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Re: Bug in x86-64 psABI or in gcc?
On Wed, Dec 9, 2009 at 7:10 AM, Andrew Haley <aph@redhat.com> wrote:
> H. Peter Anvin wrote:
>> On 12/09/2009 06:56 AM, Michael Matz wrote:
>>>> Aren't bits in the _Bool byte of"bar" specified by the psABI
>>> Right now they are specified in the psABI, you suggested to remove that
>>> specification.
>>>
>>
>> The intent of H.J.'s proposal is to require bits <7:1> == 0 in all cases
>> (and higher bits as don't cares, the same way a char is passed), as
>> opposed to the current text which requires <63:1> == 0 when passed as
>> registers or on the stack (and <7:1> == 0 when stored in a memory
>> object.) ?Furthermore, the current psABI text is inconsistent for
>> arguments are return values; this is a bug in the wordsmithing of the
>> text rather than intentional, if I remember the original discussions
>> correctly.
>
> Surely Postel's Law applies:
>
> ?Be conservative in what you do; be liberal in what you accept from others.
>
> So, return values should be zero-extended to the full word, but we shouldn't
> assume that parameters will be.
>
I guess you missed the discussion around July 2007:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42324#c5
--
H.J.