#include "config.h"
#include <stdio.h>
#include <string.h>

/**
 *
 * altstack - run a function with a dedicated stack, and then release the memory
 *
 * C99 introduced variable length arrays to make the language easier to use
 * and more efficient. Many regard VLA's with distrust due to fear of stack
 * overflow. The same fear causes many to shy away from recursion.
 *
 * altstack seeks to liberate us from this fear. altstack creates a dedicated stack,
 * limited to a specified maximum size, runs a given function using this stack, and
 * afterwards releases the memory back to the system.
 *
 * altstack provides a way to obtain current stack usage and a way to fail gracefully.
 *
 * altstack is implemented for x86-64 only.
 *
 * Example:
 *	// allocate a VLA on a dedicated stack and show memory usage
 *	#include <assert.h>
 *	#include <err.h>
 *	#include <stdio.h>
 *	#include <stdlib.h>
 *	#include <string.h>
 *	#include <unistd.h>
 *	#include <ccan/altstack/altstack.h>
 *
 *	#define ok(x) ({ int __r = (x); if (__r == -1) err(1, #x); __r; })
 *
 *	char maps[128], rss[128];
 *
 *	static void stack_used(void) {
 *		fprintf(stderr, "stack used: %ld\n", altstack_used());
 *	}
 *
 *	static void *fn(void *arg)
 *	{
 *		ok(system(maps));
 *
 *		stack_used();
 *		ok(system(rss));
 *
 *		char p[(long) arg];
 *
 *		stack_used();
 *		ok(system(rss));
 *
 *		memset(p, 0, sizeof(p));
 *
 *		stack_used();
 *		ok(system(rss));
 *
 *		return (void *) 0xaced;
 *	}
 *
 *	int main(int argc, char *argv[])
 *	{
 *		long stk_max, vla_sz;
 *		int ret;
 *		void *out;
 *
 *		assert(argc == 3);
 *		stk_max = strtol(argv[1], NULL, 0) * 1024 * 1024;
 *		vla_sz  = strtol(argv[2], NULL, 0) * 1024 * 1024;
 *		assert(stk_max > 0 && vla_sz > 0);
 *
 *		snprintf(maps, sizeof(maps), "egrep '\\[stack' /proc/%d/maps", getpid());
 *		snprintf(rss,  sizeof(rss),  "egrep '^VmRSS' /proc/%d/status", getpid());
 *
 *		ok(system(maps));
 *		ok(system(rss));
 *
 *		ret = altstack(stk_max, fn, (void *) vla_sz, &out);
 *
 *		ok(system(maps));
 *		ok(system(rss));
 *
 *		if (ret)
 *			altstack_perror();
 *		fprintf(stderr, "altstack return: %d, fn return: %p\n", ret, out);
 *
 *		return 0;
 *	}
 *	// $ ./foo 1024 512
 *	// 7ffeb59a9000-7ffeb59ca000 rw-p 00000000 00:00 0                          [stack]
 *	// VmRSS:       760 kB
 *	// 7f9cb6005000-7f9cf6004000 rw-p 00000000 00:00 0                          [stack:25891]
 *	// stack used: 56
 *	// VmRSS:       760 kB
 *	// stack used: 536870968
 *	// VmRSS:       760 kB
 *	// stack used: 536870968
 *	// VmRSS:    525500 kB
 *	// 7ffeb59a9000-7ffeb59ca000 rw-p 00000000 00:00 0                          [stack]
 *	// VmRSS:      1332 kB
 *	// altstack return: 0, fn return: 0xaced
 *	//
 *	// $ ./foo 512 1024
 *	// 7ffd62bd0000-7ffd62bf1000 rw-p 00000000 00:00 0                          [stack]
 *	// VmRSS:       700 kB
 *	// 7f0d3bef6000-7f0d5bef5000 rw-p 00000000 00:00 0                          [stack:25900]
 *	// stack used: 56
 *	// VmRSS:       700 kB
 *	// 7ffd62bd0000-7ffd62bf1000 rw-p 00000000 00:00 0                          [stack]
 *	// VmRSS:      1336 kB
 *	// (altstack@103) SIGSEGV caught
 *	// altstack return: -1, fn return: (nil)
 *
 * Ccanlint: tests_pass_valgrind FAIL
 * License: APACHE-2
 * Author: Dan Good <dan@dancancode.com>
 */
int main(int argc, char *argv[])
{
	/* Expect exactly one argument */
	if (argc != 2)
		return 1;

	if (strcmp(argv[1], "depends") == 0)
		return 0;

	if (strcmp(argv[1], "testdepends") == 0) {
		printf("ccan/ptrint\n");
		return 0;
	}

	if (strcmp(argv[1], "ported") == 0) {
#ifdef __x86_64__
		printf("\n");
#else
		printf("Only x86-64 supported\n");
#endif
	}

	return 1;
}