0;
unsigned long o1;
unsigned long o2;
unsigned long o3;
unsigned long o4;
unsigned long o5;
unsigned long o6;

unsigned long parent_usp, child_usp;

static void rec(void)
{
	// initialize registers
	asm(	"	move.l %0, %%a2\n" 
		"	move.l %1, %%a3\n"
		"	move.l %2, %%a4\n"
		"	move.l %3, %%a5\n"
		"	move.l %4, %%d2\n"
		"	move.l %5, %%d3\n"
		"	move.l %6, %%d4\n"
		:
		: "m" (i0), "m" (i1), "m" (i2),
		  "m" (i3), "m" (i4), "m" (i5), "m" (i6)
		: "a2", "a3", "a4", "a5", "d2", "d3", "d4"
	);

	// note current usp
	asm(	"	move.l %%sp, %0\n" 
		: "=m" (parent_usp)
		:
		: "memory" 
	);

	// maybe fork a short-lived process
	if ((depth & 0x7ff) == 0)
		if (fork() == 0) {
			// note current usp
			asm(	"	move.l %%sp, %0\n" 
				: "=m" (child_usp)
				:
				: "memory" 
			);
			exit(0);
		}

	if (--depth)
		rec();	// callee to save & restore registers

	// compare register contents
	asm(	"	move.l %%a2, %0\n" 
		"	move.l %%a3, %1\n"
		"	move.l %%a4, %2\n"
		"	move.l %%a5, %3\n"
		"	move.l %%d2, %4\n"
		"	move.l %%d3, %5\n"
		"	move.l %%d4, %6\n"
		: "=m" (o0), "=m" (o1), "=m" (o2),
		  "=m" (o3), "=m" (o4), "=m" (o5), "=m" (o6)
		:
		: "memory" /* "a2", "a3", "a4", "a5", "d2", "d3", "d4" */
	);
	if (o0 != i0 || o1 != i1 || o2 != i2 ||
	    o3 != i3 || o4 != i4 || o5 != i5 || o6 != i6)
		asm("illegal");
}

static void handler(int nevermind)
{
}
            
static void rthandler(int signo, siginfo_t *info, void *ucontext)
{
	/* use struct ucontext from libc headers */
	// ucontext_t *ctx = (ucontext_t *) ucontext;
	/* use struct ucontext from kernel source */
	k_ucontext_t *ctx = (k_ucontext_t *) ucontext;
	k_ucontextf_t *ctxf = (k_ucontextf_t *) ucontext;

	if (signo == SIGCHLD) {
		unsigned long usp, pc;
		int i;

		asm(	"	move.l %%sp, %0\n" 
			: "=m" (usp)
			:
			: "memory" 
		);
		fprintf(stderr, "parent usp  : 0x%lx\n", parent_usp);
		// fprintf(stderr, "child usp   : 0x%lx\n", child_usp);
		/* top of signal stack - using ucontext w/o uc_filler
		 * Adding filler (which will take additional exception
		 * frame contents for longer tha four word frames),
		 * top of stack may end up above parent usp! */
		fprintf(stderr, "handler tos : 0x%lx\n", usp + sizeof(struct siginfo) + sizeof(struct k_ucontext) + 24);
                if (usp + sizeof(struct siginfo) + sizeof(struct k_ucontext) + 24 > parent_usp)
                        fprintf(stderr, "handler stack overwrote usp!\n");
		fprintf(stderr, "handler usp : 0x%lx\n", usp);
		fprintf(stderr, "signal usp  : 0x%lx\n", ctxf->uc_mcontext.gregs[15]);
		fprintf(stderr, "signal pc   : 0x%lx\n", ctxf->uc_mcontext.gregs[16]);
		fprintf(stderr, "signal fmtv : 0x%lx\n", ctxf->uc_filler[54]);
		fprintf(stderr, "\n");
	}
}

int main(void)

{
	struct sigaction act;
	stack_t ss;

	ss.ss_sp = malloc(SIGSTKSZ);
	if (ss.ss_sp == NULL) {
		perror("malloc");
		exit(EXIT_FAILURE);
	}
	
	ss.ss_size = SIGSTKSZ;
	ss.ss_flags = 0;
	if (sigaltstack(&ss, NULL) == -1) {
		perror("sigaltstack");
		exit(EXIT_FAILURE);
	}
	
#ifdef USE_ALTSTACK
	fprintf(stderr, "alt sig stack: 0x%lx - 0x%lx\n", ss.ss_sp, ss.ss_sp + ss.ss_size);

	act.sa_flags = SA_ONSTACK;
	act.sa_flags |= SA_SIGINFO;
	act.sa_sigaction = rthandler;
#else
	act.sa_flags = SA_SIGINFO;
	act.sa_handler = handler;
#endif
	sigemptyset(&act.sa_mask);
	if (sigaction(SIGCHLD, &act, NULL) == -1) {
		perror("sigaction");
		exit(EXIT_FAILURE);
	}

	rec();
}