H.J. Lu wrote: > On Wed, Dec 9, 2009 at 7:10 AM, Andrew Haley <a...@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.