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f4f8f4d4e0
This is a follow up patch to the fix for bug 19329. This adds relaxed MO atomics to accesses that were previously data races but are now race conditions, and where relaxed MO is sufficient. The race conditions all follow the pattern that the write is behind the dlopen lock, but a read can happen concurrently (e.g. during tls access) without holding the lock. For slotinfo entries the read value only matters if it reads from a synchronized write in dlopen or dlclose, otherwise the related dtv entry is not valid to access so it is fine to leave it in an inconsistent state. The same applies for GL(dl_tls_max_dtv_idx) and GL(dl_tls_generation), but there the algorithm relies on the fact that the read of the last synchronized write is an increasing value. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
55 lines
1.7 KiB
C
55 lines
1.7 KiB
C
/* Thread-local storage handling in the ELF dynamic linker. x86-64 version.
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Copyright (C) 2017-2021 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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#ifdef SHARED
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/* Work around GCC PR58066, due to which __tls_get_addr may be called
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with an unaligned stack. The compat implementation is in
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tls_get_addr-compat.S. */
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# include <dl-tls.h>
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/* Define __tls_get_addr within elf/dl-tls.c under a different
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name. */
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extern __typeof__ (__tls_get_addr) ___tls_get_addr;
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# define __tls_get_addr ___tls_get_addr
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# include <elf/dl-tls.c>
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# undef __tls_get_addr
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hidden_ver (___tls_get_addr, __tls_get_addr)
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/* Only handle slow paths for __tls_get_addr. */
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attribute_hidden
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void *
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__tls_get_addr_slow (GET_ADDR_ARGS)
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{
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dtv_t *dtv = THREAD_DTV ();
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size_t gen = atomic_load_relaxed (&GL(dl_tls_generation));
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if (__glibc_unlikely (dtv[0].counter != gen))
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return update_get_addr (GET_ADDR_PARAM);
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return tls_get_addr_tail (GET_ADDR_PARAM, dtv, NULL);
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}
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#else
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/* No compatibility symbol needed. */
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# include <elf/dl-tls.c>
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#endif
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