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tls.c

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

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

#include "sysdep/tls.h"
#include "user.h"

/* 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;
}

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