boost::serialization
包含这段代码 https://github.com/boostorg/serialization/blob/76df6df23ff9ad081099a0288e943535626aeb08/include/boost/serialization/void_cast.hpp#L187:
reinterpret_cast<std::ptrdiff_t>(
static_cast<Derived *>(
reinterpret_cast<Base *>(1 << 20)
)
) - (1 << 20)
其目的是计算基类和派生类之间的偏移量。这段代码没有未定义的行为吗?
我之所以这么问是因为ASAN+UBSAN抱怨。例如,这段代码
#include <iostream>
class Foo { public: virtual void foo() {} };
class Base { public: virtual void base() {} };
class Derived: public Foo, public Base {};
int main()
{
std::cout <<
(reinterpret_cast<std::ptrdiff_t>(
static_cast<Derived *>(
reinterpret_cast<Base *>(1 << 20)
)
) - (1 << 20));
}
编译为(gcc 版本 9.2.1)
g++ -fsanitize=address -fsanitize=undefined -fno-omit-frame-pointer -g main.cpp
产生这个输出
AddressSanitizer:DEADLYSIGNAL
=================================================================
==72613==ERROR: AddressSanitizer: SEGV on unknown address 0x0000000ffff8 (pc 0x0000004012d9 bp 0x7ffd5b3eecf0 sp 0x7ffd5b3eece0 T0)
==72613==The signal is caused by a READ memory access.
#0 0x4012d8 in main main.cpp:13
#1 0x7f74a90d5f42 in __libc_start_main (/lib64/libc.so.6+0x23f42)
#2 0x40112d in _start (/home/.../a.out+0x40112d)
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV main.cpp:13 in main
是误报还是这段代码确实有问题?
2019 年 12 月 9 日更新:根据 Filipp 的提议和我的实验,这段代码似乎可以工作并且不会产生任何警告:
std::aligned_storage<sizeof(Derived)>::type data;
reinterpret_cast<char*>(&data)
- reinterpret_cast<char*>(
static_cast<Base*>(
reinterpret_cast<Derived*>(&data)));
有人看到这个片段有什么问题吗?如果没有的话,我会建议boost
.
2019 年 12 月 16 日更新:修复被合并 https://github.com/boostorg/serialization/commit/489eef0e178574c9cd8f2e508da6261aea9b0093 to boost::serialization
develop
branch.