c++ 异常处理（1）(三)
return _URC_FATAL_PHASE1_ERROR;
/* Unwind successful. Run the personality routine, if any. */
if (fs.personality)
{
code = (*fs.personality) (1, _UA_SEARCH_PHASE, exc->exception_class,
exc, &cur_context);
if (code == _URC_HANDLER_FOUND)
break;
else if (code != _URC_CONTINUE_UNWIND)
return _URC_FATAL_PHASE1_ERROR;
}
uw_update_context (&cur_context, &fs);
}
/* Indicate to _Unwind_Resume and associated subroutines that this
is not a forced unwind. Further, note where we found a handler. */
exc->private_1 = 0;
exc->private_2 = uw_identify_context (&cur_context);
cur_context = this_context;
code = _Unwind_RaiseException_Phase2 (exc, &cur_context);
if (code != _URC_INSTALL_CONTEXT)
return code;
uw_install_context (&this_context, &cur_context);
}
static _Unwind_Reason_Code
_Unwind_RaiseException_Phase2(struct _Unwind_Exception *exc,
struct _Unwind_Context *context)
{
_Unwind_Reason_Code code;
while (1)
{
_Unwind_FrameState fs;
int match_handler;
code = uw_frame_state_for (context, &fs);
/* Identify when we've reached the designated handler context. */
match_handler = (uw_identify_context (context) == exc->private_2
_UA_HANDLER_FRAME : 0);
if (code != _URC_NO_REASON)
/* Some error encountered. Usually the unwinder doesn't
diagnose these and merely crashes. */
return _URC_FATAL_PHASE2_ERROR;
/* Unwind successful. Run the personality routine, if any. */
if (fs.personality)
{
code = (*fs.personality) (1, _UA_CLEANUP_PHASE | match_handler,
exc->exception_class, exc, context);
if (code == _URC_INSTALL_CONTEXT)
break;
if (code != _URC_CONTINUE_UNWIND)
return _URC_FATAL_PHASE2_ERROR;
}
/* Don't let us unwind past the handler context. */
if (match_handler)
abort ();
uw_update_context (context, &fs);
}
return code;
}
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上面两个函数分别对应了unwind过程中的这两个阶段，注意其中的：
uw_init_context()
uw_frame_state_for()
uw_update_context()
这几个函数主要是用来重建函数调用现场的，它们的实现涉及到一大堆的细节，这儿先不细说，大概原理就是，对于调用链上的函数来说，它们的很大一部分上下文是可以从堆栈上恢复回来的,如ebp,esp,返回值等。编译器为了从栈上获取这些信息，它在编译代码的时候，建立了很多表项用于记录每个可以抛异常的函数的相关信息，这些信息就在重建上下文时能够指导程序怎么去搜索栈上的东西。
做点有意思的事情
说了一大堆，下面写个测试的程序简单回顾一下前面所说的关于异常处理的大概流程：
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#include
using namespace std;
void test_func3()
{
throw 3;
cout << "test func3" << endl;
}
void test_func2()
{
cout << "test func2" << endl;
try
{
test_func3();
}
catch (int)
{
cout << "catch 2" << endl;
}
}
void test_func1()
{
cout << "test func1" << endl;
try
{
test_func2();
}
catch (...)
{
cout << "catch 1" << endl;
}
}
int main()
{
test_func1();
return 0;
}
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上面的程序运行起来后，我们可以在__gxx_personality_v0 里下一个断点。
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Breakpoint 2, 0x00dd0a46 in __gxx_personality_v0 () from /usr/lib/libstdc++.so.6
(gdb) bt
#0 0x00dd0a46 in __gxx_personality_v0 () from /usr/lib/libstdc++.so.6
#1 0x00d2af2c in _Unwind_RaiseException () from /lib/libgcc_s.so.1
#2 0x00dd10e2 in __cxa_throw () from /usr/lib/l