Yesterday evening, I made a program in my programming language that can run on DOS. It's an analog clock again, similar to the previous one.
Here is what it looks like in QEMU:
![[Image: analogClockForDOS.png]](https://www.vogons.org/attachments/37715_3e30225ed33f2cfc6728d01db69e3065/analogClockForDOS.png)
Code:
Syntax GAS
;This is the same program as in the "analogClock.aec" file, just modified to
;run on DOS instead of Linux. It also compiles using GNU Assembler.
;Namely, GCC 9.3.0 and GNU Assembler 2.34, although they are released in
;2019, still feature the ability to compile for DOS. You don't need to
;run them on DOS for that, in fact, I doubt they even can be run on DOS.
;If you manage to compile them to run on DOS, they will probably run out of
;RAM even for the simplest programs (DOS can't use more than 64MB of RAM,
;which is far too little to run a modern compiler). You can run them on
;Linux and they will produce a DOS executable which you then can run in an
;emulator. That's called cross-compiling. Now, it's not possible to do with
;the stripped-down version of GNU Compiler Collection (GCC) you get with
;Linux, you need to build it from source to get all the features (among
;other things, cross-compilation to many OS-es). It's not too hard, but it
;does take hours to compile full version of GCC even on a super-modern
;computer. For some reason that escapes me, this particular executable
;causes DosBox to crash, even though it works on FreeDOS in VirtualBox.
;Now, I hope this goes without saying, but if some modern program runs on
;DOS, that's probably a coincidence, and you can't count on it working
;flawlessly. Developers have long stopped testing whether their app works
;under DOS. So, while the C library that comes with GCC 9.3.0 can compile
;for DOS, attempts to actually link with it lead to countless linker errors.
;GCC will by default attempt to link to the C library, even if your code
;doesn't use any of the functions present in it. So, you need to compile
;the assembly code ArithmeticExpressionCompiler produces with:
; djgpp-gcc -o analogClockForDOS.exe -ffreestanding -nostdlib analogClockForDOS.s
;For that reason, I wasn't able to compile Duktape to run on DOS.
;Why use GNU Assembler instead of FlatAssembler? Well, first of all, I
;already have tons of inline assembly compatible with GNU Assembler (from
;"analogClock.aec" which runs on Linux). Second, when you work in
;GNU Assembler, you don't have to write the complicated code for putting
;the processor in the 32-bit mode (DOS programs automatically start in
;16-bit mode), GNU Assembler does that for you.
;Now, in order for 32-bit apps to be able to run on DOS, you need to have
;a driver called DPMI (DOS Protected Mode Interface). It comes pre-installed
;in FreeDOS, but not on MS-DOS. It also comes with Windows 3.x.
;FlatAssembler for DOS is also a 32-bit app and it won't run on DOS without
;a DPMI installed and run.
AsmStart ;So, the following code is generated by GCC 9.3.0, plus some inline assembly I put in the C program.
.file "analogClock.c"
.section .text
/APP
.intel_syntax noprefix
call _main #I hope this goes without saying, but when you are developing...
#...for a system without a C library, there is no guarantee "main" will...
#...be called first (or even at all before your program crashes),
#you need to take care of that yourself.
