/*
 * ldt_gdt.c - Test cases for LDT and GDT access
 * Copyright (c) 2015 Andrew Lutomirski
 */

#define _GNU_SOURCE
#include <err.h>
#include <stdio.h>
#include <stdint.h>
#include <signal.h>
#include <setjmp.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <asm/ldt.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdbool.h>
#include <pthread.h>
#include <sched.h>
#include <linux/futex.h>
#include <sys/mman.h>
#include <asm/prctl.h>
#include <sys/prctl.h>

#define AR_ACCESSED             (1<<8)

#define AR_TYPE_RODATA          (0 * (1<<9))
#define AR_TYPE_RWDATA          (1 * (1<<9))
#define AR_TYPE_RODATA_EXPDOWN  (2 * (1<<9))
#define AR_TYPE_RWDATA_EXPDOWN  (3 * (1<<9))
#define AR_TYPE_XOCODE          (4 * (1<<9))
#define AR_TYPE_XRCODE          (5 * (1<<9))
#define AR_TYPE_XOCODE_CONF     (6 * (1<<9))
#define AR_TYPE_XRCODE_CONF     (7 * (1<<9))

#define AR_DPL3                 (3 * (1<<13))

#define AR_S                    (1 << 12)
#define AR_P                    (1 << 15)
#define AR_AVL                  (1 << 20)
#define AR_L                    (1 << 21)
#define AR_DB                   (1 << 22)
#define AR_G                    (1 << 23)

static int nerrs;

/* Points to an array of 1024 ints, each holding its own index. */
static const unsigned int *counter_page;
static struct user_desc *low_user_desc;
static struct user_desc *low_user_desc_clear;  /* Use to delete GDT entry */
static int gdt_entry_num;

static void check_invalid_segment(uint16_t index, int ldt)
{
        uint32_t has_limit = 0, has_ar = 0, limit, ar;
        uint32_t selector = (index << 3) | (ldt << 2) | 3;

        asm ("lsl %[selector], %[limit]\n\t"
             "jnz 1f\n\t"
             "movl $1, %[has_limit]\n\t"
             "1:"
             : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
             : [selector] "r" (selector));
        asm ("larl %[selector], %[ar]\n\t"
             "jnz 1f\n\t"
             "movl $1, %[has_ar]\n\t"
             "1:"
             : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
             : [selector] "r" (selector));

        if (has_limit || has_ar) {
                printf("[FAIL]\t%s entry %hu is valid but should be invalid\n",
                       (ldt ? "LDT" : "GDT"), index);
                nerrs++;
        } else {
                printf("[OK]\t%s entry %hu is invalid\n",
                       (ldt ? "LDT" : "GDT"), index);
        }
}

static void check_valid_segment(uint16_t index, int ldt,
                                uint32_t expected_ar, uint32_t expected_limit,
                                bool verbose)
{
        uint32_t has_limit = 0, has_ar = 0, limit, ar;
        uint32_t selector = (index << 3) | (ldt << 2) | 3;

        asm ("lsl %[selector], %[limit]\n\t"
             "jnz 1f\n\t"
             "movl $1, %[has_limit]\n\t"
             "1:"
             : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
             : [selector] "r" (selector));
        asm ("larl %[selector], %[ar]\n\t"
             "jnz 1f\n\t"
             "movl $1, %[has_ar]\n\t"
             "1:"
             : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
             : [selector] "r" (selector));

        if (!has_limit || !has_ar) {
                printf("[FAIL]\t%s entry %hu is invalid but should be valid\n",
                       (ldt ? "LDT" : "GDT"), index);
                nerrs++;
                return;
        }

        if (ar != expected_ar) {
                printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
                       (ldt ? "LDT" : "GDT"), index, ar, expected_ar);
                nerrs++;
        } else if (limit != expected_limit) {
                printf("[FAIL]\t%s entry %hu has limit 0x%08X but expected 0x%08X\n",
                       (ldt ? "LDT" : "GDT"), index, limit, expected_limit);
                nerrs++;
        } else if (verbose) {
                printf("[OK]\t%s entry %hu has AR 0x%08X and limit 0x%08X\n",
                       (ldt ? "LDT" : "GDT"), index, ar, limit);
        }
}

