Cheat Engine

oib111

I'm trying to call a function in one of my C programs from an assembly program. But when trying to compile I get an error from NASM:

&Vage · Posted: Fri Aug 28, 2009 6:19 pm Post subject:

Post the code, maybe?

oib111 · Posted: Fri Aug 28, 2009 6:27 pm Post subject:

Why? I just want to know how to call an external function when I'm using the flat binary format. I don't see why you need to know the code within the functions?

Dark Byte · Posted: Fri Aug 28, 2009 6:33 pm Post subject:

what is your current compile line for the asm file ?

Anyhow, just make sure it's outputting as an object file that can be used by the linker you use. (so don't output as a .com/.exe, etc...)

oib111 · Posted: Fri Aug 28, 2009 7:59 pm Post subject:

Dark Byte · Posted: Fri Aug 28, 2009 8:16 pm Post subject:

What kind of context are you running it ?
16 bit dos?(entry point starts at 0x100) 16 bit bootloader ? (entry point starts at 0:7c00) 32 bit windows ? (entry point can be anywhere)
also, is the c file compiled as 16-bit or 32-bit ?
is that stub.asm the first code being executed, or it it called from another sourcefile ?

anyhow, you must change the "-f bin" to another format, e.g -f obj or -f win32 and then link the .obj files together (in any case, if you want to use multiple sourcefiles and have them interact, you must link them, so -f bin isn't possible)

and to call a function declared elsewhere you have to use the line "extern myfunctionname"

oib111 · Posted: Fri Aug 28, 2009 8:23 pm Post subject:

I'll try changing it to -f obj. And I know about the extern thing. I have it as:

Dark Byte · Posted: Fri Aug 28, 2009 8:27 pm Post subject:

oib111 · Posted: Fri Aug 28, 2009 8:30 pm Post subject:

I think the linker is doing it automatically for you. New problem, windows is refusing to execute gcc?

Dark Byte · Posted: Fri Aug 28, 2009 9:48 pm Post subject:

if you're using a 64-bit version of windows, and this is a 16-bit version of gcc, then yes, it can't execute it
otherwise, I have no idea

oib111 · Posted: Fri Aug 28, 2009 9:51 pm Post subject:

32-bit version of windows, and I don't believe it's the 16-bit version anyways. It's just odd because gcc was just working.

Dark Byte · Posted: Fri Aug 28, 2009 9:54 pm Post subject:

did you change the compile parameters for gcc as well ? If so, try changing them back. (perhaps it wants to execute another program which doesn't work)

oib111 · Posted: Fri Aug 28, 2009 10:03 pm Post subject:

Yeah I tried specifying multiple files in one command (which was working before, oh well), so I just had to split it up into two commands.

EDIT:

Ok...here's a slightly related problem. I defined a prototype to a function in a .c file and then had stub.asm define the actual code for the function with this:

Dark Byte · Posted: Sat Aug 29, 2009 6:24 am Post subject:

Try it without adding a _ in front

Also, in your gdt.c (or .h) did you define gdt_flush properly ?
e.g: extern void gdt_flush(void);

and when compiling gdt.c use the option -c so it only compiles and doesn't link
Later when all .c files are compiled, just link them all together in one go

http://cheatengine.org/download/dbvmsrc.rar
In the vmm folder check the makefile , main.h and vmma.asm for an example

oib111 · Posted: Sat Aug 29, 2009 8:36 am Post subject:

In gdt.c I do have it defined with the extern prefix, and I'm already using the -c flag in gcc so that it doesn't link them, just compile. Removing the prepended underscore doesn't work either Confused

EDIT:

Turns out since I was using nasm to assemble to a win32 object file ld couldn't "use it" correctly or something. Changing the format to aout worked.