.att_syntax
/NO_APP
.globl _putchar
_putchar:
LFB0:
.cfi_startproc
pushl %ebp
.cfi_def_cfa_offset 8
.cfi_offset 5, -8
movl %esp, %ebp
.cfi_def_cfa_register 5
subl $4, %esp
movl 8(%ebp), %eax
movb %al, -4(%ebp)
/APP
# 9 "analogClock.c" 1
movb -4(%ebp),%dl
movb $0x02,%ah
int $0x21
# 0 "" 2
/NO_APP
nop
leave
.cfi_restore 5
.cfi_def_cfa 4, 4
ret
.cfi_endproc
LFE0:
.comm result,4
.comm i,4
.comm x,4
.comm y,4
.comm currentSign,4
.comm centerX,4
.comm centerY,4
.comm distance,4
.comm clockRadius,4
.comm output,7360
.comm hour,4
.comm minute,4
.comm second,4
.comm angle,4
.comm endOfTheHandX,4
.comm endOfTheHandY,4
.comm coefficientOfTheDirection,4
.comm windowWidth,4
.comm windowHeight,4
.comm lowerBoundX,4
.comm upperBoundX,4
.comm lowerBoundY,4
.comm upperBoundY,4
.comm isXWithinBounds,4
.comm isYWithinBounds,4
.comm expectedY,4
.comm expectedX,4
.comm j,4
.comm ASCIIofSpaceAsFloat32,4
.comm ASCIIofDigit0AsFloat32,4
.comm ASCIIofColonAsFloat32,4
.comm ASCIIofNewLineAsFloat32,4
.globl _main
_main:
LFB1:
.cfi_startproc
pushl %ebp
.cfi_def_cfa_offset 8
.cfi_offset 5, -8
movl %esp, %ebp
.cfi_def_cfa_register 5
subl $24, %esp
/APP
# 18 "analogClock.c" 1
.ifdef debugForDOS #When you don't have a good debugger (like when working on DOS), you need to find some clever ways to debug. You know, like printing "Hello world!" step by step.
.intel_syntax noprefix
mov dl,'H'
mov ax,0x200
int 0x21
.att_syntax
.endif
.intel_syntax noprefix #Get current time. As we have no access to the standard C library here, we need to look up a way to do that in DOS API.
mov ax,0x2C00
int 0x21
mov byte ptr hour,ch
fild dword ptr hour
fstp dword ptr hour
mov byte ptr minute,cl
fild dword ptr minute
fstp dword ptr minute
mov byte ptr second,dh
fild dword ptr second
fstp dword ptr second #Eh, now I understand why some assembly-language programmers prefer att_syntax to intel_syntax (no need to write "dword ptr" there).
#Let's also set the graphic card to text-mode, in case it isn't in it (though I don't know if it's possible to invoke my program from some other mode without crashing DOS before my program even begins then).
mov ax,0x0003
int 0x10
.att_syntax
AsmEnd ;And now finally follows a program written in AEC.
windowWidth:=80
windowHeight:=23
ASCIIofSpace<=" \0\0\0" ;As integer. We know we are dealing with a...
ASCIIofNewLine<="\n\0\0\0" ;32-bit little-endian machine.
ASCIIofStar<="*\0\0\0"
i:=0
While i<windowWidth*windowHeight ;First, fill the window with spaces and newlines.
If mod(i,windowWidth)=windowWidth-1
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofSpace #Not need for a new line, DOS will do that automatically.
fstp dword ptr currentSign
.att_syntax
AsmEnd
Else
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofSpace
fstp dword ptr currentSign
fld dword ptr currentSign
fstp dword ptr ASCIIofSpaceAsFloat32
.att_syntax
AsmEnd
EndIf
output[i]:=currentSign
i:=i+1
EndWhile
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'e'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
centerX:=windowWidth/2-mod(windowWidth/2,1)
centerY:=windowHeight/2-mod(windowHeight/2,1)
clockRadius:=(centerX<centerY)?(centerX):(centerY)-1
i:=0
While i<windowWidth*windowHeight ;Next, draw the circle which represents the clock.
y:=i/windowWidth-mod(i/windowWidth,1) ;When I didn't put "floor" into my programming language...
x:=mod(i,windowWidth)
distance:=sqrt((x-centerX)*(x-centerX)+(y-centerY)*(y-centerY)) ;Pythagorean Theorem.
If abs(distance-clockRadius)<3/4
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofStar
fstp dword ptr currentSign
.att_syntax
AsmEnd
output[i]:=currentSign
EndIf
i:=i+1
EndWhile
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'l'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
AsmStart
.intel_syntax noprefix
jmp ASCIIofDigitsAsInt32Array$
ASCIIofDigitsAsInt32Array:
.macro writeDigits startingWith=0
.byte '0'+\startingWith,0,0,0 #".byte" is to GNU Assembler about the same as "db" is to FlatAssembler.
