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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <android/log.h>
#include <unistd.h>
#include <cstddef>
#include <cstdlib>
// Custom implementation of new and delete, this prevents dragging
// the libc++ implementation, which drags exception-related machine
// code that is not needed here. This helps reduce the size of the
// final binary considerably.
// These symbols are not exported, thus this does not affect the libraries that
// it will load, only the linker binary itself.
void* operator new(size_t size) {
void* ptr = ::malloc(size);
if (ptr != nullptr) {
return ptr;
}
// Don't assume it is possible to call any C library function like
// snprintf() here, since it might allocate heap memory and crash at
// runtime. Hence our fatal message does not contain the number of
// bytes requested by the allocation.
static const char kFatalMessage[] = "Out of memory!";
#ifdef __ANDROID__
__android_log_write(ANDROID_LOG_FATAL, "linker", kFatalMessage);
#else
::write(STDERR_FILENO, kFatalMessage, sizeof(kFatalMessage) - 1);
#endif
_exit(1);
#if defined(__GNUC__)
__builtin_unreachable();
#endif
// Adding a 'return nullptr' here will make the compiler error with a message
// stating that 'operator new(size_t)' is not allowed to return nullptr.
//
// Indeed, an new expression like 'new T' shall never return nullptr,
// according to the C++ specification, and an optimizing compiler will gladly
// remove any null-checks after them (something the Fuschsia team had to
// learn the hard way when writing their kernel in C++). What is meant here
// is something like:
//
// Foo* foo = new Foo(10);
// if (!foo) { <-- entire check and branch
// ... Handle out-of-memory condition. <-- removed by an optimizing
// } <-- compiler.
//
// Note that some C++ library implementations (e.g. recent libc++) recognize
// when they are compiled with -fno-exceptions and provide a simpler version
// of operator new that can return nullptr. However, it is very hard to
// guarantee at build time that this code is linked against such a version
// of the runtime. Moreoever, technically disabling exceptions is completely
// out-of-spec regarding the C++ language, and what the compiler is allowed
// to do in this case is mostly implementation-defined, so better be safe
// than sorry here.
//
// C++ provides a non-throwing new expression that can return a nullptr
// value, but it must be written as 'new (std::nothrow) T' instead of
// 'new T', and thus nobody uses this. This ends up calling
// 'operator new(size_t, const std::nothrow_t&)' which is not implemented
// here.
}
void* operator new[](size_t size) {
return operator new(size);
}
void operator delete(void* ptr) {
// The compiler-generated code already checked that |ptr != nullptr|
// so don't to it a second time.
::free(ptr);
}
void operator delete[](void* ptr) {
::free(ptr);
}
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