static bool install_valid_mode(const struct user_desc *desc, uint32_t ar,
                               bool oldmode)
{
        int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
                          desc, sizeof(*desc));
        if (ret < -1)
                errno = -ret;
        if (ret == 0) {
                uint32_t limit = desc->limit;
                if (desc->limit_in_pages)
                        limit = (limit << 12) + 4095;
                check_valid_segment(desc->entry_number, 1, ar, limit, true);
                return true;
        } else if (errno == ENOSYS) {
                printf("[OK]\tmodify_ldt returned -ENOSYS\n");
                return false;
        } else {
                if (desc->seg_32bit) {
                        printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
                               errno);
                        nerrs++;
                        return false;
                } else {
                        printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
                        return false;
                }
        }
}

static bool install_valid(const struct user_desc *desc, uint32_t ar)
{
        return install_valid_mode(desc, ar, false);
}

static void install_invalid(const struct user_desc *desc, bool oldmode)
{
        int ret = syscall(SYS_modify_ldt, oldmode ? 1 : 0x11,
                          desc, sizeof(*desc));
        if (ret < -1)
                errno = -ret;
        if (ret == 0) {
                check_invalid_segment(desc->entry_number, 1);
        } else if (errno == ENOSYS) {
                printf("[OK]\tmodify_ldt returned -ENOSYS\n");
        } else {
                if (desc->seg_32bit) {
                        printf("[FAIL]\tUnexpected modify_ldt failure %d\n",
                               errno);
                        nerrs++;
                } else {
                        printf("[OK]\tmodify_ldt rejected 16 bit segment\n");
                }
        }
}

static int safe_modify_ldt(int func, struct user_desc *ptr,
                           unsigned long bytecount)
{
        int ret = syscall(SYS_modify_ldt, 0x11, ptr, bytecount);
        if (ret < -1)
                errno = -ret;
        return ret;
}

static void fail_install(struct user_desc *desc)
{
        if (safe_modify_ldt(0x11, desc, sizeof(*desc)) == 0) {
                printf("[FAIL]\tmodify_ldt accepted a bad descriptor\n");
                nerrs++;
        } else if (errno == ENOSYS) {
                printf("[OK]\tmodify_ldt returned -ENOSYS\n");
        } else {
                printf("[OK]\tmodify_ldt failure %d\n", errno);
        }
}

static void do_simple_tests(void)
{
        struct user_desc desc = {
                .entry_number    = 0,
                .base_addr       = 0,
                .limit           = 10,
                .seg_32bit       = 1,
                .contents        = 2, /* Code, not conforming */
                .read_exec_only  = 0,
                .limit_in_pages  = 0,
                .seg_not_present = 0,
                .useable         = 0
        };
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);

        desc.limit_in_pages = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_P | AR_DB | AR_G);

        check_invalid_segment(1, 1);

        desc.entry_number = 2;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_P | AR_DB | AR_G);

        check_invalid_segment(1, 1);

        desc.base_addr = 0xf0000000;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_P | AR_DB | AR_G);

        desc.useable = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_P | AR_DB | AR_G | AR_AVL);

        desc.seg_not_present = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_DB | AR_G | AR_AVL);

        desc.seg_32bit = 0;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_G | AR_AVL);

        desc.seg_32bit = 1;
        desc.contents = 0;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA |
                      AR_S | AR_DB | AR_G | AR_AVL);

        desc.read_exec_only = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA |
                      AR_S | AR_DB | AR_G | AR_AVL);

        desc.contents = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA_EXPDOWN |
                      AR_S | AR_DB | AR_G | AR_AVL);

        desc.read_exec_only = 0;
        desc.limit_in_pages = 0;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA_EXPDOWN |
                      AR_S | AR_DB | AR_AVL);

        desc.contents = 3;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE_CONF |
                      AR_S | AR_DB | AR_AVL);

        desc.read_exec_only = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE_CONF |
                      AR_S | AR_DB | AR_AVL);

        desc.read_exec_only = 0;
        desc.contents = 2;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE |
                      AR_S | AR_DB | AR_AVL);

        desc.read_exec_only = 1;

