Assembly with C/C++

Baxos · Post by **Baxos** » Fri Mar 07, 2008 11:57 am

Hi guys...
I'm new here, i just started on some simple os but im kinda stuck with it right now.. i read some tutorial of making a assembly boot file and it works great and i have added some key interrupts to it in assembly only.. Now im kinda stuck at getting assembly and C working together
i know that i shall use c files in assembly with something like this
[extern C-FILE]
and then just call void's with call _xxx
but i cant get it to work? Maybe my linking is the problem please help me
Thankes

cyr1x · Post by **cyr1x** » Fri Mar 07, 2008 12:48 pm

Post the error message's !

jzgriffin · Post by **jzgriffin** » Fri Mar 07, 2008 1:24 pm

Yes, please do.

Code: Select all

[extern C-FILE]

That looks wrong. You shouldn't be extern'ing the C file's name, but individual functions, example:

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[extern main]
call main

01000101 · Post by **01000101** » Fri Mar 07, 2008 3:01 pm

don't forget the '_' suffix, assuming that is a standard and not just a nasm thing.

jzgriffin · Post by **jzgriffin** » Fri Mar 07, 2008 3:11 pm

You should only need _ if you're working with formats like COFF, AOUT, etc. It shouldn't be necessary with ELF. If you're using DJGPP without ELF support, for example, you will need _. But if you're using Cygwin with a cross compiler, _ won't be needed. The same goes for pretty much any Linux compilation of GCC/Binutils.

nekros · Post by **nekros** » Fri Mar 07, 2008 3:43 pm

I believe you should refine your asm skills, and maybe programming in general since you seem to have problems with EXTERN.

Alboin · Post by **Alboin** » Fri Mar 07, 2008 4:01 pm

nekros wrote:I believe you should refine your asm skills, and maybe programming in general since you seem to have problems with EXTERN.

EXTERN can be tricky!

... wait a minute ...

And guess what it did? It boiled, mother.

nekros · Post by **nekros** » Fri Mar 07, 2008 4:05 pm

I think that was sarcasm, I'm not sure though.

DeletedAccount · Post by **DeletedAccount** » Sat Mar 08, 2008 1:13 am

Griffin is correct , you do not need the underscore when working with PE and elf formats . you may use the global directive to use asm from C code

eg
GLOBAL my_func

Also .. I think there is a option in gcc to eliminate underscores , something like -fnoleadingunderscores ... i do not remember exactly ... May be,Solar knows this well.

jzgriffin · Post by **jzgriffin** » Sat Mar 08, 2008 2:47 am

You can either force leading underscores (-fleading-underscore) or disable them entirely (-fno-leading-underscore).

Baxos · Post by **Baxos** » Sat Mar 08, 2008 3:22 am

baxos@debian:~/baxos$ nasm test.asm -o Bootloader
test.asm:110: warning: label alone on a line without a colon might be in error
test.asm:123: warning: label alone on a line without a colon might be in error
test.asm:136: warning: label alone on a line without a colon might be in error
test.asm:147: warning: label alone on a line without a colon might be in error
test.asm:11: error: binary output format does not support external references

the code i have on line 11 is :
call _TEST
and i use [extern _TEST]

JamesM · Post by **JamesM** » Sat Mar 08, 2008 9:27 am

Code: Select all

nasm -f elf test.asm -o Bootloader