<Int 16h> BIOS interruption with GCC Assembly in Linux?

Question

I'm using QTCreator 3.5.1 and a virtual OS which is Linux Mint 18.3 Cinnamon 32-bit, GCC Compiler.

I have to write a code that uses interruptions, obtaining a key pressed on the keyboard using assembly commands.

The code that should've been working on windows is like this:

#include <iostream>
unsigned char x;
int main()
{
 do {
 __asm {
 mov ah, 00h
 int 16h
 mov x, ah
 };
 std::cout <<"The pressed key code is "<< x << std::endl;
 } while (true);
}

Although it doesn't work on either Windows 98, compiled using Visual Studio 2003 on Windows 7x32, and any other Windows systems, giving me a runtime error or shutting my system down (on Windows 98).

So I switched to Linux and the following assembly example code from http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html (part 7) is working pretty much fine :

#include <iostream>
using std::cout;
int main(void)
{
        int foo = 10, bar = 15;
        __asm__ __volatile__("addl  %%ebx,%%eax"
                             :"=a"(foo)
                             :"a"(foo), "b"(bar)
                             );
        printf("foo+bar=%d\n", foo);
        return 0;
}

(For it to work properly I also had to specify the compiler version (GCC x86 32bit in usr/bin) on "Desktop Kit" in QT Creator Tool->Options and a working QT version which is 4.8.7, the last version 5.5.1 giving me a "non properly installed, please run make install" error)

Although I struggle to understand the concept of interruptions and how should the "int 16h" interruption work on linux with GCC inline assembly, what is the syntax and how I can obtain any pressed keyboard key code?

As you're working with Qt (apparently), wouldn't it be more appropriate to use something like this, rather trying to capture keyboard events at bios level (which is unlikely to be configured at the same interrupt in different operating systems). — πάντα ῥεῖ
int 16h is a BIOS service. It only works in real mode and is usually used in boot loaders or DOS programs. It cannot be accessed from neither Windows (any version, unless executing a DOS program in which case the service is emulated) or Linux (any version) or any other protected mode operating system for that matter. — fuz
Does the exercise specify that you have to use int 16h? What other details are given? You can read input using inline assembly on Linux (though I would not recommend doing so outside of an academic exercise). On Windows, this too is possible but the correct call depends on the Windows version. — fuz
@fuz, yes. This is the problem, my academic exercise does specify that I have to use int 16h — Ivan Silkin
@IvanSilkin Try coaxing Visual Studio into generating a Win16 or DOS application. — fuz

fuz fuz · Accepted Answer · 2020-12-27T11:59:51

The service int 16h is a BIOS service. It only works in real mode and is usually used in boot loaders or DOS programs. It cannot be accessed from neither Windows (any version, unless executing a DOS program in which case the service is emulated) or Linux (any version) or any other protected mode operating system for that matter.

According to the folks on #winapi at Freenode, it might have been possible to call int 16h from a Win32 program on Windows 98, but the call might then produce a hang in the BIOS. Anyway, this is not useful for achieving your goal.

To solve your problem, either write a DOS program using a DOS toolchain such as ia16-gcc, Open Watcom, or an old version of MSVC, or use a protected mode service supported by the operating system you are programming for.

<Int 16h> BIOS interruption with GCC Assembly in Linux?

2 Answers