task switch using gcc inline assembler

[crackers]

I've created TSS segment and using

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asm("call $0x80,$0");

where 0x80 is proper selector to TSS segment I can switch task. I want to have it parametrised, but i don't know how do this using gcc in;line assembler.
I've found something like this

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__asm__ __volatile__ ( "ljmp *(%0)": :"g" ((DWORD *)&selector) );

Unfortunately it's not working.

[YeXo]

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__asm__ __volatile__ ( "ljmp *(%0)": :"g" ((DWORD *)&selector) );

This is another line of asm than your first (I mean they do different things). If you want a call segment,0 your inline assembly should be something like this (I don't whether this will work or needs some tweaking):

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__asm__ __volatile__ ( "call (%0),0": :"g" (selector) );

where selector contains 0x80 in your example

[crackers]

I'm getting "Error : '(%ax)' is not a valid base/index expression" so I've tried to change constraints to

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__asm__ __volatile__ ( "call (%0),0": :"b" (selector) );
__asm__ __volatile__ ( "call (%0),0": :"S" (selector) );
__asm__ __volatile__ ( "call (%0),0": :"D" (selector) );

b - bx, S - si, D - di, but then I'm getting "Too many memory references for 'call' "
If nobody knows how to do this in inline assembler than maybe someone could tell me how to do it in NASM ?

[JoeKayzA]

Does it make a difference when you try to remove the brackets around '%0' (and using "g")? 'Selector' is an integer variable, not a pointer (I assume, at least), so you should reference it without the brackets.

cheers Joe

[crackers]

Does it make a difference when you try to remove the brackets around '%0' (and using "g")? 'Selector' is an integer variable, not a pointer (I assume, at least), so you should reference it without the brackets.

Yes, 'selector' is unsigned short

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__asm__ __volatile__ ( "call %0,0": :"g" (selector) );

Upon this code I'm getting "Error: sufix or operands invalid for 'call' "

[paulbarker]

lcall? I know you use ljmp rather than jmp for a far jump, so I assume you use lcall for a far call.

The 'l' is an L. Confusing fonts.

[crackers]

I'm still getting the same error :-\

[crackers]

I did it in NASM

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mov ebx, task_address
call word far [ebx]
....
task_address: 
.offset: dw 0
.segment: dw 0

[nicesj]

hello

I wrote a code for task-switching.

#define switch_task(a) __asm__ volatile("jmp %0,$0"::"i"(a))

good luck with you.

http://nicesj.com (euc-kr)

[Pype.Clicker]

use of "call xxx" is strongly discouradged in the case of multitasking. Outgoing TSS will be marked as busy, meaning that you can't "call" it again.

[crackers]

Well I'm using two versions jmp and call - depend on situation.