Re: [Pgubook-readers] Register name history & style

[Jonathan Bartlett]

> 1) There's not much documented on the origins of the register labels:
> (ie eax, ebp, ...).  You go into a little detail on the "e" addition,
> but not much on the origins of "ax, bp, ...".  I can't remember if
> Randall's HLA Book explains these, I do have the book with me but have
> yet to research this further.  Main reason I make mention, is I'm having
> a tough time remembering the register names! I figure if I knew the
> history, I may remember the names more easily. (maybe)

"A" stands for "accumulator", I believe.  It's kind of the default,
generic register.  In the 32-bit architecture, that's not as much of a
distinction, but in the 16-bit version, ax had more of a special role.
It's still special for multiplication and division.

"BP" is the "base pointer" also called the "frame pointer".  It is used to
have a constant location for the start of the stack frame at the beginning
of a function.  It's not technically needed -- you can also do offsets
from the stack pointer ESP.  However, often times during a function you
will want to push things onto the stack, and using EBP will keep you from
having to recalculate your offsets every time you do a stack operation.
gcc even has a compilation option to do this, I think it's
-fomit-frame-pointer.

"CX" is often used as a counter.

"SI" is the "string index" register -- it is often used for string
operations.

I'm not sure if BX or DX have any specific meanings, or if they were just
"alphabet fillers".

> 2) I noticed you didn't make much mention on the (spacing) style of your
> source assembly files.  Hate typing in source and trying to figure out
> if there's 2 spaces or what, although spacing doesn't make much
> difference.  C has a tool called "indent" that will alter the spacing
> according to the style choosen.  Anything similar for ASM?

I don't think there is an assembly language spacing guideline.  It's
mostly pretty flat anyway.

Jon