xref: /qemu/bsd-user/main.c (revision d37853f9)

/*
 *  qemu bsd user main
 *
 *  Copyright (c) 2003-2008 Fabrice Bellard
 *  Copyright (c) 2013-14 Stacey Son
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

#include "qemu/osdep.h"
#include "qemu-common.h"
#include "qemu/units.h"
#include "qemu/accel.h"
#include "sysemu/tcg.h"
#include "qemu-version.h"
#include <machine/trap.h>

#include "qapi/error.h"
#include "qemu.h"
#include "qemu/config-file.h"
#include "qemu/error-report.h"
#include "qemu/path.h"
#include "qemu/help_option.h"
#include "qemu/module.h"
#include "exec/exec-all.h"
#include "tcg/tcg.h"
#include "qemu/timer.h"
#include "qemu/envlist.h"
#include "qemu/cutils.h"
#include "exec/log.h"
#include "trace/control.h"

int singlestep;
unsigned long mmap_min_addr;
uintptr_t guest_base;
bool have_guest_base;
unsigned long reserved_va;

static const char *interp_prefix = CONFIG_QEMU_INTERP_PREFIX;
const char *qemu_uname_release;
enum BSDType bsd_type;

/*
 * XXX: on x86 MAP_GROWSDOWN only works if ESP <= address + 32, so
 * we allocate a bigger stack. Need a better solution, for example
 * by remapping the process stack directly at the right place
 */
unsigned long x86_stack_size = 512 * 1024;

void gemu_log(const char *fmt, ...)
{
    va_list ap;

    va_start(ap, fmt);
    vfprintf(stderr, fmt, ap);
    va_end(ap);
}

#if defined(TARGET_I386)
int cpu_get_pic_interrupt(CPUX86State *env)
{
    return -1;
}
#endif

void fork_start(void)
{
}

void fork_end(int child)
{
    if (child) {
        gdbserver_fork(thread_cpu);
    }
}

#ifdef TARGET_I386
/***********************************************************/
/* CPUX86 core interface */

uint64_t cpu_get_tsc(CPUX86State *env)
{
    return cpu_get_host_ticks();
}

static void write_dt(void *ptr, unsigned long addr, unsigned long limit,
                     int flags)
{
    unsigned int e1, e2;
    uint32_t *p;
    e1 = (addr << 16) | (limit & 0xffff);
    e2 = ((addr >> 16) & 0xff) | (addr & 0xff000000) | (limit & 0x000f0000);
    e2 |= flags;
    p = ptr;
    p[0] = tswap32(e1);
    p[1] = tswap32(e2);
}

static uint64_t *idt_table;
#ifdef TARGET_X86_64
static void set_gate64(void *ptr, unsigned int type, unsigned int dpl,
                       uint64_t addr, unsigned int sel)
{
    uint32_t *p, e1, e2;
    e1 = (addr & 0xffff) | (sel << 16);
    e2 = (addr & 0xffff0000) | 0x8000 | (dpl << 13) | (type << 8);
    p = ptr;
    p[0] = tswap32(e1);
    p[1] = tswap32(e2);
    p[2] = tswap32(addr >> 32);
    p[3] = 0;
}
/* only dpl matters as we do only user space emulation */
static void set_idt(int n, unsigned int dpl)
{
    set_gate64(idt_table + n * 2, 0, dpl, 0, 0);
}
#else
static void set_gate(void *ptr, unsigned int type, unsigned int dpl,
                     uint32_t addr, unsigned int sel)
{
    uint32_t *p, e1, e2;
    e1 = (addr & 0xffff) | (sel << 16);
    e2 = (addr & 0xffff0000) | 0x8000 | (dpl << 13) | (type << 8);
    p = ptr;
    p[0] = tswap32(e1);
    p[1] = tswap32(e2);
}

