Since this newsgroup is *determined* to talk about C recently, the
*least* we can do is call some asm from it!
Us "purists" don't like it much, but in the real world, most asm is in
subroutines called from C[++]. The hard parts are done in asm, and C[++]
provides the "glue" that holds it together, and provides the OS-specific
parts. (not going to be ****table across CPUs, of course)
An alternative to this would be inline asm. When the C folks talk about
****tability, they ain't talking about cross-toolchain ****tability of
inline asm!!! Awful mess. Maybe gcc on Linux (BSD/Mac) vs gcc on Windows
would work...
An object file of the proper format will (should) link with object
file(s) of the same format, regardless of *what* language the were
written in ("Python" is popular... I wanna wrestle a carniverous reptile
that outweighs me... Yeah, right!). Different kind of "****tability".
Since Nasm will produce object files in a variety of formats, it's a
suitable tool for the asm part. We won't have "binary ****tability" of
course, it'll have to be re-assembled for each OS we want to use it with
(same as C)...
I don't suppose C has a "getcpuvendor()"... maybe it does. Struck me as
something this might be "good for". (a better example might pass more
parameters...) Something like:
bits 32
global getvendor
section .text
getvendor:
pusha
xor eax, eax
cpuid
mov eax, [esp + 36]
mov [eax], ebx
mov [eax + 4], edx
mov [eax + 8], ecx
mov byte [eax + 12], 0
popa
xor eax, eax
ret
For Linux, we can assemble this as "nasm -f elf getvendor.asm" - add
"-g" or "-O" switches if you want... For other-than-ELF, we probably
want an underscore on "getvendor", so "nasm -f win32 --prefix _
getvendor.asm". I'm not sure if MacIntel wants underscores for "-f
macho" or not. If my information is correct, Watcom C wants a *trailing*
underscore... "--postfix _" should do it. Hmmmm, what output format
would Watcom want? Hmmm... Borland wants "-f obj", I believe. "-f obj"
defaults to "bits 16", so we'll need "bits 32" if we want it to work
with "-f obj" - won't hurt "-f elf", etc... There, I put it in
(improving already!).
Now, we'll want something to call it from...
main()
{char vendorbuf[13];
getvendor(vendorbuf);
puts(vendorbuf);
}
gcc -o getvendortest getvendortest.c getvendor.o
That's horribly improper C. Won't tolerate "-Wall". We'll want "int
main"... "puts" is implicitly declared in "stdio.h", I guess. We could
include a "getvendor.h"... hardly seems worthwhile. "Prototype" it here?
(before or after "main"...?) An explict "return". What's the "minimal"
but "correct" way to do it?
I don't know how to call it from VB or whateverall... any gurus? Hey, we
can call it from asm!
global _start
extern getvendor
section .text
_start:
nop
commence:
push vendorbuf
call getvendor
add esp, 4
mov ecx, vendorbuf
mov edx, 12
call write_stdout
mov ebx, eax
mov eax, 1
int 80h
;------------------
write_stdout:
mov ebx, 1 ; STDOUT
mov eax, 4 ; __NR_write
int 80h
ret
;-------------------
section .bss
vendorbuf resb 13
;-----------------------
That'll have to be changed for other-than-Linux, of course. WriteFile...
put it in a window with some fancy font, if you like... Maybe, for
Windows, we ought to arrange for "ret 4" in the callee so it'd be more
like an API call?
Just a first draft...
Best,
Frank
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