c - StackWalk64 on Windows - Get symbol name

Question

Alright, second question on SO in one day. Looks like Windows programming makes me happy... : S

I'm currently trying to get the function call stack on a Win32 executable.

This morning, I've also asked a question about this:

Win32 - Backtrace from C code

Now, I'm pretty sure that the StackWalk64 function is the key for this. I've read some articles on how to use it, as well as the MS documentation.

It actually displays frames on my test program, so it kinda work...

The problem is that I'm not able to retrieve the symbol name from the stack informations.

I'm using the SymGetSymFromAddr64 function for this, with UnDecorateSymbolName. But I only get junk characters.

Here's my code. Hope its not to messy, as I'm not used to Windows programming:

void printStack( void )
{
    BOOL                result;
    HANDLE              process;
    HANDLE              thread;
    CONTEXT             context;
    STACKFRAME64        stack;
    ULONG               frame;
    IMAGEHLP_SYMBOL64   symbol;
    DWORD64             displacement;
    char name[ 256 ];

    RtlCaptureContext( &context );
    memset( &stack, 0, sizeof( STACKFRAME64 ) );

    process                = GetCurrentProcess();
    thread                 = GetCurrentThread();
    displacement           = 0;
    stack.AddrPC.Offset    = context.Eip;
    stack.AddrPC.Mode      = AddrModeFlat;
    stack.AddrStack.Offset = context.Esp;
    stack.AddrStack.Mode   = AddrModeFlat;
    stack.AddrFrame.Offset = context.Ebp;
    stack.AddrFrame.Mode   = AddrModeFlat;

    for( frame = 0; ; frame++ )
    {
        result = StackWalk64
        (
            IMAGE_FILE_MACHINE_I386,
            process,
            thread,
            &stack,
            &context,
            NULL,
            SymFunctionTableAccess64,
            SymGetModuleBase64,
            NULL
        );

        symbol.SizeOfStruct  = sizeof( IMAGEHLP_SYMBOL64 );
        symbol.MaxNameLength = 255;

        SymGetSymFromAddr64( process, ( ULONG64 )stack.AddrPC.Offset, &displacement, &symbol );
        UnDecorateSymbolName( symbol.Name, ( PSTR )name, 256, UNDNAME_COMPLETE );

        printf
        (
            "Frame %lu:
"
            "    Symbol name:    %s
"
            "    PC address:     0x%08LX
"
            "    Stack address:  0x%08LX
"
            "    Frame address:  0x%08LX
"
            "
",
            frame,
            symbol.Name,
            ( ULONG64 )stack.AddrPC.Offset,
            ( ULONG64 )stack.AddrStack.Offset,
            ( ULONG64 )stack.AddrFrame.Offset
        );

        if( !result )
        {
            break;
        }
    }
}

The actual output is:

Frame 0:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠
    PC address:     0x00BA2763
    Stack address:  0x00000000
    Frame address:  0x0031F7E8

Frame 1:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠?
    PC address:     0x00BB4FFF
    Stack address:  0x00000000
    Frame address:  0x0031F940

Frame 2:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠?
    PC address:     0x00BB4E2F
    Stack address:  0x00000000
    Frame address:  0x0031F990

Frame 3:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠?
    PC address:     0x75BE3677
    Stack address:  0x00000000
    Frame address:  0x0031F998

Frame 4:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠?
    PC address:     0x770F9D72
    Stack address:  0x00000000
    Frame address:  0x0031F9A4

Frame 5:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠?
    PC address:     0x770F9D45
    Stack address:  0x00000000
    Frame address:  0x0031F9E4

Frame 6:
    Symbol name:    ╠╠╠╠╠╠╠╠╠╠╠╠?
    PC address:     0x770F9D45
    Stack address:  0x00000000
    Frame address:  0x0031F9E4

Seems weird that the stack address is always 0 by the way... Any help appreciated : )

Thanks to everyone!

EDIT

I'm looking for a plain C solution, without third party libraries...

Answer 1

You have set symbol.MaxNameLength to 255, but you allocated "symbol" on the stack with IMAGEHLP_SYMBOL64 symbol;. That type is defined as:

typedef struct _IMAGEHLP_SYMBOL64 {
  DWORD   SizeOfStruct;
  DWORD64 Address;
  DWORD   Size;
  DWORD   Flags;
  DWORD   MaxNameLength;
  TCHAR   Name[1];
} IMAGEHLP_SYMBOL64;

Notice that the Name field only has one character by default. If you want to store bigger names, you need to do something like:

 const int MaxNameLen = 255;
 IMAGEHLP_SYMBOL64* pSymbol = 
       malloc(sizeof(IMAGEHLP_SYMBOL64)+MaxNameLen*sizeof(TCHAR));
 pSymbol->MaxNameLength = MaxNameLen;

Otherwise, SymGetSymFromAddr64() is likely to overwrite memory. Here is what the help page for the structure says (emphasis added):

MaxNameLength: The maximum length of the string that the Name member can contain, in characters, not including the null-terminating character. Because symbol names can vary in length, this data structure is allocated by the caller. This member is used so the library knows how much memory is available for use by the symbol name.