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627f5ede70
TLS_INIT_TCB_ALIGN is not actually used. TLS_TCB_ALIGN was likely
introduced to support a configuration where the thread pointer
has not the same alignment as THREAD_SELF. Only ia64 seems to use
that, but for the stack/pointer guard, not for storing tcbhead_t.
Some ports use TLS_TCB_OFFSET and TLS_PRE_TCB_SIZE to shift
the thread pointer, potentially landing in a different residue class
modulo the alignment, but the changes should not impact that.
In general, given that TLS variables have their own alignment
requirements, having different alignment for the (unshifted) thread
pointer and struct pthread would potentially result in dynamic
offsets, leading to more complexity.
hppa had different values before: __alignof__ (tcbhead_t), which
seems to be 4, and __alignof__ (struct pthread), which was 8
(old default) and is now 32. However, it defines THREAD_SELF as:
/* Return the thread descriptor for the current thread. */
# define THREAD_SELF \
({ struct pthread *__self; \
__self = __get_cr27(); \
__self - 1; \
})
So the thread pointer points after struct pthread (hence __self - 1),
and they have to have the same alignment on hppa as well.
Similarly, on ia64, the definitions were different. We have:
# define TLS_PRE_TCB_SIZE \
(sizeof (struct pthread) \
+ (PTHREAD_STRUCT_END_PADDING < 2 * sizeof (uintptr_t) \
? ((2 * sizeof (uintptr_t) + __alignof__ (struct pthread) - 1) \
& ~(__alignof__ (struct pthread) - 1)) \
: 0))
# define THREAD_SELF \
((struct pthread *) ((char *) __thread_self - TLS_PRE_TCB_SIZE))
And TLS_PRE_TCB_SIZE is a multiple of the struct pthread alignment
(confirmed by the new _Static_assert in sysdeps/ia64/libc-tls.c).
On m68k, we have a larger gap between tcbhead_t and struct pthread.
But as far as I can tell, the port is fine with that. The definition
of TCB_OFFSET is sufficient to handle the shifted TCB scenario.
This fixes commit 23c77f6018
("nptl: Increase default TCB alignment to 32").
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
71 lines
2.4 KiB
C
71 lines
2.4 KiB
C
/* Definition for thread-local data handling. Generic version.
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Copyright (C) 2002-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* An architecture-specific version of this file has to defined a
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number of symbols:
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TCB_ALIGNMENT
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Alignment of THREAD_SELF (struct pthread *) and the thread
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pointer.
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TLS_TCB_AT_TP or TLS_DTV_AT_TP
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The presence of one of these symbols signals which variant of
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the TLS ABI is used. There are in the moment two variants
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available:
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* the thread pointer points to a thread control block
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* the thread pointer points to the dynamic thread vector
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TLS_TCB_SIZE
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This is the size of the thread control block structure. How
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this is actually defined depends on the ABI. The thread control
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block could be internal descriptor of the thread library or
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just a data structure which allows finding the DTV.
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TLS_INIT_TCB_SIZE
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Similarly, but this value is only used at startup and in the
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dynamic linker itself. There are no threads in use at that time.
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INSTALL_DTV(tcb, init_dtv)
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This macro must install the given initial DTV into the thread control
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block TCB. The normal runtime functionality must then be able to
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use the value.
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TLS_INIT_TP(tcb)
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This macro must initialize the thread pointer to enable normal TLS
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operation. The parameter is a pointer to the thread control block.
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ld.so calls this macro once.
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THREAD_DTV()
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This macro returns the address of the DTV of the current thread.
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This normally is done using the thread register which points
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to the dtv or the TCB (from which the DTV can found).
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*/
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