On Thu, Feb 25, 2021, at 10:57 AM, Maciej W. Rozycki wrote:
> On Thu, 25 Feb 2021, Jiaxun Yang wrote:
>
> > > There is a far easier way to do this, which is to just emit an assembler
> > > macro, and let the assembler generate the labels and relocs. This is what
> > > the RISC-V GCC port does by default. This prevents some optimizations
> > > like
> > > scheduling the two instructions, but enables some other optimizations like
> > > loop unrolling. So it is a tossup. Sometimes we get better code with the
> > > assembler macro, and sometimes we get better code by emitting the auipc
> > > and
> > > addi separately.
> >
> > Thanks all,
> >
> > I'll take this approach first, add "lla, dlla" pseudo-instructions to
> > assembler and seeking optimization
> > in future.
>
> The DLA and LA macros are supposed to do that already, no need to invent
> new names.
Hmm, how could we tell if the symbol is local?
Global symbols still needs to be load from GOT.
I saw RISC-V dealt that by “lla” pesudo-op which indicate the symbol is local.
>
> They may not have been implemented for R6, but I'm not sure. There was
> some resistance against macros at one point as the new generation came to
> work on the MIPS assembler and consequently inconsistencies resulted in
> the language that may not have b"en removed to date.
>
> In any case you need to use `-mno-explicit-relocs' with GCC then so as
> not to break the compiler's semantics or assumptions.
>
> > Btw I found we don't have any document for MIPS pseudo-instructions. RISC-V
> > put them in ISA manual
> > but it is not the case for MIPS. Is it possible to have one in binutils?
>
> There are MIPS assembly language books available; I'm fairly sure Dominic
> Sweetman's "See MIPS Run" has a chapter (I don't have the book at hand).
> I don't think GNU binutils documentation is supposed to describe the
> assembly dialects supported, except maybe for GNU extensions (pseudo-ops).
Yeah I saw See MIPS Run, but it's not a mandatory specification.
Without a specification we may have different implementation across toolchains
and trouble users.
Thanks.
- Jiaxun
>
> Maciej
>
--
- Jiaxun
