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75 lines
2.5 KiB
C++
75 lines
2.5 KiB
C++
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// Copyright 2017 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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#include "base/android/library_loader/anchor_functions.h"
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#include "base/logging.h"
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// asm() macros below don't compile on x86, and haven't been validated outside
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// ARM.
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#if defined(ARCH_CPU_ARMEL)
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// These functions are here to, respectively:
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// 1. Check that functions are ordered
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// 2. Delimit the start of .text
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// 3. Delimit the end of .text
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//
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// (2) and (3) require a suitably constructed orderfile, with these
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// functions at the beginning and end. (1) doesn't need to be in it.
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//
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// These functions are weird: this is due to ICF (Identical Code Folding).
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// The linker merges functions that have the same code, which would be the case
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// if these functions were empty, or simple.
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// Gold's flag --icf=safe will *not* alias functions when their address is used
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// in code, but as of November 2017, we use the default setting that
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// deduplicates function in this case as well.
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//
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// Thus these functions are made to be unique, using inline .word in assembly.
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//
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// Note that code |CheckOrderingSanity()| below will make sure that these
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// functions are not aliased, in case the toolchain becomes really clever.
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extern "C" {
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void dummy_function_to_check_ordering() {
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asm(".word 0xe19c683d");
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asm(".word 0xb3d2b56");
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}
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void dummy_function_to_anchor_text() {
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asm(".word 0xe1f8940b");
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asm(".word 0xd5190cda");
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}
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void dummy_function_at_the_end_of_text() {
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asm(".word 0x133b9613");
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asm(".word 0xdcd8c46a");
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}
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} // extern "C"
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namespace base {
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namespace android {
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const size_t kStartOfText =
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reinterpret_cast<size_t>(dummy_function_to_anchor_text);
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const size_t kEndOfText =
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reinterpret_cast<size_t>(dummy_function_at_the_end_of_text);
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void CheckOrderingSanity() {
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// The linker usually keeps the input file ordering for symbols.
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// dummy_function_to_anchor_text() should then be after
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// dummy_function_to_check_ordering() without ordering.
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// This check is thus intended to catch the lack of ordering.
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CHECK_LT(kStartOfText,
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reinterpret_cast<size_t>(&dummy_function_to_check_ordering));
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CHECK_LT(kStartOfText, kEndOfText);
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CHECK_LT(kStartOfText,
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reinterpret_cast<size_t>(&dummy_function_to_check_ordering));
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CHECK_LT(kStartOfText, reinterpret_cast<size_t>(&CheckOrderingSanity));
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CHECK_GT(kEndOfText, reinterpret_cast<size_t>(&CheckOrderingSanity));
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}
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} // namespace android
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} // namespace base
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#endif // defined(ARCH_CPU_ARMEL)
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