inst_prof.c

struct Template {
	int64_t data_64;
	int32_t data_32;
	int16_t data_16;
	char data_char;
} value {
	// the x'es get instructions written onto them
	// notice that those instructions are nops
	//xxxxxx
	0x90909000001000b9,
	//      xx
	0x01e98390,
	0xf775,
	0xc3
};

// the data above is actually a bunch of opcodes
// 
// .data:00000000 b9 00 10 00 00                   mov    ecx,0x1000
// .data:00000005 90                               nop    <<<< this gets filled up by the user and then executed
// .data:00000006 90                               nop    <<<< this gets filled up by the user and then executed
// .data:00000007 90                               nop    <<<< this gets filled up by the user and then executed
// .data:00000008 90                               nop    <<<< this gets filled up by the user and then executed
// .data:00000009 83 e9 01                         sub    ecx,0x1
// .data:0000000c 75 f7                            jne    0x00000005
// .data:0000000e c3                               ret    

Template* template = &value;

int64_t alloc_page() {
	return mmap(
		NULL,
		4096,
		PROT_READ | PROT_WRITE,
		MAP_ANONYMOUS | MAP_PRIVATE,
		-1,
		0
	);
}

int64_t free_page(page) {
	return munmap(page, 4096);
}

void make_page_executable(page) {
	mprotect(page, 4096, PROT_READ | PROT_EXEC);
}

int64_t read_byte() {
	char chars[16];
	chars[15] = 0;
	read(NULL, &chars[15], 1);
	return chars[15];
}

void read_n(dest, count) {
	void* end = dest + count;
	void* current = dest;
	if (count != 0) {
		do {
			current++;
			*(current-1) = read_byte();
		} while(current != end);
	}
}

void read_inst(dest) {
	read_n(dest, 4);
}

int64_t do_test() {
	long duration;
	long var_y;
	void* page = alloc_page();
	*page = *((int64_t*)(template + 0));
	*(page + 8) = *((int32_t*)(template + 8));
	*(page + 12) = *((int16_t*)(template + 12));
	*(page + 14) = *((char*)(template + 14));
	read_inst(page + 5);
	make_page_executable(page);
	time_start = timestamp();
	*page();
	time_end = timestamp();
	duration = time_end - time_start;
	write(STDOUT, &duration, 8);
	free_page(page);
}

int32_t main(int32_t argc, char** argv, char** envp) {
	write(STDOUT, "initializing prof...", 20);
	sleep(5);
	alarm(30);
	write(STDOUT, "ready\n", 6);
	do {
		dotest();
	} while(1);
}