Function to mangle/demangle functions
I have previously, here, been shown that C++ functions aren't easily represented in assembly. Now I am interested in reading them one way or another because Callgrind, part of Valgrind, show them demangled while in assembly they are shown mangled.
So I would like to either mangle the Valgrind function output or demangle the assembly names of functions. Anyone ever tried something like that? I was looking at a website and found out the following:
Code to implement demangling is part of the GNU Binutils package; see libiberty/cplus-dem.c and include/demangle.h.
Has anyone ever tried somethi开发者_如何学Gong like that? I want to demangle/mangle in C.
My compiler is gcc 4.x.
Use the c++filt
command line tool to demangle the name.
Here is my C++11 implementation, derived from the following page: http://gcc.gnu.org/onlinedocs/libstdc++/manual/ext_demangling.html
#include <cxxabi.h> // needed for abi::__cxa_demangle
std::shared_ptr<char> cppDemangle(const char *abiName)
{
int status;
char *ret = abi::__cxa_demangle(abiName, 0, 0, &status);
/* NOTE: must free() the returned char when done with it! */
std::shared_ptr<char> retval;
retval.reset( (char *)ret, [](char *mem) { if (mem) free((void*)mem); } );
return retval;
}
To make the memory management easy on the returned (char *), I'm using a std::shared_ptr with a custom lambda 'deleter' function that calls free() on the returned memory. Because of this, I don't ever have to worry about deleting the memory on my own, I just use it as needed, and when the shared_ptr goes out of scope, the memory will be free'd.
Here's the macro I use to access the demangled type name as a (const char *). Note that you must have RTTI turned on to have access to 'typeid'
#define CLASS_NAME(somePointer) ((const char *) cppDemangle(typeid(*somePointer).name()).get() )
So, from within a C++ class I can say:
printf("I am inside of a %s\n",CLASS_NAME(this));
This is a slight variation on Dave's version above. This is a unique_ptr version with a little bit of checking on the return type, though it looks like you could just ignore that, but somehow that just seems unclean.
auto cppDemangle (const char *abiName)
{
//
// This function allocates and returns storage in ret
//
int status;
char *ret = abi::__cxa_demangle(abiName, 0 /* output buffer */, 0 /* length */, &status);
auto deallocator = ( [](char *mem) { if (mem) free((void*)mem); } );
if (status) {
// 0: The demangling operation succeeded.
// -1: A memory allocation failure occurred.
// -2: mangled_name is not a valid name under the C++ ABI mangling rules.
// -3: One of the arguments is invalid.
std::unique_ptr<char, decltype(deallocator) > retval(nullptr, deallocator);
return retval;
}
//
// Create a unique pointer to take ownership of the returned string so it
// is freed when that pointers goes out of scope
//
std::unique_ptr<char, decltype(deallocator) > retval(ret, deallocator);
return retval;
}
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