.if \startingWith < 9
writeDigits \startingWith+1
.endif
.endm
writeDigits #The goal is to make Assembler output the ASCII of "0\0\0\01\0\0\02\0\0\0...9\0\0\0" inside the executable (if the instruction pointer points to it, it will, of course, be an invalid instruction).
ASCIIofDigitsAsInt32Array$:
.att_syntax
AsmEnd
;Label of "12"...
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+1*4] #The ASCII of '1'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
output[(centerY-clockRadius+1)*windowWidth+centerX]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+2*4] #The ASCII of '2'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
output[(centerY-clockRadius+1)*windowWidth+centerX+1]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+6*4] #The ASCII of '6'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
output[(centerY+clockRadius-1)*windowWidth+centerX]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+3*4] #The ASCII of '3'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
output[centerY*windowWidth+centerX+clockRadius-1]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+9*4] #The ASCII of '9'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
output[centerY*windowWidth+centerX-clockRadius+1]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+1*4] #The ASCII of '1'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1)*cos(360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(360/12)*(clockRadius-1)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+2*4] #The ASCII of '2'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1.5)*cos(2*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(2*360/12)*(clockRadius-1.5)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+4*4] #The ASCII of '4'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1)*cos(4*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(4*360/12)*(clockRadius-1)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+5*4] #The ASCII of '5'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1)*cos(5*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(5*360/12)*(clockRadius-1)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+7*4] #The ASCII of '7'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1)*cos(7*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(7*360/12)*(clockRadius-1)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+8*4] #The ASCII of '8'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1)*cos(8*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(8*360/12)*(clockRadius-1)]:=currentSign
;Label "10"...
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+1*4] #The ASCII of '1'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1.5)*cos(10*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(10*360/12)*(clockRadius-1.5)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+0*4] #The ASCII of '0'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1.5)*cos(10*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(10*360/12)*(clockRadius-1.5)+1]:=currentSign
;Label "11"...
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+1*4] #The ASCII of '1'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1.5)*cos(11*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(11*360/12)*(clockRadius-1.5)]:=currentSign
AsmStart
.intel_syntax noprefix
fild dword ptr [ASCIIofDigitsAsInt32Array+1*4] #The ASCII of '1'.
fstp dword ptr currentSign
.att_syntax
AsmEnd
y:=centerY-(clockRadius-1.5)*cos(11*360/12)
y:=y-mod(y,1)
output[y*windowWidth+centerX+sin(11*360/12)*(clockRadius-1.5)+1] := currentSign
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'o'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
j:=0
While j<3
If j=0
angle:=(mod(hour+minute/60,12))*(360/12)
ElseIf j=1
angle:=minute*(360/60)
Else
angle:=second*(360/60)
EndIf
endOfTheHandX:=centerX+sin(angle)*clockRadius/(j=0?2:j=1?3/2:4/3) ;Hour hand will be the shortest, and the hand that shows the seconds will be the longest.
endOfTheHandY:=centerY-cos(angle)*clockRadius/(j=0?2:j=1?3/2:4/3)
coefficientOfTheDirection:=(endOfTheHandY-centerY)/(endOfTheHandX-centerX)
debugString <= "Drawing line between (%d,%d) and (%d,%d).\n\0"
AsmStart
.intel_syntax noprefix
.ifdef DEBUG #Conditional assembly, this will only be assembled if you tell GNU Assembler (by modifying the file or using command line) that you want to enable debugging.
fld dword ptr endOfTheHandY
fistp dword ptr result
push dword ptr result #This (pushing a "dword" onto the system stack) breaks the compatibility with 64-bit Linux (but you can still enable it by disabling debugging)!
fld dword ptr endOfTheHandX
fistp dword ptr result
push dword ptr result
fld dword ptr centerY
fistp dword ptr result
push dword ptr result
fld dword ptr centerX
fistp dword ptr result
push dword ptr result
lea ebx,debugString
push ebx
call printf #I hope this goes without saying, but, unless you link with a C library, this won't work under DOS.
.endif #End of the conditional assembly.
