Re: [PATCH] aarch64: Fix the documentation on :pg_hi21:

[Yufeng Zhang <Yufeng dot Zhang at arm dot com>]

On 05/29/14 13:19, Yufeng Zhang wrote:
> Hi Martin,
>
> On 05/29/14 13:00, Martin Storsjo wrote:
> > The syntax described, including a leading '#', was not supported
> > in practice. (For :lo12: it is optional.)
>
> I believe this is an issue in the parser; '#' should be optional in
> either case.
>
> It looks like gas/config/tc-aarch64.c:parse_adrp () is missing the
> skip_past_char (&p, '#') at its beginning; see parse_half () for an example.

After spending some time this afternoon reading ARMv8 Architecture 
Reference Manual (ARMARM) and having a discussion with a colleague, I 
think I'll have to take back what I just said.  Sorry!

The A64 assembly language allows the optional # character to introduce 
constant immediate operands, e.g. in LDR instructions with immediate offset:

  LDR <Wt>, [<Xn|SP>], #<simm>

and in the bitfield move instructions:

  BFM <Wd>, <Wn>, #<immr>, #<imms>

The ADRP instruction, however, has the following syntax:

  ADRP <Xd>, <label>

whose second operand is a program label whose 4KB page address is to be 
calculated, and for such a operand, it doesn't make much sense to allow 
the # character as an optional prefix, e.g. ADRP X0, #foo would look 
weird and confusing.

So I think your original patch is the right one to go with, and my only 
comment is to remove both # characters from the line of

"
  @samp{#:pg_hi21:} and @samp{#:lo12:} respectively.
"

Apologize again for the previous wrong direction.

Please get an approval from Marcus.

Thanks,
Yufeng


> Yufeng
>
> > ---
> >    gas/doc/c-aarch64.texi | 10 +++++-----
> >    1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/gas/doc/c-aarch64.texi b/gas/doc/c-aarch64.texi
> > index cce4f61..1f4ce4c 100644
> > --- a/gas/doc/c-aarch64.texi
> > +++ b/gas/doc/c-aarch64.texi
> > @@ -186,24 +186,24 @@ For example to load the 48-bit absolute address of @var{foo} into x0:
> >    @cindex ADRP, ADD, LDR/STR group relocations, AArch64
> >    Relocations for @samp{ADRP}, and @samp{ADD}, @samp{LDR} or @samp{STR}
> >    instructions can be generated by prefixing the label with
> > -@samp{#:pg_hi21:} and @samp{#:lo12:} respectively.
> > +@samp{:pg_hi21:} and @samp{#:lo12:} respectively.
> >
> >    For example to use 33-bit (+/-4GB) pc-relative addressing to
> >    load the address of @var{foo} into x0:
> >
> >    @smallexample
> > -        adrp x0, #:pg_hi21:foo
> > +        adrp x0, :pg_hi21:foo
> >            add  x0, x0, #:lo12:foo
> >    @end smallexample
> >
> >    Or to load the value of @var{foo} into x0:
> >
> >    @smallexample
> > -        adrp x0, #:pg_hi21:foo
> > +        adrp x0, :pg_hi21:foo
> >            ldr  x0, [x0, #:lo12:foo]
> >    @end smallexample
> >
> > -Note that @samp{#:pg_hi21:} is optional.
> > +Note that @samp{:pg_hi21:} is optional.
> >
> >    @smallexample
> >            adrp x0, foo
> > @@ -212,7 +212,7 @@ Note that @samp{#:pg_hi21:} is optional.
> >    is equivalent to
> >
> >    @smallexample
> > -        adrp x0, #:pg_hi21:foo
> > +        adrp x0, :pg_hi21:foo
> >    @end smallexample
> >
> >    @node AArch64 Floating Point