/* only dpl matters as we do only user space emulation */
static void set_idt(int n, unsigned int dpl)
{
    set_gate(idt_table + n, 0, dpl, 0, 0);
}
#endif

void cpu_loop(CPUX86State *env)
{
    CPUState *cs = env_cpu(env);
    int trapnr;
    abi_ulong pc;
    /* target_siginfo_t info; */

    for (;;) {
        cpu_exec_start(cs);
        trapnr = cpu_exec(cs);
        cpu_exec_end(cs);
        process_queued_cpu_work(cs);

        switch (trapnr) {
        case 0x80:
            /* syscall from int $0x80 */
            if (bsd_type == target_freebsd) {
                abi_ulong params = (abi_ulong) env->regs[R_ESP] +
                    sizeof(int32_t);
                int32_t syscall_nr = env->regs[R_EAX];
                int32_t arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8;

                if (syscall_nr == TARGET_FREEBSD_NR_syscall) {
                    get_user_s32(syscall_nr, params);
                    params += sizeof(int32_t);
                } else if (syscall_nr == TARGET_FREEBSD_NR___syscall) {
                    get_user_s32(syscall_nr, params);
                    params += sizeof(int64_t);
                }
                get_user_s32(arg1, params);
                params += sizeof(int32_t);
                get_user_s32(arg2, params);
                params += sizeof(int32_t);
                get_user_s32(arg3, params);
                params += sizeof(int32_t);
                get_user_s32(arg4, params);
                params += sizeof(int32_t);
                get_user_s32(arg5, params);
                params += sizeof(int32_t);
                get_user_s32(arg6, params);
                params += sizeof(int32_t);
                get_user_s32(arg7, params);
                params += sizeof(int32_t);
                get_user_s32(arg8, params);
                env->regs[R_EAX] = do_freebsd_syscall(env,
                                                      syscall_nr,
                                                      arg1,
                                                      arg2,
                                                      arg3,
                                                      arg4,
                                                      arg5,
                                                      arg6,
                                                      arg7,
                                                      arg8);
            } else { /* if (bsd_type == target_openbsd) */
                env->regs[R_EAX] = do_openbsd_syscall(env,
                                                      env->regs[R_EAX],
                                                      env->regs[R_EBX],
                                                      env->regs[R_ECX],
                                                      env->regs[R_EDX],
                                                      env->regs[R_ESI],
                                                      env->regs[R_EDI],
                                                      env->regs[R_EBP]);
            }
            if (((abi_ulong)env->regs[R_EAX]) >= (abi_ulong)(-515)) {
                env->regs[R_EAX] = -env->regs[R_EAX];
                env->eflags |= CC_C;
            } else {
                env->eflags &= ~CC_C;
            }
            break;
#ifndef TARGET_ABI32
        case EXCP_SYSCALL:
            /* syscall from syscall instruction */
            if (bsd_type == target_freebsd) {
                env->regs[R_EAX] = do_freebsd_syscall(env,
                                                      env->regs[R_EAX],
                                                      env->regs[R_EDI],
                                                      env->regs[R_ESI],
                                                      env->regs[R_EDX],
                                                      env->regs[R_ECX],
                                                      env->regs[8],
                                                      env->regs[9], 0, 0);
            } else { /* if (bsd_type == target_openbsd) */
                env->regs[R_EAX] = do_openbsd_syscall(env,
                                                      env->regs[R_EAX],
                                                      env->regs[R_EDI],
                                                      env->regs[R_ESI],
                                                      env->regs[R_EDX],
                                                      env->regs[10],
                                                      env->regs[8],
                                                      env->regs[9]);
            }
            env->eip = env->exception_next_eip;
            if (((abi_ulong)env->regs[R_EAX]) >= (abi_ulong)(-515)) {
                env->regs[R_EAX] = -env->regs[R_EAX];
                env->eflags |= CC_C;
            } else {
                env->eflags &= ~CC_C;
            }
            break;
#endif
        case EXCP_INTERRUPT:
            /* just indicate that signals should be handled asap */
            break;
        default:
            pc = env->segs[R_CS].base + env->eip;
            fprintf(stderr,
                    "qemu: 0x%08lx: unhandled CPU exception 0x%x - aborting\n",
                    (long)pc, trapnr);
            abort();
        }
        process_pending_signals(env);
    }
}
#endif

