// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2025 Intel Corporation
 */
#define _GNU_SOURCE

#include <err.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ucontext.h>

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

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");

        return;
}

static void sigtrap(int sig, siginfo_t *info, void *ctx_void)
{
        ucontext_t *ctx = (ucontext_t *)ctx_void;
        static unsigned int loop_count_on_same_ip;
        static unsigned long last_trap_ip;

        if (last_trap_ip == ctx->uc_mcontext.gregs[REG_IP]) {
                printf("\tTrapped at %016lx\n", last_trap_ip);

                /*
                 * If the same IP is hit more than 10 times in a row, it is
                 * _considered_ an infinite loop.
                 */
                if (++loop_count_on_same_ip > 10) {
                        printf("[FAIL]\tDetected SIGTRAP infinite loop\n");
                        exit(1);
                }

                return;
        }

        loop_count_on_same_ip = 0;
        last_trap_ip = ctx->uc_mcontext.gregs[REG_IP];
        printf("\tTrapped at %016lx\n", last_trap_ip);
}

int main(int argc, char *argv[])
{
        sethandler(SIGTRAP, sigtrap, 0);

        /*
         * Set the Trap Flag (TF) to single-step the test code, therefore to
         * trigger a SIGTRAP signal after each instruction until the TF is
         * cleared.
         *
         * Because the arithmetic flags are not significant here, the TF is
         * set by pushing 0x302 onto the stack and then popping it into the
         * flags register.
         *
         * Four instructions in the following asm code are executed with the
         * TF set, thus the SIGTRAP handler is expected to run four times.
         */
        printf("[RUN]\tSIGTRAP infinite loop detection\n");
        asm volatile(
#ifdef __x86_64__
                /*
                 * Avoid clobbering the redzone
                 *
                 * Equivalent to "sub $128, %rsp", however -128 can be encoded
                 * in a single byte immediate while 128 uses 4 bytes.
                 */
                "add $-128, %rsp\n\t"
#endif
                "push $0x302\n\t"
                "popf\n\t"
                "nop\n\t"
                "nop\n\t"
                "push $0x202\n\t"
                "popf\n\t"
#ifdef __x86_64__
                "sub $-128, %rsp\n\t"
#endif
        );

        printf("[OK]\tNo SIGTRAP infinite loop detected\n");
        return 0;
}