我可以在调用纯虚函数时禁用异常吗？ [英] Can I disable exceptions for when a pure virtual function is called?

问题描述

我有一些如下所示的代码：

  class可写{b $ b public：
 virtual void putc（const char ch）= 0; 
保护：
 virtual〜Writable（）{}; 
}; 
 
类可读{
 public：
 virtual char getc（）= 0; 
保护：
 virtual〜Readable（）{}; 
}; 
  

注意两个虚函数。使用 arm-none-eabi-gcc ，并与 -fno-exceptions 产生这个输出：



  arm-none-eabi-size --format = berkeley bareCortexM.elf 
文本数据bss dec hex文件名
 108948 2304 2372 113624 1bbd8 bareCortexM.elf 
  

用方法再次运行它存根代替纯虚函数产生：



  arm-none-eabi-size --format = berkeley bareCortexM.elf 
文本数据bss十进制十六进制文件名
 47340 2296 304 49940 c314 bareCortexM.elf 
  

巨大的差异似乎是由于例外。有没有什么办法可以防止这种情况发生？

http://elegantinvention.com/blog/information/smaller-binary-size-with-c-on-baremetal-g/rel =nofollow>在baremetal（g ++）上使用C ++减小二进制大小

提供 __ cxa_pure_virtual（）实现

如果您在任何地方使用纯虚函数，但禁用了异常，您可能会
注意到您的代码再次膨胀。

这发生在我身上，并花了一段时间来追查，哎呀！

检查最终二进制文件（来自 objdump -h -C -S ）的汇编列表，它看起来像例外
正在回来！

我试过的一件事是完全链接 -nostdlib ，完全将libstdc ++拉出
图片。我提供了malloc，realloc，
免费的虚拟实现，以及其他一些我使用过的stdlib函数，但后来 avr32-g ++
抱怨我之前没有见过：我缺少
__ cxa_pure_virtual（）。

Aha ，我认为，必须是它！在
特定函数的源代码中，可以在libstdc ++中找到，是调用
std :: terminate（），在此处显示
。这次电话会在我可怜的AVR32的
闪存中抛出一个可爱的派对，在他们的路上践踏 -fno-exceptions 。

无论如何， __ cxa_pure_virtual（）是您
调用纯虚函数时实际调用的内容。像新和删除，
这可能是您想重写的东西，所以您自己的
调试/跟踪代码可以给你有用的反馈。这个实现是
的简单方法，只要确保使它 externC，这样名称就不会被损坏：

  externCvoid __cxa_pure_virtual（）{while（1）; } 
  

I have some code that looks like this:

class Writable {
public:
    virtual void putc(const char ch) = 0;
protected:
    virtual ~Writable() {};
};

class Readable {
public:
    virtual char getc() = 0;
protected:
    virtual ~Readable() {};
};

Notice the two virtual functions. Compiling this (along with my other code) using arm-none-eabi-gcc, and linking with -fno-exceptions produces this output:

arm-none-eabi-size  --format=berkeley bareCortexM.elf
   text    data     bss     dec     hex filename
 108948    2304    2372  113624   1bbd8 bareCortexM.elf

Running it again with method stubs in place of pure virtual functions yields:

arm-none-eabi-size  --format=berkeley bareCortexM.elf
   text    data     bss     dec     hex filename
  47340    2296     304   49940    c314 bareCortexM.elf

This huge difference seems to be due to exceptions. Is there any way that I can prevent this from happening?

解决方案

This is described by this blog post: Smaller binary size with C++ on baremetal (g++)

Provide a __cxa_pure_virtual() implementation

If you use pure virtual functions anywhere but have disabled exceptions, you may notice your code suddenly inflate again.

This happened to me, and it took a while to track down, whoops!
Inspecting assembly listing of the final binary (from objdump -h -C -S), it looked like exceptions were coming back!

One thing I tried was linking with -nostdlib, completely pulling libstdc++ out of the picture. I provided dummy implementations of malloc, realloc, free, and a few other stdlib functions I used, but then avr32-g++ complained about something I hadn’t seen before: I was missing __cxa_pure_virtual().

"Aha," I thought, "this has to be it!" In the source of that particular function, found in libstdc++, is a call to std::terminate(), seen here. That call threw a lovely party all over my poor AVR32′s flash memory, trampling on -fno-exceptions on their way in.

Anyway, __cxa_pure_virtual() is what actually gets called when you call a pure virtual function. Like new and delete, this is probably something you want to override anyway so your own debug/trace code can give you useful feedback. The implementation is straightforward, just be sure to make it extern "C" so the name doesn’t get mangled:

extern "C" void __cxa_pure_virtual() { while(1); }

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