Question

当我尝试编译以下程序时

#include <iostream>
#include <memory>
#include <thread>
#include <vector>

// This function will be called from a thread 
void call_from_thread()
{
   std::cout << "Threaded: Hello, World" << std::endl;
}

int main()
{
   std::cout << "Hello World" << std::endl;

   std::thread t1(call_from_thread);
   t1.join();

   std::cout << "Goodbye World" << std::endl;
}

通过此次通话

pi @ raspberrypi：/ tmp $ arm-linux-gnueabihf-g ++ -g -Wall -O0 -ggdb -Wl，-z，nocopyreloc segfault_check.cpp -o segv_test -lpthread

它将在没有警告的情况下编译。在这种情况下，目标机器是运行rapbian stretch和gcc 6.3.0的覆盆子计算模块3。尝试运行它将导致在到达主要入口点之前立即发生段错误。

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Reading symbols from segv_test...done.
(gdb) run
Starting program: /tmp/segv_test 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x00000000 in ?? ()
(gdb) bt
#0  0x00000000 in ?? ()
#1  0x76e99148 in __dynamic_cast () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6
#2  0x76f105f4 in bool std::has_facet<std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > > >(std::locale const&) () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6
#3  0x76f02f94 in std::basic_ios<char, std::char_traits<char> >::_M_cache_locale(std::locale const&) () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6
#4  0x76f030c0 in std::basic_ios<char, std::char_traits<char> >::init(std::basic_streambuf<char, std::char_traits<char> >*) () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6
#5  0x76eab684 in std::ios_base::Init::Init() () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6
#6  0x00010de8 in __static_initialization_and_destruction_0 (__initialize_p=1, __priority=65535) at /usr/include/c++/6/iostream:74
#7  0x00010e28 in _GLOBAL__sub_I__Z16call_from_threadv () at segfault_check.cpp:44
#8  0x00011db4 in __libc_csu_init ()
#9  0x76c5460c in __libc_start_main (main=0x7efff214, argc=1993838592, argv=0x76c5460c <__libc_start_main+168>, init=0x11d68 <__libc_csu_init>, fini=0x11dc8 <__libc_csu_fini>, rtld_fini=0x76fdf9b8 <_dl_fini>, stack_end=0x7efff214)
    at libc-start.c:247
#10 0x00010a78 in _start ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
(gdb)

但是，如果我放弃nocopyreloc指令，一切似乎都有效：

pi @ raspberrypi：/ tmp $ arm-linux-gnueabihf-g ++ -g -Wall -O0 -ggdb segfault_check.cpp -o segv_test -lpthread

pi@raspberrypi:/tmp $ ./segv_test 
Hello World
Threaded: Hello, World
Goodbye World

直到今天我还不知道nocopyreloc选项。它通过我们用于交叉编译的CMake ~~默认CMAKE_EXE_LINKER_FLAGS设置~~工具链文件滑入。 binutils documentation州：

nocopyreloc禁用副本重定位的生成。

并没有解释太多。

当我使用g ++ 7.2.0在我的开发机器（linux x86_64）上编译程序时，我收到以下错误消息

./segv_test: Symbol `_ZSt4cout' causes overflow in R_X86_64_PC32 relocation
./segv_test: Symbol `_ZSt4cout' causes overflow in R_X86_64_PC32 relocation
./segv_test: Symbol `_ZSt4cout' causes overflow in R_X86_64_PC32 relocation
./segv_test: Symbol `_ZTVNSt6thread6_StateE' causes overflow in R_X86_64_PC32 relocation
Segmentation fault (core dumped)

这似乎暗示了问题的原因。显然，装载机不能进行必要的重新安置，但我不能很好地理解过程的细节。

我想知道我是否可以安全地删除nocopyreloc选项，或者我是否需要以不同方式或两者同时构建我的库？或者什么？

Answer 1

nocopyreloc是为i386 abi设计的，其中动态库中的重定位也作为重定位复制到了主要可执行文件中。当时，这是唯一的这样做。复制重定位根本没有用，在极端情况下会引起问题。标志nocopyrelocs禁止此行为。我不确定它在非i386 abis上正在做什么，但是删除此标志似乎很安全。

g ++ -Wl，-z，nocopyreloc重定位错误

1 个答案: