pjs/xpcom/base/nsTypeInfo.cpp

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/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* The contents of this file are subject to the Mozilla Public
* License Version 1.1 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS
* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express oqr
* implied. See the License for the specific language governing
* rights and limitations under the License.
*
* The Original Code is nsTypeInfo.cpp code, released
* November 27, 2000.
*
* The Initial Developer of the Original Code is Netscape
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 2000 Netscape Communications Corporation. All
* Rights Reserved.
*
* Contributor(s):
* Patrick C. Beard <beard@netscape.com>
* Chris Waterson <waterson@netscape.com>
*
* Alternatively, the contents of this file may be used under the
* terms of the GNU Public License (the "GPL"), in which case the
* provisions of the GPL are applicable instead of those above.
* If you wish to allow use of your version of this file only
* under the terms of the GPL and not to allow others to use your
* version of this file under the MPL, indicate your decision by
* deleting the provisions above and replace them with the notice
* and other provisions required by the GPL. If you do not delete
* the provisions above, a recipient may use your version of this
* file under either the MPL or the GPL.
*/
/*
typeinfo.cpp
Speculatively use RTTI on a random object. If it contains a pointer at offset 0
that is in the current process' address space, and that so on, then attempt to
use C++ RTTI's typeid operation to obtain the name of the type.
by Patrick C. Beard.
*/
#include <typeinfo>
#include <ctype.h>
extern "C" const char* nsGetTypeName(void* ptr);
class IUnknown {
public:
virtual long QueryInterface() = 0;
virtual long AddRef() = 0;
virtual long Release() = 0;
};
#if defined(MACOS)
#include <Processes.h>
class AddressSpace {
public:
AddressSpace();
Boolean contains(void* ptr);
private:
ProcessInfoRec mInfo;
};
AddressSpace::AddressSpace()
{
ProcessSerialNumber psn = { 0, kCurrentProcess };
mInfo.processInfoLength = sizeof(mInfo);
::GetProcessInformation(&psn, &mInfo);
}
Boolean AddressSpace::contains(void* ptr)
{
UInt32 start = UInt32(mInfo.processLocation);
return (UInt32(ptr) >= start && UInt32(ptr) < (start + mInfo.processSize));
}
const char* nsGetTypeName(void* ptr)
{
// construct only one of these per process.
static AddressSpace space;
// sanity check the vtable pointer, before trying to use RTTI on the object.
void** vt = *(void***)ptr;
if (vt && !(unsigned(vt) & 0x3) && space.contains(vt) && space.contains(*vt)) {
IUnknown* u = static_cast<IUnknown*>(ptr);
const char* type = typeid(*u).name();
// make sure it looks like a C++ identifier.
if (type && (isalnum(type[0]) || type[0] == '_'))
return type;
}
return "void*";
}
#endif
#if defined(linux)
#include <signal.h>
#include <setjmp.h>
static jmp_buf context;
static void handler(int signum)
{
longjmp(context, signum);
}
#define attempt() setjmp(context)
class Signaller {
public:
Signaller(int signum);
~Signaller();
private:
typedef void (*handler_t) (int signum);
int mSignal;
handler_t mOldHandler;
};
Signaller::Signaller(int signum)
: mSignal(signum), mOldHandler(signal(signum, &handler))
{
}
Signaller::~Signaller()
{
signal(mSignal, mOldHandler);
}
// The following are pointers that bamboozle our otherwise feeble
// attempts to "safely" collect type names.
//
// XXX this kind of sucks because it means that anyone trying to use
// this without NSPR will get unresolved symbols when this library
// loads. It's also not very extensible. Oh well: FIX ME!
extern "C" {
// from nsprpub/pr/src/io/priometh.c (libnspr4.so)
extern void* _pr_faulty_methods;
};
static inline int
sanity_check_vtable_i386(void** vt)
{
// Now that we're "safe" inside the signal handler, we can
// start poking around. If we're really an object with
// RTTI, then the second entry in the vtable should point
// to a function.
//
// Let's see if the second entry:
//
// 1) looks like a 4-byte aligned pointer
//
// 2) points to something that looks like the following
// i386 instructions:
//
// 55 push %ebp
// 89e5 mov %esp,%ebp
// 53 push %ebx
//
// or
//
// 55 push %ebp
// 89e5 mov %esp,%ebp
// 56 push %esi
//
// (which is the standard function prologue generated
// by egcs, plus a ``signature'' instruction that appears
// in the typeid() function's implementation).
unsigned char** fp1 = reinterpret_cast<unsigned char**>(vt) + 1;
// Does it look like an address?
unsigned char* ip = *fp1;
if ((unsigned(ip) & 3) != 0)
return 0;
// Does it look like it refers to the standard prologue?
static unsigned char prologue[] = { 0x55, 0x89, 0xE5 };
for (unsigned i = 0; i < sizeof(prologue); ++i)
if (*ip++ != prologue[i])
return 0;
// Is the next instruction a `push %ebx' or `push %esi'?
return (*ip == 0x53 || *ip == 0x56);
}
static inline int
sanity_check_vtable_ppc(void** vt)
{
// XXX write me!
return 1;
}
#if defined(__i386)
# define SANITY_CHECK_VTABLE(vt) (sanity_check_vtable_i386(vt))
#elif defined(PPC)
# define SANITY_CHECK_VTABLE(vt) (sanity_check_vtable_ppc(vt))
#else
# define SANITY_CHECK_VTABLE(vt) (1)
#endif
const char* nsGetTypeName(void* ptr)
{
// sanity check the vtable pointer, before trying to use RTTI on the object.
void** vt = *(void***)ptr;
if (vt && !(unsigned(vt) & 3) && (vt != &_pr_faulty_methods)) {
Signaller s1(SIGSEGV);
if (attempt() == 0) {
if (SANITY_CHECK_VTABLE(vt)) {
// Looks like a function: what the hell, let's call it.
IUnknown* u = static_cast<IUnknown*>(ptr);
const char* type = typeid(*u).name();
// EGCS seems to prefix a length string.
while (isdigit(*type)) ++type;
return type;
}
}
}
return "void*";
}
#endif
#ifdef XP_WIN32
const char* nsGetTypeName(void* ptr)
{
//TODO: COMPLETE THIS
return "void*";
}
#endif //XP_WIN32