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 > indirection.)
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. -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
