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45 lines
1.8 KiB
C
45 lines
1.8 KiB
C
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// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_
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#define BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_
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#if defined(__GNUC__)
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#include <sys/cdefs.h> // for __THROW
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#ifndef __THROW // Not a glibc system
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#ifdef _NOEXCEPT // LLVM libc++ uses noexcept instead
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#define __THROW _NOEXCEPT
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#else
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#define __THROW
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#endif // !_NOEXCEPT
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#endif
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// Shim layer symbols need to be ALWAYS exported, regardless of component build.
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//
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// If an exported symbol is linked into a DSO, it may be preempted by a
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// definition in the main executable. If this happens to an allocator symbol, it
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// will mean that the DSO will use the main executable's allocator. This is
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// normally relatively harmless -- regular allocations should all use the same
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// allocator, but if the DSO tries to hook the allocator it will not see any
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// allocations.
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//
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// However, if LLVM LTO is enabled, the compiler may inline the shim layer
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// symbols into callers. The end result is that allocator calls in DSOs may use
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// either the main executable's allocator or the DSO's allocator, depending on
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// whether the call was inlined. This is arguably a bug in LLVM caused by its
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// somewhat irregular handling of symbol interposition (see llvm.org/PR23501).
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// To work around the bug we use noinline to prevent the symbols from being
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// inlined.
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//
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// In the long run we probably want to avoid linking the allocator bits into
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// DSOs altogether. This will save a little space and stop giving DSOs the false
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// impression that they can hook the allocator.
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#define SHIM_ALWAYS_EXPORT __attribute__((visibility("default"), noinline))
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#endif // __GNUC__
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#endif // BASE_ALLOCATOR_ALLOCATOR_SHIM_INTERNALS_H_
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