#define _GNU_SOURCE

#include <stdio.h>
#include <sys/prctl.h>
#include <asm/prctl.h>
#include <sys/ucontext.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <err.h>
#include <linux/perf_event.h>
#include <sys/mman.h>
#include <sys/syscall.h>

static volatile sig_atomic_t got_sigbus = 0;

static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
		       int flags)
{
	struct sigaction sa;
	memset(&sa, 0, sizeof(sa));
	sa.sa_sigaction = handler;
	sa.sa_flags = SA_SIGINFO | flags;
	sigemptyset(&sa.sa_mask);
	if (sigaction(sig, &sa, 0))
		err(1, "sigaction");
}

#ifdef __x86_64__
# define REG_IP REG_RIP
#else
# define REG_IP REG_EIP
#endif

extern const char rdpmc_insn[];

static void sigsegv(int sig, siginfo_t *si, void *ctx_void)
{
	ucontext_t *ctx = (ucontext_t*)ctx_void;

	if (ctx->uc_mcontext.gregs[REG_IP] == (unsigned long)rdpmc_insn) {
		got_sigbus = 1;
		ctx->uc_mcontext.gregs[REG_IP] += 2;
	} else {
		raise(SIGABRT);
	}
}

__attribute__((noinline, noclone)) static void do_rdpmc(unsigned int ecx)
{
	unsigned int eax, edx;

	got_sigbus = 0;

	asm volatile ("rdpmc_insn: rdpmc" : "=a" (eax), "=d" (edx) : "c" (ecx));

	if (got_sigbus)
		return;

	printf("PMC 0x%08X: 0x%08X%08X\n", ecx, edx, eax);
}

static int perf_event_open(struct perf_event_attr *hw_event, pid_t pid,
			   int cpu, int group_fd, unsigned long flags)
{
           return syscall(__NR_perf_event_open, hw_event, pid, cpu,
                          group_fd, flags);
}

static void* map_one(void)
{
	struct perf_event_attr pe;
	int fd;

	memset(&pe, 0, sizeof(struct perf_event_attr));
	pe.type = PERF_TYPE_HARDWARE;
	pe.size = sizeof(struct perf_event_attr);
	pe.config = PERF_COUNT_HW_INSTRUCTIONS;
	pe.disabled = 0;
	pe.exclude_kernel = 1;
	pe.exclude_hv = 1;

	fd = perf_event_open(&pe, getpid(), -1, -1, 0);
	if (fd == -1)
		err(1, "perf_event_open");

	return mmap(NULL, 4096, PROT_READ, MAP_SHARED, fd, 0);
}

int main(int argc, char **argv)
{
	if (argc == 2 && !strcmp(argv[1], "try_harder")) {
		map_one();
		munmap(map_one(), 4096);
	}

	sethandler(SIGSEGV, sigsegv, 0);

	for (unsigned int i = 0; i < 4096; i++)
		do_rdpmc(i);

	for (unsigned int i = 0; i < 4096; i++)
		do_rdpmc(i | (1<<30));

	return 0;
}