Eax zeroed before call

Eax zeroed before call

[Peter McKinna]

Hi,

Hopefully this is the correct forum. I have a
Pascal like language using gcc as the backend.
For some reason a call to a simple procedure
with no parameters generates code to initialises eax to zero before the
call. With any parameters in the proc there’s no init.

Is there some way to prevent this init? Some
flag I can set, some arcane piece of wizardry?

Thanks Peter

Re: Eax zeroed before call

[Andrew Haley]

On 1/31/22 08:42, Peter McKinna via Gcc-help wrote:
> Hopefully this is the correct forum. I have a
> Pascal like language using gcc as the backend.
> For some reason a call to a simple procedure
> with no parameters generates code to initialises eax to zero before the
> call. With any parameters in the proc there’s no init.
> 
> Is there some way to prevent this init? Some
> flag I can set, some arcane piece of wizardry?

If your simple procedure doesn't have a prototype, EAX is initialized
to the number of arguments passed in vector registers, for compatibility
with old varargs functions.

I suggest you provide a prototype.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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