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Re: Bug in x86-64 psABI or in gcc?
H.J. Lu wrote:
> 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
No, I didn't miss it. We have had discussions about this before.
I still think Postel's Law applies, particularly as we have an
explicit guarantee in the psABI that
---
When a value of type _Bool is passed in a register or on the stack,
the upper 63 bits of the eightbyte shall be zero.
---
Andrew.