From: Uros Bizjak <ubizjak@gmail.com>
To: Alexander Monakov <amonakov@ispras.ru>
Cc: Jakub Jelinek <jakub@redhat.com>, X86 ML <x86@kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
GCC Development <gcc@gcc.gnu.org>
Subject: Re: typeof and operands in named address spaces
Date: Thu, 5 Nov 2020 14:46:44 +0100 [thread overview]
Message-ID: <CAFULd4bcCeNYQLj13k-VPteMUA1_BpdRCOnG8uB3JPF-i8Mo4A@mail.gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.20.13.2011051631120.9902@monopod.intra.ispras.ru>
On Thu, Nov 5, 2020 at 2:39 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
> On Thu, 5 Nov 2020, Alexander Monakov via Gcc wrote:
>
> > On Thu, 5 Nov 2020, Uros Bizjak via Gcc wrote:
> >
> > > > No, this is not how LEA operates. It needs a memory input operand. The
> > > > above will report "operand type mismatch for 'lea'" error.
> > >
> > > The following will work:
> > >
> > > asm volatile ("lea (%1), %0" : "=r"(addr) : "r"((uintptr_t)&x));
> >
> > This is the same as a plain move though, and the cast to uintptr_t doesn't
> > do anything, you can simply pass "r"(&x) to the same effect.
> >
> > The main advantage of passing a "fake" memory location for use with lea is
> > avoiding base+offset computation outside the asm. If you're okay with one
> > extra register tied up by the asm, just pass the address to the asm directly:
> >
> > void foo(__seg_fs int *x)
> > {
> > asm("# %0 (%1)" :: "m"(x[1]), "r"(&x[1]));
> > asm("# %0 (%1)" :: "m"(x[0]), "r"(&x[0]));
> > }
>
> Actually, in the original context the asm ties up %rsi no matter what (because
> the operand must be in %rsi to make the call), so the code would just
> pass "S"(&var) for the call alternative and "m"(var) for the native instruction.
Or pass both, "m"(var), and
uintptr_t *p = (uintptr_t *)(uintptr_t) &var;
"m"(*p) alternatives, similar to what is done in the original patch.
The copy to %rsi can then be a part of the alternative assembly.
Uros.
next prev parent reply other threads:[~2020-11-05 13:46 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-04 18:31 Uros Bizjak
2020-11-05 7:26 ` Richard Biener
2020-11-05 8:56 ` Uros Bizjak
2020-11-05 9:36 ` Alexander Monakov
2020-11-05 10:33 ` Uros Bizjak
2020-11-05 11:38 ` Alexander Monakov
2020-11-05 12:00 ` Uros Bizjak
2020-11-05 12:14 ` Alexander Monakov
2020-11-05 12:24 ` Richard Biener
2020-11-05 12:32 ` Uros Bizjak
2020-11-05 12:35 ` Uros Bizjak
2020-11-05 13:22 ` Alexander Monakov
2020-11-05 13:39 ` Alexander Monakov
2020-11-05 13:46 ` Uros Bizjak [this message]
2020-11-05 12:26 ` Uros Bizjak
2020-11-05 15:27 ` Andy Lutomirski
2020-11-05 11:03 ` Uros Bizjak
2020-11-05 9:45 ` Richard Biener
2020-11-05 9:51 ` Jakub Jelinek
2020-11-09 12:47 ` Peter Zijlstra
2020-11-09 19:38 ` Segher Boessenkool
2020-11-09 19:50 ` Nick Desaulniers
2020-11-10 7:57 ` Peter Zijlstra
2020-11-10 18:42 ` Nick Desaulniers
2020-11-10 20:11 ` Peter Zijlstra
2020-11-12 0:40 ` Segher Boessenkool
2020-11-12 0:47 ` Segher Boessenkool
2020-11-10 7:52 ` Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAFULd4bcCeNYQLj13k-VPteMUA1_BpdRCOnG8uB3JPF-i8Mo4A@mail.gmail.com \
--to=ubizjak@gmail.com \
--cc=amonakov@ispras.ru \
--cc=gcc@gcc.gnu.org \
--cc=jakub@redhat.com \
--cc=luto@amacapital.net \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).