1 files changed, 48 insertions, 5 deletions

diff --git a/sysdeps/mach/hurd/i386/tls.h b/sysdeps/mach/hurd/i386/tls.h
index b194a49e34..4c78685045 100644
--- a/sysdeps/mach/hurd/i386/tls.h
+++ b/sysdeps/mach/hurd/i386/tls.h
@@ -52,6 +52,15 @@ typedef struct
 #define TLS_TCB_AT_TP	1
 #define TLS_DTV_AT_TP	0
 
+/* Alignment requirement for TCB.
+
+   Some processors such as Intel Atom pay a big penalty on every
+   access using a segment override if that segment's base is not
+   aligned to the size of a cache line.  (See Intel 64 and IA-32
+   Architectures Optimization Reference Manual, section 13.3.3.3,
+   "Segment Base".)  On such machines, a cache line is 64 bytes.  */
+#define TCB_ALIGNMENT		64
+
 #ifndef __ASSEMBLER__
 
 /* Use i386-specific RPCs to arrange that %gs segment register prefix
@@ -78,6 +87,7 @@ typedef struct
       | (((unsigned int) (tcb)) & 0xff000000) /* base 24..31 */		      \
     }
 
+# define HURD_SEL_LDT(sel) (__builtin_expect((sel) & 4, 0))
 
 static inline const char * __attribute__ ((unused))
 _hurd_tls_init (tcbhead_t *tcb)
@@ -141,9 +151,40 @@ _hurd_tls_init (tcbhead_t *tcb)
 
 # include <mach/machine/thread_status.h>
 
-/* Set up TLS in the new thread of a fork child, copying from our own.  */
-static inline error_t __attribute__ ((unused))
-_hurd_tls_fork (thread_t child, struct i386_thread_state *state)
+/* Set up TLS in the new thread of a fork child, copying from the original.  */
+static inline kern_return_t __attribute__ ((unused))
+_hurd_tls_fork (thread_t child, thread_t orig, struct i386_thread_state *state)
+{
+  /* Fetch the selector set by _hurd_tls_init.  */
+  int sel;
+  asm ("mov %%gs, %w0" : "=q" (sel) : "0" (0));
+  if (sel == state->ds)		/* _hurd_tls_init was never called.  */
+    return 0;
+
+  struct descriptor desc, *_desc = &desc;
+  error_t err;
+  unsigned int count = 1;
+
+  if (HURD_SEL_LDT(sel))
+    err = __i386_get_ldt (orig, sel, 1, &_desc, &count);
+  else
+    err = __i386_get_gdt (orig, sel, &desc);
+
+  assert_perror (err);
+  if (err)
+    return err;
+
+  if (HURD_SEL_LDT(sel))
+    err = __i386_set_ldt (child, sel, &desc, 1);
+  else
+    err = __i386_set_gdt (child, &sel, desc);
+
+  state->gs = sel;
+  return err;
+}
+
+static inline kern_return_t __attribute__ ((unused))
+_hurd_tls_new (thread_t child, struct i386_thread_state *state, tcbhead_t *tcb)
 {
   /* Fetch the selector set by _hurd_tls_init.  */
   int sel;
@@ -151,11 +192,13 @@ _hurd_tls_fork (thread_t child, struct i386_thread_state *state)
   if (sel == state->ds)		/* _hurd_tls_init was never called.  */
     return 0;
 
-  tcbhead_t *const tcb = THREAD_SELF;
   HURD_TLS_DESC_DECL (desc, tcb);
   error_t err;
 
-  if (__builtin_expect (sel, 0x50) & 4) /* LDT selector */
+  tcb->tcb = tcb;
+  tcb->self = child;
+
+  if (HURD_SEL_LDT(sel))
     err = __i386_set_ldt (child, sel, &desc, 1);
   else
     err = __i386_set_gdt (child, &sel, desc);