tls.c

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#include <errno.h>
#include <linux/unistd.h>

#include <sys/ptrace.h>
#include <sys/syscall.h>
#include <unistd.h>

#include <sysdep/tls.h>

#ifndef PTRACE_GET_THREAD_AREA
#define PTRACE_GET_THREAD_AREA 25
#endif

#ifndef PTRACE_SET_THREAD_AREA
#define PTRACE_SET_THREAD_AREA 26
#endif

/* Checks whether host supports TLS, and sets *tls_min according to the value
 * valid on the host.
 * i386 host have it == 6; x86_64 host have it == 12, for i386 emulation. */
void check_host_supports_tls(int *supports_tls, int *tls_min)
{
    /* Values for x86 and x86_64.*/
    int val[] = {GDT_ENTRY_TLS_MIN_I386, GDT_ENTRY_TLS_MIN_X86_64};
    int i;

    for (i = 0; i < ARRAY_SIZE(val); i++) {
        user_desc_t info;
        info.entry_number = val[i];

        if (syscall(__NR_get_thread_area, &info) == 0) {
            *tls_min = val[i];
            *supports_tls = 1;
            return;
        } else {
            if (errno == EINVAL)
                continue;
            else if (errno == ENOSYS)
                *supports_tls = 0;
                return;
        }
    }

    *supports_tls = 0;
}

int os_set_thread_area(user_desc_t *info, int pid)
{
    int ret;

    ret = ptrace(PTRACE_SET_THREAD_AREA, pid, info->entry_number,
             (unsigned long) info);
    if (ret < 0)
        ret = -errno;
    return ret;
}

int os_get_thread_area(user_desc_t *info, int pid)
{
    int ret;

    ret = ptrace(PTRACE_GET_THREAD_AREA, pid, info->entry_number,
             (unsigned long) info);
    if (ret < 0)
        ret = -errno;
    return ret;
}