uddt_fasttrap_sprint

main.c

//usr/bin/true && clang $0 && exec ./a.out
//usr/bin/true && exit 1

/* This program demonstrates how to dynamically create DTrace probes with
 * fasttrap. It currently works on Mac x86(_64) but can be easily adapted
 * to other platforms.
 *
 * Quickstart:
 * To see it work, just execute it (that magic at the top will compile and
 * run it). It will dynamically create a probe and print its probe
 * specification. Then just trace it with `dtrace(1M)`. You'll see that it
 * detects when the probe is enabled.
 */

#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <err.h>

#include <sys/fasttrap.h>

#define PAGE_SIZE 4096

void *get_rwx_page(void)
{
	void *ret;
	if ((ret = mmap(NULL, PAGE_SIZE, PROT_READ|PROT_WRITE|PROT_EXEC,
			MAP_ANON|MAP_PRIVATE, -1, 0)) == NULL) {
		err(1, "mmap");
	}
	return ret;
}

int main()
{
	int fd;
	void *execmem;
	uint8_t *execmem_bytes;

	if ((fd = open("/dev/fasttrap", O_RDWR)) < 0) {
		err(1, "open");
	}

	execmem_bytes = execmem = get_rwx_page();

	/* fill with RET */
	memset(execmem, 0xC3, PAGE_SIZE);

	/* create the fasttrap probe */
	fasttrap_probe_spec_t probe;
	probe.ftps_pid = getpid();

	/* These two are Mac-specific. Just ftps_type = DTFTP_OFFSETS on
	 * Solaris */
	probe.ftps_provider_type = DTFTP_PROVIDER_PID;
	probe.ftps_probe_type = DTFTP_OFFSETS;

	/* Just dummy names for now. */
	const char *funcname = "testfunc";
	const char *modname = "testmod";

	strcpy((char*)&probe.ftps_func, funcname);
	strcpy((char*)&probe.ftps_mod, modname);

	probe.ftps_pc = (uintptr_t)execmem;
	probe.ftps_size = 1; /* just the RET */
	probe.ftps_noffs = 1;
	probe.ftps_offs[0] = 0; /* offset 0; i.e., just that instruction */

	if (ioctl(fd, FASTTRAPIOC_MAKEPROBE, &probe) < 0)
		err(1, "ioctl FASTTRAPIOC_MAKEPROBE");
	printf("Created probe 'pid%d:%s:%s:0'\n", (int)getpid(), modname, funcname);

	/* just repeatedly fire our probe */
	for (;;) {
		usleep(500 * 1000); /* don't spin too fast */
		/* trigger dynamically created function */
		(*(void (*)(void))execmem)();
		/* TODO: could use FASTTRAP_INSTR instead of hardcoding
		 * 0xCC, but whatevs */
		/* If instr is the INT3 trap instruction */
		if (execmem_bytes[0] == 0xCC)
			printf("Probe is enabled\n");
	}

	return 0;
}