9437b29b43
We currently only supported Variant II which is used by x86-64. Variant I is used by both AArch64 (when using the traditional non-TLSDESC model) and RISC-V, although with small differences. The TLS layout for Variant I is essentially flipped. The static TLS blocks are after the thread pointer for Variant I, while on Variant II they are before it. Some code using ELF TLS already worked on AArch64 and RISC-V even though we only support Variant II. This is because only the local-exec model directly uses TLS offsets, other models use relocations or __tls_get_addr().
27 lines
1 KiB
C++
27 lines
1 KiB
C++
/*
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* Copyright (c) 2023, Daniel Bertalan <dani@danielbertalan.dev>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Types.h>
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#include <LibELF/Arch/tls.h>
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#include <sys/internals.h>
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extern "C" {
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// This function is called to compute the address of a thread-local variable
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// which might not be stored in the static TLS block (local-dynamic and
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// global-dynamic models). Compilers default to this when creating shared
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// libraries, as they may be loaded after program startup by `dlopen()`.
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//
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// We currently only support a static TLS block, so we take a shortcut in the
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// implementation of this interface: instead of storing the module ID in
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// ti_module, we store the module's TLS block offset. This avoids the need to
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// have a per-thread module ID -> TLS block address. This will have to be
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// changed if we support dynamically allocated TLS blocks.
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void* __tls_get_addr(__tls_index* index)
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{
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return reinterpret_cast<void*>(reinterpret_cast<FlatPtr>(__builtin_thread_pointer()) + index->ti_module + index->ti_offset + ELF::TLS_DTV_OFFSET);
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}
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}
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