static void usage(void)
{
    printf("qemu-" TARGET_NAME " version " QEMU_FULL_VERSION
           "\n" QEMU_COPYRIGHT "\n"
           "usage: qemu-" TARGET_NAME " [options] program [arguments...]\n"
           "BSD CPU emulator (compiled for %s emulation)\n"
           "\n"
           "Standard options:\n"
           "-h                print this help\n"
           "-g port           wait gdb connection to port\n"
           "-L path           set the elf interpreter prefix (default=%s)\n"
           "-s size           set the stack size in bytes (default=%ld)\n"
           "-cpu model        select CPU (-cpu help for list)\n"
           "-drop-ld-preload  drop LD_PRELOAD for target process\n"
           "-E var=value      sets/modifies targets environment variable(s)\n"
           "-U var            unsets targets environment variable(s)\n"
           "-B address        set guest_base address to address\n"
           "-bsd type         select emulated BSD type FreeBSD/NetBSD/OpenBSD (default)\n"
           "\n"
           "Debug options:\n"
           "-d item1[,...]    enable logging of specified items\n"
           "                  (use '-d help' for a list of log items)\n"
           "-D logfile        write logs to 'logfile' (default stderr)\n"
           "-p pagesize       set the host page size to 'pagesize'\n"
           "-singlestep       always run in singlestep mode\n"
           "-strace           log system calls\n"
           "-trace            [[enable=]<pattern>][,events=<file>][,file=<file>]\n"
           "                  specify tracing options\n"
           "\n"
           "Environment variables:\n"
           "QEMU_STRACE       Print system calls and arguments similar to the\n"
           "                  'strace' program.  Enable by setting to any value.\n"
           "You can use -E and -U options to set/unset environment variables\n"
           "for target process.  It is possible to provide several variables\n"
           "by repeating the option.  For example:\n"
           "    -E var1=val2 -E var2=val2 -U LD_PRELOAD -U LD_DEBUG\n"
           "Note that if you provide several changes to single variable\n"
           "last change will stay in effect.\n"
           "\n"
           QEMU_HELP_BOTTOM "\n"
           ,
           TARGET_NAME,
           interp_prefix,
           x86_stack_size);
    exit(1);
}

THREAD CPUState *thread_cpu;

bool qemu_cpu_is_self(CPUState *cpu)
{
    return thread_cpu == cpu;
}

void qemu_cpu_kick(CPUState *cpu)
{
    cpu_exit(cpu);
}

/* Assumes contents are already zeroed.  */
void init_task_state(TaskState *ts)
{
    int i;

    ts->used = 1;
    ts->first_free = ts->sigqueue_table;
    for (i = 0; i < MAX_SIGQUEUE_SIZE - 1; i++) {
        ts->sigqueue_table[i].next = &ts->sigqueue_table[i + 1];
    }
    ts->sigqueue_table[i].next = NULL;
}

int main(int argc, char **argv)
{
    const char *filename;
    const char *cpu_model;
    const char *cpu_type;
    const char *log_file = NULL;
    const char *log_mask = NULL;
    struct target_pt_regs regs1, *regs = &regs1;
    struct image_info info1, *info = &info1;
    struct bsd_binprm bprm;
    TaskState ts1, *ts = &ts1;
    CPUArchState *env;
    CPUState *cpu;
    int optind, rv;
    const char *r;
    const char *gdbstub = NULL;
    char **target_environ, **wrk;
    envlist_t *envlist = NULL;
    bsd_type = target_openbsd;

    if (argc <= 1) {
        usage();
    }

    error_init(argv[0]);
    module_call_init(MODULE_INIT_TRACE);
    qemu_init_cpu_list();
    module_call_init(MODULE_INIT_QOM);

    envlist = envlist_create();

    /* add current environment into the list */
    for (wrk = environ; *wrk != NULL; wrk++) {
        (void) envlist_setenv(envlist, *wrk);
    }

    cpu_model = NULL;

    qemu_add_opts(&qemu_trace_opts);