#ifdef __x86_64__
        desc.lm = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
                      AR_S | AR_DB | AR_AVL);
        desc.lm = 0;
#endif

        bool entry1_okay = install_valid(&desc, AR_DPL3 | AR_TYPE_XOCODE |
                                         AR_S | AR_DB | AR_AVL);

        if (entry1_okay) {
                printf("[RUN]\tTest fork\n");
                pid_t child = fork();
                if (child == 0) {
                        nerrs = 0;
                        check_valid_segment(desc.entry_number, 1,
                                            AR_DPL3 | AR_TYPE_XOCODE |
                                            AR_S | AR_DB | AR_AVL, desc.limit,
                                            true);
                        check_invalid_segment(1, 1);
                        exit(nerrs ? 1 : 0);
                } else {
                        int status;
                        if (waitpid(child, &status, 0) != child ||
                            !WIFEXITED(status)) {
                                printf("[FAIL]\tChild died\n");
                                nerrs++;
                        } else if (WEXITSTATUS(status) != 0) {
                                printf("[FAIL]\tChild failed\n");
                                nerrs++;
                        } else {
                                printf("[OK]\tChild succeeded\n");
                        }
                }

                printf("[RUN]\tTest size\n");
                int i;
                for (i = 0; i < 8192; i++) {
                        desc.entry_number = i;
                        desc.limit = i;
                        if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
                                printf("[FAIL]\tFailed to install entry %d\n", i);
                                nerrs++;
                                break;
                        }
                }
                for (int j = 0; j < i; j++) {
                        check_valid_segment(j, 1, AR_DPL3 | AR_TYPE_XOCODE |
                                            AR_S | AR_DB | AR_AVL, j, false);
                }
                printf("[DONE]\tSize test\n");
        } else {
                printf("[SKIP]\tSkipping fork and size tests because we have no LDT\n");
        }

        /* Test entry_number too high. */
        desc.entry_number = 8192;
        fail_install(&desc);

        /* Test deletion and actions mistakeable for deletion. */
        memset(&desc, 0, sizeof(desc));
        install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P);

        desc.seg_not_present = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);

        desc.seg_not_present = 0;
        desc.read_exec_only = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S | AR_P);

        desc.read_exec_only = 0;
        desc.seg_not_present = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S);

        desc.read_exec_only = 1;
        desc.limit = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);

        desc.limit = 0;
        desc.base_addr = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RODATA | AR_S);

        desc.base_addr = 0;
        install_invalid(&desc, false);

        desc.seg_not_present = 0;
        desc.read_exec_only = 0;
        desc.seg_32bit = 1;
        install_valid(&desc, AR_DPL3 | AR_TYPE_RWDATA | AR_S | AR_P | AR_DB);
        install_invalid(&desc, true);
}

/*
 * 0: thread is idle
 * 1: thread armed
 * 2: thread should clear LDT entry 0
 * 3: thread should exit
 */
static volatile unsigned int ftx;

static void *threadproc(void *ctx)
{
        cpu_set_t cpuset;
        CPU_ZERO(&cpuset);
        CPU_SET(1, &cpuset);
        if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0)
                err(1, "sched_setaffinity to CPU 1");   /* should never fail */

        while (1) {
                syscall(SYS_futex, &ftx, FUTEX_WAIT, 0, NULL, NULL, 0);
                while (ftx != 2) {
                        if (ftx >= 3)
                                return NULL;
                }

                /* clear LDT entry 0 */
                const struct user_desc desc = {};
                if (syscall(SYS_modify_ldt, 1, &desc, sizeof(desc)) != 0)
                        err(1, "modify_ldt");

                /* If ftx == 2, set it to zero.  If ftx == 100, quit. */
                unsigned int x = -2;
                asm volatile ("lock xaddl %[x], %[ftx]" :
                              [x] "+r" (x), [ftx] "+m" (ftx));
                if (x != 2)
                        return NULL;
        }
}

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");

}

static jmp_buf jmpbuf;

static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
{
        siglongjmp(jmpbuf, 1);
}

static void do_multicpu_tests(void)
{
        cpu_set_t cpuset;
        pthread_t thread;
        int failures = 0, iters = 5, i;
        unsigned short orig_ss;

