Re: [9fans] which register is used as FP on the x86

[Latchesar Ionkov <lucho@ionkov.net>]

The Plan9 calling convention doesn't use BP as frame pointer.

	Lucho

PS. gcc -fomit-frame-pointer doesn't guarantee that no frame pointers will be
generated.

On Sat, Jun 26, 2004 at 01:56:04PM +0200, Andrew Lynch said:
> On Jun 25,  6:53pm, rog@vitanuova.com wrote:
> > no register is dedicated as a frame pointer.
> >
> > if you know the PC, you can find out the FP from the SP.
> 
> Maybe not dedicated, in the sense that you can also use it for other stuff, but
> the EBP register is intended to be used as FP:
> 
> "3. Stack-Frame Base Pointer (EBP) Register: The EBP register typically is used
> to access data structures passed on the stack. [...] If the stack pointer is
> copied into the base pointer before anything is pushed on the stack, the base
> pointer can be used to reference data structures with fixed offsets. [...]
> Instructions, such as ENTER and LEAVE instructions, are provided which
> automatically set up the EBP register for convenient access to variables."
> 
> intel 386DX Microprocessor Programmer's Reference Manual 1990
> 
> Andrew.
> 
> P.S. If you have a gcc targeted for x86 you can see for yourself by comparing
> the output of "gcc -S" with "gcc -fomit-frame-pointer -S".