Re: [Nasm-devel] REG_C8REG

[Keith K. <sp...@dy...>]

>> ("mov eax,cr9" would compile in 32-bit mode, but
>> would actually generate "mov eax,cr1" for example.)
>
> The correct solution is to implement CR8D.
>
> See SF #1117594.
>
> That way, CR8...CR15 remain restricted to PM64
> while CR8D [*] remains restricted to non-PM64.
>
> [*] And up to CR15D of course, once someone is
>     shipping a CPU with those CRx, and decides
>     that LOCK makes them visible outside PM64.
>     Until then CR9D...CR15D shouldn't work.
>
> Why does this matter? Because of REX32 mode.
>
>                            <0> mode use32
>                            <0>
> 0000 0F20C0                <0>   mov eax,cr0
>                            <0> ; mov eax,cr8   ; requires REX for CR8
> 0003 F00F20C0              <0>   mov eax,cr8d
>                            <0>
>                            <0> ; mov rax,cr0   ; requires REX for RAX
>                            <0> ; mov rax,cr8   ; requires REX for RAX and
> CR8
>                            <0> ; mov rax,cr8d  ; requires REX for RAX
>                            <0>
>                            <0> mode rex32
>                            <0>
> 0007 0F20C0                <0>   mov eax,cr0
> 000A 440F20C0              <0>   mov eax,cr8
> 000E F00F20C0              <0>   mov eax,cr8d
>                            <0>
> 0012 480F20C0              <0>   mov rax,cr0
> 0016 4C0F20C0              <0>   mov rax,cr8
>                            <0> ; mov rax,cr8d  ; can't override default
> O64 to O32
>                            <0>
>                            <0> mode rex64
>                            <0>
>                            <0> ; mov eax,cr0   ; can't override default
> O64 to O32
>                            <0> ; mov eax,cr8   ; can't override default
> O64 to O32
>                            <0> ; mov eax,cr8d  ; can't override default
> O64 to O32
>                            <0>
> 001A 0F20C0                <0>   mov rax,cr0
> 001D 440F20C0              <0>   mov rax,cr8
>                            <0> ; mov rax,cr8d  ; can't override default
> O64 to O32
>

I'm sorry, but I have to totally reject that. There is no reason to make
such an explicit distinction when an implicit one will do.

I have this *funny* feeling that HPA will whole-heartedly agree.