Re: [9fans] FP register usage in Plan9 assembler

[Giacomo Tesio <giacomo@tesio.it>]

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Thanks for the explainations!

I did read in the Pike's paper about the syntax name+offset(FP), but I did
understood that name had to be a symbol already defined, and I was looking
for it in the c code. Sorry for the noise!

This led me to another question, however: I've read before that the plan9
compilers use the stack for va_list, but here the assembler is using it
also for explicit parameters, right?

Is it correct to say that this means that the Plan9 compiler suite *never*
follows the sysV calling convention documented at section 3.2.3 of AMD64
ABI http://www.x86-64.org/documentation/abi.pdf and always pushes
parameters to the stack?


Giacomo



2016-02-01 23:48 GMT+01:00 <cinap_lenrek@felloff.net>:

> FP is a translated to a varying offset to SP depending on where in the
> program
> you are. arguments on the stack are padded to 8 bytes on amd64, the first
> argument
> is not passed on the stack on function entry, but passed in BP register
> (RARG is an
> alias for that), however the slot on the stack for first arg is still
> reserved
> so we have a save place to splill it. so 0(FP) is first function argument
> on the
> stack, 8(FP) second argument 16(FP) third ect...
>
> --
> cinap
>
>

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