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Re: RFC: Add 32bit x86-64 support to binutils
On Fri, Dec 31, 2010 at 2:03 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Thu, Dec 30, 2010 at 01:42:05PM -0800, H. Peter Anvin wrote:
>> On 12/30/2010 11:57 AM, Jakub Jelinek wrote:
>> >>
>> >> Would be nice if LFS would be mandatory on the new ABI, thus
>> >> off_t being 64bits.
>> >
>> > And avoid ambiguous cases that x86-64 ABI has, e.g. whether
>> > caller or callee is responsible for sign/zero extension of arguments, to
>> > avoid the need to sign/zero extend twice, etc.
>> >
>>
>> Ehwhat? ?x86-64 is completely unambiguous on that point; the i386 one is
>> not.
>
> It is not, sadly, see http://gcc.gnu.org/PR46942
> From what I can see the psABI doesn't talk about it, GCC usually sign/zero
> extends on both sides (exception is 32-bit arguments into 64-bit isn't
> apparently sign/zero extended on the caller side when doing tail calls),
> from what I gathered LLVM expects the caller to sign/zero extend (which is
> incompatible with GCC tail calls then), not sure about ICC, and kernel
> probably expects for security reasons that the callee sign/zero extends.
>
> ? ? ? ?Jakub
>
I added
---
When a value of type signed/unsigned char or short is returned or passed
in a register or on the stack, it should be sign/zero extended to
signed/unsigned
int.
---
to hjl/extension branch at
http://git.kernel.org/?p=devel/binutils/hjl/x86-64-psabi.git;a=summary
--
H.J.