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Crash when calling AddScriptSection
Author
Hi all,
It's me agin. With another problem. When I try to add a script section the application crashes and gives the folliwing error message:
"Unhandled exception at 0x004ce06b in TestApp.exe: 0xC0000005: Access violation reading location 0x00000044."
When I run the debugger the Disassembly looks like (I've marked the line the debugger complains about):
"
...
...
...
asRet = asEnginePtr->AddScriptSection(script->m_module.c_str(),
script->m_name.c_str(),
script->m_scriptCode.c_str(),
script->m_scriptLength, 0, false);
004CE035 mov esi,esp
004CE037 push 0
004CE039 push 0
004CE03B mov eax,dword ptr [script]
004CE03E mov ecx,dword ptr [eax+1Ch]
004CE041 push ecx
004CE042 mov ecx,dword ptr [script]
004CE045 call std::basic_string<char,std::char_traits<char>,std::allocator<char> >::c_str (4964F4h)
004CE04A push eax
004CE04B mov ecx,dword ptr [script]
004CE04E add ecx,20h
004CE051 call std::basic_string<char,std::char_traits<char>,std::allocator<char> >::c_str (4964F4h)
004CE056 push eax
004CE057 mov ecx,dword ptr [script]
004CE05A add ecx,3Ch
004CE05D call std::basic_string<char,std::char_traits<char>,std::allocator<char> >::c_str (4964F4h)
004CE062 push eax
004CE063 mov edx,dword ptr [asEnginePtr]
004CE066 mov eax,dword ptr [edx]
004CE068 mov ecx,dword ptr [asEnginePtr]
004CE06B call dword ptr [eax+44h] <----------------- THIS IS THE LINE THE DEBUGGER COMPLAINS ABOUT
004CE06E cmp esi,esp
004CE070 call @ILT+14670(__RTC_CheckEsp) (497953h)
004CE075 mov dword ptr [asRet],eax
assert( asRet >= 0 );
...
...
..."
And the debugger points to the line I've marked above.
I've checked my code for NULL pointers but all pointers are valid.
The script variable in the AddScriptSection above i a class callde CScript and it is responsible for loading the script from an ordianry text file as follows:
HRESULT CScript::Load(const char *name, const char* module)
{
HRESULT hRet = S_OK;
// Set the name
m_name = string(name);
m_fullName = string(MEDIA_PATH) + string(name);
// Set the module
m_module = string(module);
// Load the script file
FILE *f = fopen(m_fullName.c_str(), "rb");
if (f != NULL){
// Get the length of the script file
fseek(f, 0, SEEK_END);
m_scriptLength = ftell(f);
fseek(f, 0, SEEK_SET);
// Copy the file data
m_scriptCode.resize(m_scriptLength);
if (fread(&m_scriptCode[0], m_scriptLength, 1, f) == 0) {
G_TRACE_1("CScript::Load : Failed to load script %s\n", m_fullName.c_str());
hRet = E_FAIL;
}
}
else {
G_TRACE_1("CScript::Load : Failed to open script %s\n", m_fullName.c_str());
hRet = E_FAIL;
}
// Close the file
fclose(f);
return hRet;
}
Before I call the AddScriptSection I've validated the script and asEnginePtr variable and checked all parameters and they are all valid. I also print out the actual script->m_scriptCode.c_str() and it gives the contents of the script text file.
I simply have no ideas as to what is wrong. Any ideas anyone?
Best Regards,
Risto Hietanen
Your code for loading the script looks just fine.
You're application crashes just on the moment when the virtual method AddScriptSection() is called, all the parameters have been successfully evaluated and pushed on the stack.
asEnginePtr may not be null, but it's vtable certainly is. The application is trying to read the function address for AddScriptSection from memory location 0x00000044, which tells me that it is using a vtable pointer = 0. Examine the first DWORD in the engine object that asEnginePtr is pointing to, you'll see that it is null, which is an invalid value.
The most likely cause of this is that somewhere in your code you're writing outside allocated memory, which overwrites the first bytes in the engine object. I suggest you set a break point for when the first bytes in asEnginePtr changes. This will allow you to catch the exact moment where the vtable is set to 0.
Regards,
Andreas
You're application crashes just on the moment when the virtual method AddScriptSection() is called, all the parameters have been successfully evaluated and pushed on the stack.
asEnginePtr may not be null, but it's vtable certainly is. The application is trying to read the function address for AddScriptSection from memory location 0x00000044, which tells me that it is using a vtable pointer = 0. Examine the first DWORD in the engine object that asEnginePtr is pointing to, you'll see that it is null, which is an invalid value.
The most likely cause of this is that somewhere in your code you're writing outside allocated memory, which overwrites the first bytes in the engine object. I suggest you set a break point for when the first bytes in asEnginePtr changes. This will allow you to catch the exact moment where the vtable is set to 0.
Regards,
Andreas
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