Borland x86 inlined assembler; get a label's address?

Question

I am using Borland Turbo C++ with some inlined assembler code, so presumably Turbo Assembler (TASM) style assembly code. I wish to do the following:

void foo::bar( void )
{
    __asm
    {
      mov eax, SomeLabel
      // ...
    }
    // ...
SomeLabel:
    // ...
}

So the address of SomeLabel is placed into EAX. This doesn't work and the compiler complains of: Undefined symbol 'SomeLabel'.

In Microsoft Assembler (MASM) the dollar symbol ($) serves as the current location counter, which would be useful for my purpose. But again this does not seem to work in Borlands Assember (expression syntax error).

Update: To be a little more specific, I need the compiler to generate the address it moves into eax as a constant during compilation/linking and not at run time, so it will compile like "mov eax, 0x00401234".

Can anybody suggest how to get this working?

UPDATE: To respond to Pax's question (see comment), If the base address is changed at run time by the Windows loader the DLL/EXE PE image will still be relocated by the Windows loader and the labels address will be patched at run time by the loader to use the re-based address so using a compile/link time value for the label address is not an issue.

Many thanks in advance.

Answer 1

Last time I tried to make some assembly code Borland-compatible I came across the limitation that you can't forward-reference labels. Not sure if that's what you're running into here.

Answer 2

Everything I can find about Borland suggests this ought to work. Similar questions on other sites (here and here) suggest that Borland can handle forward-references for labels, but insists on labels being outside asm blocks. However, as your label was already outside the asm block...

I am curious whether your compiler would allow you to use this label within, for instance, a jmp instruction. When toying around with it (admittedly, on a completely different compiler), I found a pesky tendency for the compiler to complain about operand types.

The syntax is quite different, and it's my first attempt at inline asm in a long time, but I believe I've munged this enough to work under gcc. Perhaps, despite the differences, this might be of some use to you:

#include <stdio.h>
int main()
{
    void *too = &&SomeLabel;
    unsigned int out;
    asm
    (
      "movl %0, %%eax;"
      :"=a"(out)
      :"r"(&&SomeLabel)
    );
SomeLabel:
    printf("Result: %p %x\n", too, out);

    return 0;
}

This generates:

...
        movl    $.L2, %eax
...
.L2:

The && operator is a non-standard extension, I wouldn't expect it to work anywhere other than gcc. Hopefully this may have stirred up some new ideas... Good luck!

Edit: Though it's listed as Microsoft specific, here is another instance of jumping to labels.