    optind = 1;
    for (;;) {
        if (optind >= argc) {
            break;
        }
        r = argv[optind];
        if (r[0] != '-') {
            break;
        }
        optind++;
        r++;
        if (!strcmp(r, "-")) {
            break;
        } else if (!strcmp(r, "d")) {
            if (optind >= argc) {
                break;
            }
            log_mask = argv[optind++];
        } else if (!strcmp(r, "D")) {
            if (optind >= argc) {
                break;
            }
            log_file = argv[optind++];
        } else if (!strcmp(r, "E")) {
            r = argv[optind++];
            if (envlist_setenv(envlist, r) != 0) {
                usage();
            }
        } else if (!strcmp(r, "ignore-environment")) {
            envlist_free(envlist);
            envlist = envlist_create();
        } else if (!strcmp(r, "U")) {
            r = argv[optind++];
            if (envlist_unsetenv(envlist, r) != 0) {
                usage();
            }
        } else if (!strcmp(r, "s")) {
            r = argv[optind++];
            rv = qemu_strtoul(r, &r, 0, &x86_stack_size);
            if (rv < 0 || x86_stack_size <= 0) {
                usage();
            }
            if (*r == 'M') {
                x86_stack_size *= MiB;
            } else if (*r == 'k' || *r == 'K') {
                x86_stack_size *= KiB;
            }
        } else if (!strcmp(r, "L")) {
            interp_prefix = argv[optind++];
        } else if (!strcmp(r, "p")) {
            qemu_host_page_size = atoi(argv[optind++]);
            if (qemu_host_page_size == 0 ||
                (qemu_host_page_size & (qemu_host_page_size - 1)) != 0) {
                fprintf(stderr, "page size must be a power of two\n");
                exit(1);
            }
        } else if (!strcmp(r, "g")) {
            gdbstub = g_strdup(argv[optind++]);
        } else if (!strcmp(r, "r")) {
            qemu_uname_release = argv[optind++];
        } else if (!strcmp(r, "cpu")) {
            cpu_model = argv[optind++];
            if (is_help_option(cpu_model)) {
                /* XXX: implement xxx_cpu_list for targets that still miss it */
#if defined(cpu_list)
                cpu_list();
#endif
                exit(1);
            }
        } else if (!strcmp(r, "B")) {
            rv = qemu_strtoul(argv[optind++], NULL, 0, &guest_base);
            if (rv < 0) {
                usage();
            }
            have_guest_base = true;
        } else if (!strcmp(r, "drop-ld-preload")) {
            (void) envlist_unsetenv(envlist, "LD_PRELOAD");
        } else if (!strcmp(r, "bsd")) {
            if (!strcasecmp(argv[optind], "freebsd")) {
                bsd_type = target_freebsd;
            } else if (!strcasecmp(argv[optind], "netbsd")) {
                bsd_type = target_netbsd;
            } else if (!strcasecmp(argv[optind], "openbsd")) {
                bsd_type = target_openbsd;
            } else {
                usage();
            }
            optind++;
        } else if (!strcmp(r, "singlestep")) {
            singlestep = 1;
        } else if (!strcmp(r, "strace")) {
            do_strace = 1;
        } else if (!strcmp(r, "trace")) {
            trace_opt_parse(optarg);
        } else {
            usage();
        }
    }

    /* init debug */
    qemu_log_needs_buffers();
    qemu_set_log_filename(log_file, &error_fatal);
    if (log_mask) {
        int mask;

        mask = qemu_str_to_log_mask(log_mask);
        if (!mask) {
            qemu_print_log_usage(stdout);
            exit(1);
        }
        qemu_set_log(mask);
    }

    if (optind >= argc) {
        usage();
    }
    filename = argv[optind];

    if (!trace_init_backends()) {
        exit(1);
    }
    trace_init_file();

    /* Zero out regs */
    memset(regs, 0, sizeof(struct target_pt_regs));

    /* Zero bsd params */
    memset(&bprm, 0, sizeof(bprm));

    /* Zero out image_info */
    memset(info, 0, sizeof(struct image_info));

    /* Scan interp_prefix dir for replacement files. */
    init_paths(interp_prefix);

    if (cpu_model == NULL) {
#if defined(TARGET_I386)
#ifdef TARGET_X86_64
        cpu_model = "qemu64";
#else
        cpu_model = "qemu32";
#endif
#else
        cpu_model = "any";
#endif
    }

    cpu_type = parse_cpu_option(cpu_model);
    /* init tcg before creating CPUs and to get qemu_host_page_size */
    {
        AccelClass *ac = ACCEL_GET_CLASS(current_accel());

        accel_init_interfaces(ac);
        ac->init_machine(NULL);
    }
    cpu = cpu_create(cpu_type);
    env = cpu->env_ptr;
    cpu_reset(cpu);
    thread_cpu = cpu;

    if (getenv("QEMU_STRACE")) {
        do_strace = 1;
    }

    target_environ = envlist_to_environ(envlist, NULL);
    envlist_free(envlist);

