svn commit: r219079 - in head/sys/boot/i386: gptboot gptzfsboot
jhb at freebsd.org
Mon Feb 28 13:38:42 UTC 2011
On Saturday, February 26, 2011 10:04:00 pm Bruce Evans wrote:
> On Sun, 27 Feb 2011, Dimitry Andric wrote:
> > Log:
> > Clang's integrated assembler can now handle sys/boot/i386/boot2/sio.S.
> > It used to choke on the notation "inb (%dx),%al" for "inb %dx,%al"; GNU
> > as accepts both forms. Which notation is more 'correct' is an open
> > question. :)
> Nah, the former is just a syntax error since %dx is not dereferenced :-).
> It is a syntax error at the design level that parentheses are used for
> indirection. In better assembler syntaxes like Intel/Microsoft's one
> for x86 and Motorola's one for 6809, brackets are used for indirections
> so parentheses are not context-dependent. Then extra parentheses
> around expressions can have no effect. But dx isn't an expression,
> so (dx) should still be a syntax error. I think it is in I/M syntax
> but I can't test that easily. It is a syntax error in my x86/6809
> assembler. My assembler doesn't check, but emits a diagnostic for
> this :-). (My assembler wants brackets for indirection, but it has
> an option to to implement some bugs including use of parentheses for
OTOH, I actually prefer the ()'s. One could argue that I/O ports are simply
an alternate address space, and 'inb (%dx),%al' for more closely matches
'movb (%dx),%al' than something like 'movzb %dx,%al'. I find it even more
compelling for 'outb' as 'outb' clearly does not modify %dx, but %dx is an
address register, and addresses are in ()'s in x86 assembly.
In an assembly language where load and store are separate from inter-register
copies so that you have 'ld %r0,%r1', then I would be fine with the address
argument to inb/outb not using ()'s.
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