assembly studs

[Sirrius]

I have a bunch of assembly code here that I was trying to convert from AT&T to NASM. Could somebody please see if I have made any obvious mistakes? It doesnt seem to want to generate the output it supposed to. Thanks for your time and advice. B.

; .file "ByteSwap8.c"
global _ByteSwap8_asm
section .text

_ByteSwap8_asm:
PUSH ebp ;pushl %ebp
MOV ebp,esp ;movl %esp, %ebp
PUSH ebx ;pushl %ebx
SUB esp,28 ;subl $28, %esp
MOV dword [ebp-12],0 ;movl $0, -12(%ebp)
L2:
MOV eax,[ebp-12] ;movl -12(%ebp), %eax
CMP eax,[ebp+8] ;cmpl 8(%ebp), %eax
JL L5
JMP L1
L5:
MOV eax,[ebp-12] ;movl -12(%ebp), %eax
LEA edx,[0+eax+8] ;leal 0(,%eax,8), %edx
MOV eax,[ebp+12] ;movl 12(%ebp), %eax
LEA edx,[eax+edx] ;leal (%eax,%edx), %edx
MOV eax,[edx] ;movl (%edx), %eax
MOV edx,[edx+4] ;movl 4(%edx), %edx
MOV [ebp-24],eax ;movl %eax, -24(%ebp)
MOV [ebp-20],edx ;movl %edx, -20(%ebp)

MOV     al,\[ebp-24\]							;movb	-24(%ebp), %al
MOV     \[ebp-25\],al							;movb	%al, -25(%ebp)
MOV     al,\[ebp-23\]							;movb	-23(%ebp), %al
MOV     \[ebp-26\],al							;movb	%al, -26(%ebp)
MOV     al,\[ebp-22\]							;movb	-22(%ebp), %al
MOV     \[ebp-27\],al							;movb	%al, -27(%ebp)
MOV     al,\[ebp-21\]							;movb	-21(%ebp), %al
MOV     \[ebp-28\],al							;movb	%al, -28(%ebp)
MOV     al,\[ebp-20\]							;movb	-20(%ebp), %al
MOV     \[ebp-29\],al							;movb	%al, -29(%ebp)
MOV     al,\[ebp-19\]							;movb	-19(%ebp), %al
MOV     \[ebp-30\],al							;movb	%al, -30(%ebp)
MOV     al,\[ebp-18\]							;movb	-18(%ebp), %al
MOV     \[ebp-31\],al							;movb	%al, -31(%ebp)
MOV		al,\[ebp-17\]							;movb	-17(%ebp), %al
MOV		\[ebp-32\],al							;movb	%al, -32(%ebp)

MOV     eax,\[ebp-12\]						;movl	-12(%ebp), %eax
LEA     ebx,\[0+eax+8\]						;leal	0(,%eax,8), %ebx
MOV     ecx,\[ebp+12\]						;movl	12(%ebp), %ecx
MOV     eax,\[ebp-32\]						;movl	-32(%ebp), %eax
MOV     edx,\[ebp-28\]						;movl	-28(%ebp), %edx
MOV     \[ecx+ebx\],eax						;movl	%eax, (%ecx,%ebx)
MOV     \[4+ecx+ebx\],edx						;movl	%edx, 4(%ecx,%ebx)
LEA		eax,\[ebp-12\]						;leal	-12(%ebp), %eax
INC  	dword \[eax\]							    ;incl	(%eax)
JMP		L2									;jmp	    L2

L1:
ADD esp,28 ;addl $28, %esp
POP ebx ;popl %ebx
POP ebp ;popl %ebp
RET ;ret
;.ident "GCC: (GNU) 3.2.3"

[ZoogieZork]

Sirrius wrote:

LEA ebx,[0+eax+8] ;leal 0(,%eax,8),%ebx

Careful! The AT&T syntax for memory refs is:

displacement(base,index,scale)

Which translates to:

[base+(index*scale)+displacement]

So the above line should be:

lea ebx,[eax*8]

That's just the first thing I noticed (and it's used in a number of places). - Mike

[Sirrius]

How about these conversions, are they okay? LEA edx,[eax+edx] ;leal (%eax,%edx), %edx LEA eax,[ebp-12] ;leal -12(%ebp), %eax INC eax ;incl (%eax) MOV dword [ebp-12],0 ;movl $0, -12(%ebp)