Member Avatar for avarionist

Lods byte ptr ds:[esi] ;i know that it loads a byte that is a pointer my question is " is the pointer ds with esi as an offset or is it the other way around or am i just plain wrong" ?

Edited by avarionist because: n/a
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Member Avatar for Ancient Dragon

esi just contains an address that is within the ds segment. ds is not a pointer -- it contains the address of the data segment. Sometimes you might even see cs:[esi] or even ss:[esi] in which case esi is pointer to somewhere in the code segment or stack segment, respectively.

Member Avatar for avarionist

esi just contains an address that is within the ds segment. ds is not a pointer -- it contains the address of the data segment. Sometimes you might even see cs:[esi] or even ss:[esi] in which case esi is pointer to somewhere in the code segment or stack segment, respectively.

thanks AncientDragon :) you have all the answers :D

Member Avatar for wildgoose

The default for a [si] [esi] [rsi] access is the ds: Data segment / selector. But it can be overriden with an alternate such as AncientDragon indicated
cs: Code Segment/Selector,
es:Extra Segment/Selector,
ss: Stack Segment/Selector
fs, gs Selectors

Another item to note is LODS also increments the index by the size of the data referenced!

Assuming 32-bit Protected Mode

lodsb
   mov al,ds:[esi]
   add esi,1
lodsw
   mov ax,ds:[esi]
   add esi,2
lodsd
   mov eax,ds:[esi]
   add esi,4

You can use the Repeat instruction rep

rep lodsd
L1: mov eax,ds:[esi]
   add esi,4
   dec ecx
   jne L1
Member Avatar for avarionist

The default for a [si] [esi] [rsi] access is the ds: Data segment / selector. But it can be overriden with an alternate such as AncientDragon indicated
cs: Code Segment/Selector,
es:Extra Segment/Selector,
ss: Stack Segment/Selector
fs, gs Selectors

Another item to note is LODS also increments the index by the size of the data referenced!

Assuming 32-bit Protected Mode

lodsb
   mov al,ds:[esi]
   add esi,1
lodsw
   mov ax,ds:[esi]
   add esi,2
lodsd
   mov eax,ds:[esi]
   add esi,4

You can use the Repeat instruction rep

rep lodsd
L1: mov eax,ds:[esi]
   add esi,4
   dec ecx
   jne L1

Thanks for the info lods is an instruction i rarely see let alone use :)

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