From b37899d34d2190ef4b454283188f22519f096048 Mon Sep 17 00:00:00 2001 From: Sergey Bugaev Date: Sun, 19 Mar 2023 18:10:07 +0300 Subject: 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 Message-Id: <20230319151017.531737-25-bugaevc@gmail.com> --- sysdeps/mach/hurd/i386/dl-tls-initialized.c | 21 ++++++++++++++ sysdeps/mach/hurd/i386/tls.h | 43 +++++++++++++++++------------ 2 files changed, 47 insertions(+), 17 deletions(-) create mode 100644 sysdeps/mach/hurd/i386/dl-tls-initialized.c (limited to 'sysdeps/mach/hurd/i386') diff --git a/sysdeps/mach/hurd/i386/dl-tls-initialized.c b/sysdeps/mach/hurd/i386/dl-tls-initialized.c new file mode 100644 index 0000000000..493ec2396c --- /dev/null +++ b/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 + . */ + +#ifndef SHARED +unsigned short __init1_desc; +#endif diff --git a/sysdeps/mach/hurd/i386/tls.h b/sysdeps/mach/hurd/i386/tls.h index 0f8dd24145..ee7b8004bc 100644 --- a/sysdeps/mach/hurd/i386/tls.h +++ b/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) { @@ -168,11 +178,10 @@ 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) -- cgit 1.4.1