/*
 * signal.c: Register a sigaltstack for objtool, to be able to
 *           run a signal handler on a separate stack even if
 *           the main process stack has overflown. Print out
 *           stack overflow errors when this happens.
 */
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <sys/resource.h>
#include <string.h>

#include <objtool/objtool.h>
#include <objtool/warn.h>

static unsigned long stack_limit;

static bool is_stack_overflow(void *fault_addr)
{
        unsigned long fault = (unsigned long)fault_addr;

        /* Check if fault is in the guard page just below the limit. */
        return fault < stack_limit && fault >= stack_limit - 4096;
}

static void signal_handler(int sig_num, siginfo_t *info, void *context)
{
        struct sigaction sa_dfl = {0};
        const char *sig_name;
        char msg[256];
        int msg_len;

        switch (sig_num) {
        case SIGSEGV:   sig_name = "SIGSEGV";           break;
        case SIGBUS:    sig_name = "SIGBUS";            break;
        case SIGILL:    sig_name = "SIGILL";            break;
        case SIGABRT:   sig_name = "SIGABRT";           break;
        default:        sig_name = "Unknown signal";    break;
        }

        if (is_stack_overflow(info->si_addr)) {
                msg_len = snprintf(msg, sizeof(msg),
                                   "%s: error: %s: objtool stack overflow!\n",
                                   objname, sig_name);
        } else {
                msg_len = snprintf(msg, sizeof(msg),
                                   "%s: error: %s: objtool crash!\n",
                                   objname, sig_name);
        }

        msg_len = write(STDERR_FILENO, msg, msg_len);

        /* Re-raise the signal to trigger the core dump */
        sa_dfl.sa_handler = SIG_DFL;
        sigaction(sig_num, &sa_dfl, NULL);
        raise(sig_num);
}

static int read_stack_limit(void)
{
        unsigned long stack_start, stack_end;
        struct rlimit rlim;
        char line[256];
        int ret = 0;
        FILE *fp;

        if (getrlimit(RLIMIT_STACK, &rlim)) {
                ERROR_GLIBC("getrlimit");
                return -1;
        }

        fp = fopen("/proc/self/maps", "r");
        if (!fp) {
                ERROR_GLIBC("fopen");
                return -1;
        }

        while (fgets(line, sizeof(line), fp)) {
                if (strstr(line, "[stack]")) {
                        if (sscanf(line, "%lx-%lx", &stack_start, &stack_end) != 2) {
                                ERROR_GLIBC("sscanf");
                                ret = -1;
                                goto done;
                        }
                        stack_limit = stack_end - rlim.rlim_cur;
                        goto done;
                }
        }

        ret = -1;
        ERROR("/proc/self/maps: can't find [stack]");

done:
        fclose(fp);

        return ret;
}

int init_signal_handler(void)
{
        int signals[] = {SIGSEGV, SIGBUS, SIGILL, SIGABRT};
        struct sigaction sa;
        stack_t ss;

        if (read_stack_limit())
                return -1;

        ss.ss_sp = malloc(SIGSTKSZ);
        if (!ss.ss_sp) {
                ERROR_GLIBC("malloc");
                return -1;
        }
        ss.ss_size = SIGSTKSZ;
        ss.ss_flags = 0;

        if (sigaltstack(&ss, NULL) == -1) {
                ERROR_GLIBC("sigaltstack");
                return -1;
        }

        sa.sa_sigaction = signal_handler;
        sigemptyset(&sa.sa_mask);

        sa.sa_flags = SA_ONSTACK | SA_SIGINFO;

        for (int i = 0; i < ARRAY_SIZE(signals); i++) {
                if (sigaction(signals[i], &sa, NULL) == -1) {
                        ERROR_GLIBC("sigaction");
                        return -1;
                }
        }

        return 0;
}