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ad9e674fa0
This is a prerequisite for upstreaming our LLVM patches, as our current hack forcing `-ftls-model=initial-exec` in the Clang driver is not acceptable upstream. Currently, our kernel-managed TLS implementation limits us to only having a single block of storage for all thread-local variables that's initialized at load time. This PR merely implements the dynamic TLS interface (`__tls_get_addr` and TLSDESC) on top of our static TLS infrastructure. The current model's limitations still stand: - a single static TLS block is reserved at load time, `dlopen()`-ing shared libraries that define thread-local variables might cause us to run out of space. - the initial TLS image is not changeable post-load, so `dlopen()`-ing libraries with non-zero-initialized TLS variables is not supported. The way we repurpose `ti_module` to mean "offset within static TLS block" instead of "module index" is not ABI-compliant.
27 lines
1,018 B
C++
27 lines
1,018 B
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 <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);
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}
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}
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