.att_syntax
AsmEnd
i:=0
While i<windowWidth*windowHeight
lowerBoundX:=(endOfTheHandX<centerX)?(endOfTheHandX):(centerX)
upperBoundX:=(endOfTheHandX>centerX)?(endOfTheHandX):(centerX)
lowerBoundY:=(endOfTheHandY<centerY)?(endOfTheHandY):(centerY)
upperBoundY:=(endOfTheHandY>centerY)?(endOfTheHandY):(centerY)
y:=i/windowWidth-mod(i/windowWidth,1)
x:=mod(i,windowWidth)
isXWithinBounds:=(x>lowerBoundX | x=lowerBoundX) & (x<upperBoundX | x=upperBoundX) ;Damn... Now I understand why almost every programming language supports the "<=" and ">=" operators, no matter how much harder they make the language to tokenize.
isYWithinBounds:=(y>lowerBoundY | y=lowerBoundY) & (y<upperBoundY | y=upperBoundY)
If isXWithinBounds=1 & isYWithinBounds=1
expectedY:=(x-centerX)*coefficientOfTheDirection+centerY
expectedX:=(y-centerY)*(1/coefficientOfTheDirection)+centerX
debugString1 <= "The point (%d,%d) is within bounds, expectedY is %d and expectedX is %d.\n\0"
AsmStart
.intel_syntax noprefix
.ifdef DEBUG
fld dword ptr expectedX
fistp dword ptr result
push dword ptr result
fld dword ptr expectedY
fistp dword ptr result
push dword ptr result
fld dword ptr y
fistp dword ptr result
push dword ptr result
fld dword ptr x
fistp dword ptr result
push dword ptr result
lea ebx,debugString1
push ebx
call printf
.endif
.att_syntax
AsmEnd
ASCIIofLetterH<="h\0\0\0"
ASCIIofLetterM<="m\0\0\0"
ASCIIofLetterS<="s\0\0\0"
If j=0
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofLetterH
fstp dword ptr currentSign
.att_syntax
AsmEnd
ElseIf j=1
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofLetterM
fstp dword ptr currentSign
.att_syntax
AsmEnd
Else
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofLetterS
fstp dword ptr currentSign
.att_syntax
AsmEnd
EndIf
If (upperBoundX=lowerBoundX | upperBoundY=lowerBoundY) & output[i]=ASCIIofSpaceAsFloat32
output[i]:=currentSign
EndIf
If (abs(expectedY-y)<3/4 | abs(expectedX-x)<3/4) & output[i]=ASCIIofSpaceAsFloat32
output[i]:=currentSign
EndIf
EndIf
i:=i+1
EndWhile
j:=j+1
EndWhile
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,' '
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
;Draw some ornament...
ASCIIofLetterX<="x\0\0\0"
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofLetterX
fstp dword ptr currentSign
.att_syntax
AsmEnd
i:=0
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'w'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
While i<windowWidth*windowHeight
y:=i/windowWidth-mod(i/windowWidth,1)
x:=mod(i,windowWidth)
If abs(windowHeight-2*ln(1+abs((x-centerX)/2))-y)<1-abs(x-centerX)/(centerX*95/112) & x>1/2*centerX & x<3/2*centerX & output[i]=ASCIIofSpaceAsFloat32 ;The logarithmic curve looks somewhat like a lemma of a flower.
output[i]:=currentSign
EndIf
i:=i+1
EndWhile
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'o'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofLetterX
fstp dword ptr currentSign
.att_syntax
AsmEnd
;Let's try to make it look like the bottom of the lemma isn't floating in the air.
j:=0
While j<3
i:=windowWidth*(windowHeight-1) ;So, move to the beginning of the last line.
While i<windowWidth*windowHeight
If j<2 & (output[i-windowWidth]=currentSign & (output[i+1]=currentSign | output[i-1]=currentSign))
output[i]:=currentSign
ElseIf j=2 & (output[i+1]=ASCIIofSpaceAsFloat32 & output[i-windowWidth]=currentSign)
output[i]:=ASCIIofSpaceAsFloat32
EndIf
i:=i+1
EndWhile
j:=j+1
EndWhile
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'r'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
;Let's make a digital clock in the corner...