        CPU_ZERO(&cpuset);
        CPU_SET(1, &cpuset);
        if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
                printf("[SKIP]\tCannot set affinity to CPU 1\n");
                return;
        }

        CPU_ZERO(&cpuset);
        CPU_SET(0, &cpuset);
        if (sched_setaffinity(0, sizeof(cpuset), &cpuset) != 0) {
                printf("[SKIP]\tCannot set affinity to CPU 0\n");
                return;
        }

        sethandler(SIGSEGV, sigsegv, 0);
#ifdef __i386__
        /* True 32-bit kernels send SIGILL instead of SIGSEGV on IRET faults. */
        sethandler(SIGILL, sigsegv, 0);
#endif

        printf("[RUN]\tCross-CPU LDT invalidation\n");

        if (pthread_create(&thread, 0, threadproc, 0) != 0)
                err(1, "pthread_create");

        asm volatile ("mov %%ss, %0" : "=rm" (orig_ss));

        for (i = 0; i < 5; i++) {
                if (sigsetjmp(jmpbuf, 1) != 0)
                        continue;

                /* Make sure the thread is ready after the last test. */
                while (ftx != 0)
                        ;

                struct user_desc desc = {
                        .entry_number    = 0,
                        .base_addr       = 0,
                        .limit           = 0xfffff,
                        .seg_32bit       = 1,
                        .contents        = 0, /* Data */
                        .read_exec_only  = 0,
                        .limit_in_pages  = 1,
                        .seg_not_present = 0,
                        .useable         = 0
                };

                if (safe_modify_ldt(0x11, &desc, sizeof(desc)) != 0) {
                        if (errno != ENOSYS)
                                err(1, "modify_ldt");
                        printf("[SKIP]\tmodify_ldt unavailable\n");
                        break;
                }

                /* Arm the thread. */
                ftx = 1;
                syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);

                asm volatile ("mov %0, %%ss" : : "r" (0x7));

                /* Go! */
                ftx = 2;

                while (ftx != 0)
                        ;

                /*
                 * On success, modify_ldt will segfault us synchronously,
                 * and we'll escape via siglongjmp.
                 */

                failures++;
                asm volatile ("mov %0, %%ss" : : "rm" (orig_ss));
        };

        ftx = 100;  /* Kill the thread. */
        syscall(SYS_futex, &ftx, FUTEX_WAKE, 0, NULL, NULL, 0);

        if (pthread_join(thread, NULL) != 0)
                err(1, "pthread_join");

        if (failures) {
                printf("[FAIL]\t%d of %d iterations failed\n", failures, iters);
                nerrs++;
        } else {
                printf("[OK]\tAll %d iterations succeeded\n", iters);
        }
}

static int finish_exec_test(void)
{
        /*
         * In a sensible world, this would be check_invalid_segment(0, 1);
         * For better or for worse, though, the LDT is inherited across exec.
         * We can probably change this safely, but for now we test it.
         */
        check_valid_segment(0, 1,
                            AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB,
                            42, true);

        return nerrs ? 1 : 0;
}

static void do_exec_test(void)
{
        printf("[RUN]\tTest exec\n");

        struct user_desc desc = {
                .entry_number    = 0,
                .base_addr       = 0,
                .limit           = 42,
                .seg_32bit       = 1,
                .contents        = 2, /* Code, not conforming */
                .read_exec_only  = 0,
                .limit_in_pages  = 0,
                .seg_not_present = 0,
                .useable         = 0
        };
        install_valid(&desc, AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB);

        pid_t child = fork();
        if (child == 0) {
                execl("/proc/self/exe", "ldt_gdt_test_exec", NULL);
                printf("[FAIL]\tCould not exec self\n");
                exit(1);        /* exec failed */
        } else {
                int status;
                if (waitpid(child, &status, 0) != child ||
                    !WIFEXITED(status)) {
                        printf("[FAIL]\tChild died\n");
                        nerrs++;
                } else if (WEXITSTATUS(status) != 0) {
                        printf("[FAIL]\tChild failed\n");
                        nerrs++;
                } else {
                        printf("[OK]\tChild succeeded\n");
                }
        }
}

