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Hello:

I am having problem trying to mix C and ASM code when I want to use global variables.

For example,

C code:

#include "myclib.h"
int NUM;
main() {
NUM=10;
printd(NUM); }

The printd() function is an NASM code (part of my OS).

I belive I have an error when I compile the program with this script:

nasm -f aout cheader.asm -o a.o
gcc -c -ffreestanding shell.c -o b.o
nasm -f aout clib.asm -o c.o
nasm -f aout cstack.asm -o d.o
ld -e start -Ttext 0x0000 --oformat binary -o shell.bin a.o b.o c.o d.o

cheader.asm just have a jump to _main,
shell.c is the program I want to compile,
clib.asm have all the syscalls to my kernel OS,
and cstack.asm just have space for the stack.

Any idea?

Thank you very much,

pepito

Not trying to be smart, but "I am having a problem mixing C and assembly" needs a bit more information about what is going on.  What problem, specifically is occuring and what other details (codewise) you can offer, would be helpful.

Sorry! The english is not my langage, but a will try to be more explicit...

I am using DJGPP and NASM to build a program that runs over my OS kernel. I need to get 'plain binary code' because my OS just can run this kind of programs.

But the program generate an error if I declare 'not initialized global variables' into the C code...

---

#include "myLibC.inc"

int NUM;   <-- global variable

main() {

NUM=1;     <-- here I get the error

} // main

---

...and then test my OS using BOCHS.

I get this kind of error:

    write_virtual_checks(): write beyond limit, r/w
    >>PANIC<< fetch_raw_descriptor: LDT: index (5af)b5 > limit (1f)

Or some other about bad address.

I suspect that the linker is not creating 'plain binary code' when I add 'not initialized global variables'. Then, when my program try to access this variables, it go to a bad address.

I use this script to compile my program:

nasm -f aout c_header.asm -o a.o        <-- header needed by my OS
gcc -c -ffreestanding shell.c -o b.o     <-- the C code of the program
nasm -f aout c_lib.asm -o c.o           <-- many ASM rutines
nasm -f aout c_stack.asm -o d.o         <-- the stack

ld -e start -Ttext 0x0000 --oformat binary -o shell.bin a.o b.o c.o d.o

Is better explained?

Thank you for your soon response!

pepito

Other details about the error:

- When I complie the C part of the program, DJGPP create .comm directives to hold the 'not initialized global variables'.

- If I read the address of the 'global variable' with the '&' operator, I get a value greater than the size of the program generated with the script!

pepito