prime numbers

prime numbers

[Paul Irofti]

this is an exercies i set out to do in order to familiarise my self with 
linux and AT&T
assembly syntax.

i worked a lot and read a lot before figureing out how each operator 
gets its paramaters and such...

the code doesn't compile with the following errors:

# as -gstabs sieve.s -o sieve.o
# gcc sieve.o -o sieve
sieve.o(.text+0x1):sieve.s:20: relocation truncated to fit: R_386_8 .data
sieve.o(.text+0xc):sieve.s:24: relocation truncated to fit: R_386_16 .data
sieve.o(.text+0x19):sieve.s:32: relocation truncated to fit: R_386_8 .data
sieve.o(.text+0x1b):sieve.s:33: relocation truncated to fit: R_386_8 .data
sieve.o(.text+0x2d):sieve.s:43: relocation truncated to fit: R_386_8 .data
sieve.o(.text+0x39):sieve.s:50: relocation truncated to fit: R_386_8 .data
collect2: ld returned 1 exit status

the source code is:

# assembly code for the calculation of the primes numbers in the range of [2-100]
# the code brute forces the numbers out, no formulas are taken in consideration

*.include* "defines.h"		#system call numbers are stored here (i.e. __NR_<oper> = number)

*.global* main

*.data*

sieve:	
	*.byte* 4
test:
	*.byte* 1

*.text*

main:
	
loop:	
	movb $test, %dl
	incb %dl		#increase test
	movb %dl, (test)
	
	movw $sieve, %ax	#prepare for divb: move sieve in ax
	divb %dl		#div ax by dl
	
	xor %cx, %cx		#clear cx
	movb %ah, %cl		#move rest in cx
	
	jcxz next		#test if rest is 0 and increase if so
	
	movb $sieve, %al
	movb $test, %bl
	cmpb %al, %bl		#else test if "test" has reached sieve
	
	jnz loop		#if not go back and div by new test value
	
				
print:	movl $__NR_write, %eax  #else print the prime
	movl $1, %ebx		#STDOUT is $1
	xor %ecx, %ecx
	
	movb $sieve, %cl
	addb $30, %cl		#make ascii out of int
	
	movl $16,%edx		#buffer size
	int $0x80
	
next:	
	movb $sieve, %cl
	incb %cl		#increase sieve
	movb %cl, (sieve)
	
	movb $100, %al
	cmpb %al, %cl		#test if limit is reached
	jz exit
			
	movb $1, %al		#if not start again with a new sieve and test = 1
	movb %al, (test)
	
	jmp loop
	
exit:	movl $0, %eax
	ret
	

please send me any critique and advices you can, i really want to make 
the complete switch from MASM to GAS as soon as possible....

cheers!

Re: prime numbers

[Frank Kotler]

Paul Irofti wrote:

...
> sieve.o(.text+0x1):sieve.s:20: relocation truncated to fit: R_386_8 .data

...
>     movb $test, %dl

Pretty sure you want "movb test, %dl" - "$test" indicates that you're 
trying to move the *address* of your "test" variable (not the contents) 
into %dl... and it won't fit! (...etc.)

Best,
Frank

Re: prime numbers

[Paul Irofti]

Frank Kotler wrote:

> Paul Irofti wrote:
>
> ...
>
>> sieve.o(.text+0x1):sieve.s:20: relocation truncated to fit: R_386_8 
>> .data
>
>
> ...
>
>>     movb $test, %dl
>
>
> Pretty sure you want "movb test, %dl" - "$test" indicates that you're 
> trying to move the *address* of your "test" variable (not the 
> contents) into %dl... and it won't fit! (...etc.)
>
> Best,
> Frank
>
> -
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>
ok, so than what's the diffrence between:
a) movb $test, %al
b) movb test, %al
c) movb (test), %al
c) movb ($test), %al      #if this exists!

and how come when i access kernel ops i use $<oper>

i.e. movl $__NR_write, %eax    #i actually append the address 1?! not 
put the value 1?!

these are very confusing stuff for me. and i would greatly apreciate it 
if explained! thanks a lot Frank!

Re: prime numbers

[Frank Kotler]

Paul Irofti wrote:

...
> ok, so than what's the diffrence between:
> a) movb $test, %al
> b) movb test, %al
> c) movb (test), %al
> c) movb ($test), %al      #if this exists!

Hmmm, I'm actually Nasmist, not an as user, but...

> and how come when i access kernel ops i use $<oper>
> 
> i.e. movl $__NR_write, %eax    #i actually append the address 1?! not 
> put the value 1?!

I perhaps shouldn't have said "address"... As I understand it, the '$' 
indicates an "immediate" value. "movl $4, %eax" (or $__NR_write) moves 
the value 4 into %eax. "movl 4, %eax" would move the contents of address 
0x00000004 into %eax - except that it segfaults because 0x00000004 isn't 
in "your" address space.

Maybe an actual (G)as user can clarify it better. It *is* confusing - if 
it were easy, everybody'd be doing it! :)

Best,
Frank

Re: prime numbers

[Paul Irofti]

Frank Kotler wrote:

> Paul Irofti wrote:
>
> ...
>
>> ok, so than what's the diffrence between:
>> a) movb $test, %al
>> b) movb test, %al
>> c) movb (test), %al
>> c) movb ($test), %al      #if this exists!
>
>
> Hmmm, I'm actually Nasmist, not an as user, but...
>
>> and how come when i access kernel ops i use $<oper>
>>
>> i.e. movl $__NR_write, %eax    #i actually append the address 1?! not 
>> put the value 1?!
>
>
> I perhaps shouldn't have said "address"... As I understand it, the '$' 
> indicates an "immediate" value. "movl $4, %eax" (or $__NR_write) moves 
> the value 4 into %eax. "movl 4, %eax" would move the contents of 
> address 0x00000004 into %eax - except that it segfaults because 
> 0x00000004 isn't in "your" address space.
>
> Maybe an actual (G)as user can clarify it better. It *is* confusing - 
> if it were easy, everybody'd be doing it! :)
>
> Best,
> Frank
>
>
thanks man!

i had the same problems with syntax and address/value access in MASM 
when i started, now, i see myself hitting the same spot in the *nix 
world of assembly:))

well, i'm blown off, it's 6am here, i need some sleep, hopefully someone 
will make my morning..eh! afternoon... sweeter with a short lesson on 
the issue!

bye!