static void setup_counter_page(void)
{
        unsigned int *page = mmap(NULL, 4096, PROT_READ | PROT_WRITE,
                         MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1, 0);
        if (page == MAP_FAILED)
                err(1, "mmap");

        for (int i = 0; i < 1024; i++)
                page[i] = i;
        counter_page = page;
}

static int invoke_set_thread_area(void)
{
        int ret;
        asm volatile ("int $0x80"
                      : "=a" (ret), "+m" (low_user_desc) :
                        "a" (243), "b" (low_user_desc)
                      : "flags");
        return ret;
}

static void setup_low_user_desc(void)
{
        low_user_desc = mmap(NULL, 2 * sizeof(struct user_desc),
                             PROT_READ | PROT_WRITE,
                             MAP_ANONYMOUS | MAP_PRIVATE | MAP_32BIT, -1, 0);
        if (low_user_desc == MAP_FAILED)
                err(1, "mmap");

        low_user_desc->entry_number     = -1;
        low_user_desc->base_addr        = (unsigned long)&counter_page[1];
        low_user_desc->limit            = 0xfffff;
        low_user_desc->seg_32bit        = 1;
        low_user_desc->contents         = 0; /* Data, grow-up*/
        low_user_desc->read_exec_only   = 0;
        low_user_desc->limit_in_pages   = 1;
        low_user_desc->seg_not_present  = 0;
        low_user_desc->useable          = 0;

        if (invoke_set_thread_area() == 0) {
                gdt_entry_num = low_user_desc->entry_number;
                printf("[NOTE]\tset_thread_area is available; will use GDT index %d\n", gdt_entry_num);
        } else {
                printf("[NOTE]\tset_thread_area is unavailable\n");
        }

        low_user_desc_clear = low_user_desc + 1;
        low_user_desc_clear->entry_number = gdt_entry_num;
        low_user_desc_clear->read_exec_only = 1;
        low_user_desc_clear->seg_not_present = 1;
}

static void test_gdt_invalidation(void)
{
        if (!gdt_entry_num)
                return; /* 64-bit only system -- we can't use set_thread_area */

        unsigned short prev_sel;
        unsigned short sel;
        unsigned int eax;
        const char *result;
#ifdef __x86_64__
        unsigned long saved_base;
        unsigned long new_base;
#endif

        /* Test DS */
        invoke_set_thread_area();
        eax = 243;
        sel = (gdt_entry_num << 3) | 3;
        asm volatile ("movw %%ds, %[prev_sel]\n\t"
                      "movw %[sel], %%ds\n\t"
#ifdef __i386__
                      "pushl %%ebx\n\t"
#endif
                      "movl %[arg1], %%ebx\n\t"
                      "int $0x80\n\t"   /* Should invalidate ds */
#ifdef __i386__
                      "popl %%ebx\n\t"
#endif
                      "movw %%ds, %[sel]\n\t"
                      "movw %[prev_sel], %%ds"
                      : [prev_sel] "=&r" (prev_sel), [sel] "+r" (sel),
                        "+a" (eax)
                      : "m" (low_user_desc_clear),
                        [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
                      : "flags");

        if (sel != 0) {
                result = "FAIL";
                nerrs++;
        } else {
                result = "OK";
        }
        printf("[%s]\tInvalidate DS with set_thread_area: new DS = 0x%hx\n",
               result, sel);

        /* Test ES */
        invoke_set_thread_area();
        eax = 243;
        sel = (gdt_entry_num << 3) | 3;
        asm volatile ("movw %%es, %[prev_sel]\n\t"
                      "movw %[sel], %%es\n\t"
#ifdef __i386__
                      "pushl %%ebx\n\t"
#endif
                      "movl %[arg1], %%ebx\n\t"
                      "int $0x80\n\t"   /* Should invalidate es */
#ifdef __i386__
                      "popl %%ebx\n\t"
#endif
                      "movw %%es, %[sel]\n\t"
                      "movw %[prev_sel], %%es"
                      : [prev_sel] "=&r" (prev_sel), [sel] "+r" (sel),
                        "+a" (eax)
                      : "m" (low_user_desc_clear),
                        [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
                      : "flags");

        if (sel != 0) {
                result = "FAIL";
                nerrs++;
        } else {
                result = "OK";
        }
        printf("[%s]\tInvalidate ES with set_thread_area: new ES = 0x%hx\n",
               result, sel);