    /*
     * Now that page sizes are configured we can do
     * proper page alignment for guest_base.
     */
    guest_base = HOST_PAGE_ALIGN(guest_base);

    /*
     * Read in mmap_min_addr kernel parameter.  This value is used
     * When loading the ELF image to determine whether guest_base
     * is needed.
     *
     * When user has explicitly set the quest base, we skip this
     * test.
     */
    if (!have_guest_base) {
        FILE *fp;

        fp = fopen("/proc/sys/vm/mmap_min_addr", "r");
        if (fp != NULL) {
            unsigned long tmp;
            if (fscanf(fp, "%lu", &tmp) == 1) {
                mmap_min_addr = tmp;
                qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%lx\n",
                              mmap_min_addr);
            }
            fclose(fp);
        }
    }

    if (loader_exec(filename, argv + optind, target_environ, regs, info,
                    &bprm) != 0) {
        printf("Error loading %s\n", filename);
        _exit(1);
    }

    for (wrk = target_environ; *wrk; wrk++) {
        g_free(*wrk);
    }

    g_free(target_environ);

    if (qemu_loglevel_mask(CPU_LOG_PAGE)) {
        qemu_log("guest_base  %p\n", (void *)guest_base);
        log_page_dump("binary load");

        qemu_log("start_brk   0x" TARGET_ABI_FMT_lx "\n", info->start_brk);
        qemu_log("end_code    0x" TARGET_ABI_FMT_lx "\n", info->end_code);
        qemu_log("start_code  0x" TARGET_ABI_FMT_lx "\n",
                 info->start_code);
        qemu_log("start_data  0x" TARGET_ABI_FMT_lx "\n",
                 info->start_data);
        qemu_log("end_data    0x" TARGET_ABI_FMT_lx "\n", info->end_data);
        qemu_log("start_stack 0x" TARGET_ABI_FMT_lx "\n",
                 info->start_stack);
        qemu_log("brk         0x" TARGET_ABI_FMT_lx "\n", info->brk);
        qemu_log("entry       0x" TARGET_ABI_FMT_lx "\n", info->entry);
    }

    target_set_brk(info->brk);
    syscall_init();
    signal_init();

    /*
     * Now that we've loaded the binary, GUEST_BASE is fixed.  Delay
     * generating the prologue until now so that the prologue can take
     * the real value of GUEST_BASE into account.
     */
    tcg_prologue_init(tcg_ctx);

    /* build Task State */
    memset(ts, 0, sizeof(TaskState));
    init_task_state(ts);
    ts->info = info;
    cpu->opaque = ts;

#if defined(TARGET_I386)
    env->cr[0] = CR0_PG_MASK | CR0_WP_MASK | CR0_PE_MASK;
    env->hflags |= HF_PE_MASK | HF_CPL_MASK;
    if (env->features[FEAT_1_EDX] & CPUID_SSE) {
        env->cr[4] |= CR4_OSFXSR_MASK;
        env->hflags |= HF_OSFXSR_MASK;
    }
#ifndef TARGET_ABI32
    /* enable 64 bit mode if possible */
    if (!(env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM)) {
        fprintf(stderr, "The selected x86 CPU does not support 64 bit mode\n");
        exit(1);
    }
    env->cr[4] |= CR4_PAE_MASK;
    env->efer |= MSR_EFER_LMA | MSR_EFER_LME;
    env->hflags |= HF_LMA_MASK;
#endif

    /* flags setup : we activate the IRQs by default as in user mode */
    env->eflags |= IF_MASK;