AsmStart
.intel_syntax noprefix
fild dword ptr ASCIIofDigitsAsInt32Array #So, load "0\0\0\0" (the first 32 bits of the array "ASCIIofDigitsAsInt32Array") into the st0 register and convert it to Float32.
fstp dword ptr ASCIIofDigit0AsFloat32
.att_syntax
AsmEnd
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'l'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
ASCIIofColon<=":\0\0\0"
AsmStart
.intel_syntax
fild dword ptr ASCIIofColon
fstp dword ptr ASCIIofColonAsFloat32
.att_syntax
AsmEnd
output[windowWidth*windowHeight-2]:=ASCIIofDigit0AsFloat32+mod(second,10)
output[windowWidth*windowHeight-3]:=ASCIIofDigit0AsFloat32+second/10-mod(second/10,1)
output[windowWidth*windowHeight-4]:=ASCIIofColonAsFloat32
output[windowWidth*windowHeight-5]:=ASCIIofDigit0AsFloat32+mod(minute,10)
output[windowWidth*windowHeight-6]:=ASCIIofDigit0AsFloat32+minute/10-mod(minute/10,1)
output[windowWidth*windowHeight-7]:=ASCIIofColonAsFloat32
output[windowWidth*windowHeight-8]:=ASCIIofDigit0AsFloat32+mod(hour,10)
output[windowWidth*windowHeight-9]:=ASCIIofDigit0AsFloat32+hour/10-mod(hour/10,1)
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'d'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
signature<="Analog Clock for DOS\nMade in AEC by\nTeo Samarzija\0"
currentSign:=signature[0]
i:=windowWidth*(windowHeight-3)
j:=0
While not(currentSign=0) ;That is, as long as it's not the '\0' sign.
AsmStart
.intel_syntax noprefix
fld dword ptr j
fistp dword ptr result
mov ebx, dword ptr result
movzx eax, byte ptr [signature+ebx] #I hope it goes without saying something like this (using post-Pentium instructions in inline assembly) won't work on a machine with an archaic processor. I am writing this program for a machine with a modern processor which happens to run DOS.
mov dword ptr result, eax
fild dword ptr result
fstp dword ptr currentSign
fild dword ptr ASCIIofNewLine
fstp dword ptr ASCIIofNewLineAsFloat32
.att_syntax
AsmEnd
If currentSign=ASCIIofNewLineAsFloat32
i:=(i/windowWidth-mod(i/windowWidth,1)+1)*windowWidth
ElseIf not(currentSign=0)
output[i]:=currentSign
i:=i+1
Else
output[i]:=ASCIIofSpaceAsFloat32
EndIf
j:=j+1
EndWhile
AsmStart
.intel_syntax noprefix
.ifdef debugForDOS
mov dl,'!'
mov ax,0x200
int 0x21
.endif
.att_syntax
AsmEnd
AsmStart ;And this is, according to GCC 9.3.0, how you convert a Float32Array with ASCII codes and print it under DOS.
# 0 "" 2
/NO_APP
movl $0, -4(%ebp)
jmp L3
L4:
movl -4(%ebp), %eax
flds output(,%eax,4)
fnstcw -18(%ebp)
movw -18(%ebp), %ax
orb $12, %ah
movw %ax, -20(%ebp)
fldcw -20(%ebp)
fistps -22(%ebp)
fldcw -18(%ebp)
movb -22(%ebp), %al
movsbl %al, %eax
pushl %eax
call _putchar
addl $4, %esp
incl -4(%ebp)
L3:
cmpl $1839, -4(%ebp)
jle L4
/APP
# 21 "analogClock.c" 1
.intel_syntax noprefix
mov al,0 #And I hope this also goes without saying, but when there is...
mov ah,0x4C #...no C library, returning 0 from "main" crashes your program...
int 0x21 #...and you need to use OS-specific code to end it properly.
.att_syntax
# 0 "" 2
/NO_APP
movl $0, %eax
leave
.cfi_restore 5
.cfi_def_cfa 4, 4
ret
.cfi_endproc
LFE1:
.ident "GCC: (GNU) 9.3.0"
AsmEnd