        /* Test FS */
        invoke_set_thread_area();
        eax = 243;
        sel = (gdt_entry_num << 3) | 3;
#ifdef __x86_64__
        syscall(SYS_arch_prctl, ARCH_GET_FS, &saved_base);
#endif
        asm volatile ("movw %%fs, %[prev_sel]\n\t"
                      "movw %[sel], %%fs\n\t"
#ifdef __i386__
                      "pushl %%ebx\n\t"
#endif
                      "movl %[arg1], %%ebx\n\t"
                      "int $0x80\n\t"   /* Should invalidate fs */
#ifdef __i386__
                      "popl %%ebx\n\t"
#endif
                      "movw %%fs, %[sel]\n\t"
                      : [prev_sel] "=&r" (prev_sel), [sel] "+r" (sel),
                        "+a" (eax)
                      : "m" (low_user_desc_clear),
                        [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
                      : "flags");

#ifdef __x86_64__
        syscall(SYS_arch_prctl, ARCH_GET_FS, &new_base);
#endif

        /* Restore FS/BASE for glibc */
        asm volatile ("movw %[prev_sel], %%fs" : : [prev_sel] "rm" (prev_sel));
#ifdef __x86_64__
        if (saved_base)
                syscall(SYS_arch_prctl, ARCH_SET_FS, saved_base);
#endif

        if (sel != 0) {
                result = "FAIL";
                nerrs++;
        } else {
                result = "OK";
        }
        printf("[%s]\tInvalidate FS with set_thread_area: new FS = 0x%hx\n",
               result, sel);

#ifdef __x86_64__
        if (sel == 0 && new_base != 0) {
                nerrs++;
                printf("[FAIL]\tNew FSBASE was 0x%lx\n", new_base);
        } else {
                printf("[OK]\tNew FSBASE was zero\n");
        }
#endif

        /* Test GS */
        invoke_set_thread_area();
        eax = 243;
        sel = (gdt_entry_num << 3) | 3;
#ifdef __x86_64__
        syscall(SYS_arch_prctl, ARCH_GET_GS, &saved_base);
#endif
        asm volatile ("movw %%gs, %[prev_sel]\n\t"
                      "movw %[sel], %%gs\n\t"
#ifdef __i386__
                      "pushl %%ebx\n\t"
#endif
                      "movl %[arg1], %%ebx\n\t"
                      "int $0x80\n\t"   /* Should invalidate gs */
#ifdef __i386__
                      "popl %%ebx\n\t"
#endif
                      "movw %%gs, %[sel]\n\t"
                      : [prev_sel] "=&r" (prev_sel), [sel] "+r" (sel),
                        "+a" (eax)
                      : "m" (low_user_desc_clear),
                        [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
                      : "flags");

#ifdef __x86_64__
        syscall(SYS_arch_prctl, ARCH_GET_GS, &new_base);
#endif

        /* Restore GS/BASE for glibc */
        asm volatile ("movw %[prev_sel], %%gs" : : [prev_sel] "rm" (prev_sel));
#ifdef __x86_64__
        if (saved_base)
                syscall(SYS_arch_prctl, ARCH_SET_GS, saved_base);
#endif

        if (sel != 0) {
                result = "FAIL";
                nerrs++;
        } else {
                result = "OK";
        }
        printf("[%s]\tInvalidate GS with set_thread_area: new GS = 0x%hx\n",
               result, sel);

#ifdef __x86_64__
        if (sel == 0 && new_base != 0) {
                nerrs++;
                printf("[FAIL]\tNew GSBASE was 0x%lx\n", new_base);
        } else {
                printf("[OK]\tNew GSBASE was zero\n");
        }
#endif
}

int main(int argc, char **argv)
{
        if (argc == 1 && !strcmp(argv[0], "ldt_gdt_test_exec"))
                return finish_exec_test();

        setup_counter_page();
        setup_low_user_desc();

        do_simple_tests();

        do_multicpu_tests();

        do_exec_test();

        test_gdt_invalidation();

        return nerrs ? 1 : 0;
}