hurd: Only check for TLS initialization inside rtld or in static builds

When glibc is built as a shared library, TLS is always initialized by
the call of TLS_INIT_TP () macro made inside the dynamic loader, prior
to running the main program (see dl-call_tls_init_tp.h). We can take
advantage of this: we know for sure that __LIBC_NO_TLS () will evaluate
to 0 in all other cases, so let the compiler know that explicitly too.

Also, only define _hurd_tls_init () and TLS_INIT_TP () under the same
conditions (either !SHARED or inside rtld), to statically assert that
this is the case.

Other than a microoptimization, this also helps with avoiding awkward
sharing of the __libc_tls_initialized variable between ld.so and libc.so
that we would have to do otherwise -- we know for sure that no sharing
is required, simply because __libc_tls_initialized would always be set
to true inside libc.so.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230319151017.531737-25-bugaevc@gmail.com>

sysdeps/mach/hurd/Makefile

@@ -197,6 +197,10 @@ ifeq (hurd, $(subdir))
 sysdep_routines += cthreads
 endif
 
+ifeq (elf, $(subdir))
+sysdep-dl-routines += dl-tls-initialized
+endif
+
 ifeq (io, $(subdir))
 sysdep_routines += f_setlk close_nocancel close_nocancel_nostatus \
 		   fcntl_nocancel open_nocancel openat_nocancel read_nocancel \

sysdeps/mach/hurd/i386/dl-tls-initialized.c

@@ -0,0 +1,21 @@
+/* Determine whether TLS is initialized, for i386/Hurd.
+   Copyright (C) 1995-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef SHARED
+unsigned short __init1_desc;
+#endif

sysdeps/mach/hurd/i386/tls.h

@@ -69,18 +69,6 @@ _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x30,
                   |  (desc->high_word & 0xff000000));			      \
   })
 
-/* Return 1 if TLS is not initialized yet.  */
-#ifndef SHARED
-extern unsigned short __init1_desc;
-#define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds) || (gs) == __init1_desc)
-#else
-#define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds))
-#endif
-
-#define __LIBC_NO_TLS()							      \
-  ({ unsigned short ds, gs;						      \
-     asm ("movw %%ds,%w0; movw %%gs,%w1" : "=q" (ds), "=q" (gs));	      \
-     __builtin_expect(__HURD_DESC_INITIAL(gs, ds), 0); })
 #endif
 
 /* The TCB can have any size and the memory following the address the
@@ -125,6 +113,28 @@ extern unsigned short __init1_desc;
 
 # define HURD_SEL_LDT(sel) (__builtin_expect ((sel) & 4, 0))
 
+#ifndef SHARED
+extern unsigned short __init1_desc;
+# define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds) || (gs) == __init1_desc)
+#else
+# define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds))
+#endif
+
+#if !defined (SHARED) || IS_IN (rtld)
+/* Return 1 if TLS is not initialized yet.  */
+extern inline bool __attribute__ ((unused))
+__LIBC_NO_TLS (void)
+{
+  unsigned short ds, gs;
+  asm ("movw %%ds, %w0\n"
+       "movw %%gs, %w1"
+       : "=q" (ds), "=q" (gs));
+  return __glibc_unlikely (__HURD_DESC_INITIAL (gs, ds));
+}
+
+/* Code to initially initialize the thread pointer.  This might need
+   special attention since 'errno' is not yet available and if the
+   operation can cause a failure 'errno' must not be touched.  */
 static inline bool __attribute__ ((unused))
 _hurd_tls_init (tcbhead_t *tcb)
 {
@@ -173,11 +183,10 @@ out:
   return success;
 }
 
-/* Code to initially initialize the thread pointer.  This might need
-   special attention since 'errno' is not yet available and if the
-   operation can cause a failure 'errno' must not be touched.  */
-# define TLS_INIT_TP(descr) \
-    _hurd_tls_init ((tcbhead_t *) (descr))
+# define TLS_INIT_TP(descr) _hurd_tls_init ((tcbhead_t *) (descr))
+#else /* defined (SHARED) && !IS_IN (rtld) */
+# define __LIBC_NO_TLS() 0
+#endif
 
 # if __GNUC_PREREQ (6, 0)
 

sysdeps/mach/hurd/x86/init-first.c

@@ -40,13 +40,6 @@ extern char **_dl_argv;
 
 #ifndef SHARED
 static tcbhead_t __init1_tcbhead;
-# ifndef __x86_64__
-unsigned short __init1_desc;
-# endif
-#endif
-
-#ifdef __x86_64__
-unsigned char __libc_tls_initialized;
 #endif
 
 /* Things that want to be run before _hurd_init or much anything else.
@@ -166,9 +159,7 @@ first_init (void)
   _hurd_tls_init (&__init1_tcbhead);
 
   /* Make sure __LIBC_NO_TLS () keeps evaluating to 1.  */
-# ifdef __x86_64__
-  __libc_tls_initialized = 0;
-# else
+# ifndef __x86_64__
   asm ("movw %%gs,%w0" : "=m" (__init1_desc));
 # endif
 #endif

sysdeps/mach/hurd/x86_64/dl-tls-initialized.c

@@ -0,0 +1,21 @@
+/* Determine whether TLS is initialized, for x86_64/Hurd.
+   Copyright (C) 1995-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#if !defined (SHARED) || IS_IN (rtld)
+unsigned short __libc_tls_initialized;
+#endif

sysdeps/mach/hurd/x86_64/tls.h

@@ -68,10 +68,6 @@ _Static_assert (offsetof (tcbhead_t, stack_guard) == 0x28,
 _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x70,
                 "split stack pointer offset");
 
-extern unsigned char __libc_tls_initialized;
-
-# define __LIBC_NO_TLS() __builtin_expect (!__libc_tls_initialized, 0)
-
 /* The TCB can have any size and the memory following the address the
    thread pointer points to is unspecified.  Allocate the TCB there.  */
 # define TLS_TCB_AT_TP	1
@@ -87,8 +83,6 @@ extern unsigned char __libc_tls_initialized;
 # define TCB_ALIGNMENT	64
 
 
-# define TLS_INIT_TP(descr) _hurd_tls_init ((tcbhead_t *) (descr))
-
 # define THREAD_SELF							\
   (*(tcbhead_t * __seg_fs *) offsetof (tcbhead_t, tcb))
 /* Read member of the thread descriptor directly.  */
@@ -174,6 +168,10 @@ _hurd_tls_new (thread_t child, tcbhead_t *tcb)
                              i386_FSGS_BASE_STATE_COUNT);
 }
 
+# if !defined (SHARED) || IS_IN (rtld)
+extern unsigned char __libc_tls_initialized;
+#  define __LIBC_NO_TLS() __builtin_expect (!__libc_tls_initialized, 0)
+
 static inline bool __attribute__ ((unused))
 _hurd_tls_init (tcbhead_t *tcb)
 {
@@ -197,6 +195,12 @@ _hurd_tls_init (tcbhead_t *tcb)
   return err == 0;
 }
 
+#  define TLS_INIT_TP(descr) _hurd_tls_init ((tcbhead_t *) (descr))
+# else /* defined (SHARED) && !IS_IN (rtld) */
+#  define __LIBC_NO_TLS() 0
+# endif
+
+
 
 /* Global scope switch support.  */
 # define THREAD_GSCOPE_FLAG_UNUSED 0