    /* linux register setup */
#ifndef TARGET_ABI32
    env->regs[R_EAX] = regs->rax;
    env->regs[R_EBX] = regs->rbx;
    env->regs[R_ECX] = regs->rcx;
    env->regs[R_EDX] = regs->rdx;
    env->regs[R_ESI] = regs->rsi;
    env->regs[R_EDI] = regs->rdi;
    env->regs[R_EBP] = regs->rbp;
    env->regs[R_ESP] = regs->rsp;
    env->eip = regs->rip;
#else
    env->regs[R_EAX] = regs->eax;
    env->regs[R_EBX] = regs->ebx;
    env->regs[R_ECX] = regs->ecx;
    env->regs[R_EDX] = regs->edx;
    env->regs[R_ESI] = regs->esi;
    env->regs[R_EDI] = regs->edi;
    env->regs[R_EBP] = regs->ebp;
    env->regs[R_ESP] = regs->esp;
    env->eip = regs->eip;
#endif

    /* linux interrupt setup */
#ifndef TARGET_ABI32
    env->idt.limit = 511;
#else
    env->idt.limit = 255;
#endif
    env->idt.base = target_mmap(0, sizeof(uint64_t) * (env->idt.limit + 1),
                                PROT_READ | PROT_WRITE,
                                MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
    idt_table = g2h_untagged(env->idt.base);
    set_idt(0, 0);
    set_idt(1, 0);
    set_idt(2, 0);
    set_idt(3, 3);
    set_idt(4, 3);
    set_idt(5, 0);
    set_idt(6, 0);
    set_idt(7, 0);
    set_idt(8, 0);
    set_idt(9, 0);
    set_idt(10, 0);
    set_idt(11, 0);
    set_idt(12, 0);
    set_idt(13, 0);
    set_idt(14, 0);
    set_idt(15, 0);
    set_idt(16, 0);
    set_idt(17, 0);
    set_idt(18, 0);
    set_idt(19, 0);
    set_idt(0x80, 3);

    /* linux segment setup */
    {
        uint64_t *gdt_table;
        env->gdt.base = target_mmap(0, sizeof(uint64_t) * TARGET_GDT_ENTRIES,
                                    PROT_READ | PROT_WRITE,
                                    MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
        env->gdt.limit = sizeof(uint64_t) * TARGET_GDT_ENTRIES - 1;
        gdt_table = g2h_untagged(env->gdt.base);
#ifdef TARGET_ABI32
        write_dt(&gdt_table[__USER_CS >> 3], 0, 0xfffff,
                 DESC_G_MASK | DESC_B_MASK | DESC_P_MASK | DESC_S_MASK |
                 (3 << DESC_DPL_SHIFT) | (0xa << DESC_TYPE_SHIFT));
#else
        /* 64 bit code segment */
        write_dt(&gdt_table[__USER_CS >> 3], 0, 0xfffff,
                 DESC_G_MASK | DESC_B_MASK | DESC_P_MASK | DESC_S_MASK |
                 DESC_L_MASK |
                 (3 << DESC_DPL_SHIFT) | (0xa << DESC_TYPE_SHIFT));
#endif
        write_dt(&gdt_table[__USER_DS >> 3], 0, 0xfffff,
                 DESC_G_MASK | DESC_B_MASK | DESC_P_MASK | DESC_S_MASK |
                 (3 << DESC_DPL_SHIFT) | (0x2 << DESC_TYPE_SHIFT));
    }

    cpu_x86_load_seg(env, R_CS, __USER_CS);
    cpu_x86_load_seg(env, R_SS, __USER_DS);
#ifdef TARGET_ABI32
    cpu_x86_load_seg(env, R_DS, __USER_DS);
    cpu_x86_load_seg(env, R_ES, __USER_DS);
    cpu_x86_load_seg(env, R_FS, __USER_DS);
    cpu_x86_load_seg(env, R_GS, __USER_DS);
    /* This hack makes Wine work... */
    env->segs[R_FS].selector = 0;
#else
    cpu_x86_load_seg(env, R_DS, 0);
    cpu_x86_load_seg(env, R_ES, 0);
    cpu_x86_load_seg(env, R_FS, 0);
    cpu_x86_load_seg(env, R_GS, 0);
#endif
#else
#error unsupported target CPU
#endif

    if (gdbstub) {
        gdbserver_start(gdbstub);
        gdb_handlesig(cpu, 0);
    }
    cpu_loop(env);
    /* never exits */
    return 0;
}