From: "Maciej W. Rozycki" <macro@orcam.me.uk>
To: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Waterman <andrew@sifive.com>,
Jim Wilson <jim.wilson.gcc@gmail.com>,
nelson@rivosinc.com, Nick Clifton <nickc@redhat.com>,
binutils@sourceware.org, Palmer Dabbelt <palmer@dabbelt.com>
Subject: Re: [PATCH] gas/RISC-V: adjust assembler for opcode table re-ordering
Date: Tue, 10 Jan 2023 22:58:03 +0000 (GMT) [thread overview]
Message-ID: <alpine.DEB.2.21.2301102247420.65308@angie.orcam.me.uk> (raw)
In-Reply-To: <4a67f41c-3473-3833-c0fc-ed4f69a062e9@suse.com>
On Tue, 10 Jan 2023, Jan Beulich wrote:
> >> Thanks for fixing this. I don't have any issues with what's there, but looks
> >> like I'm also getting some failures (glibc/multilib errno related stuff). I'm
> >> trying to bisect those so I can't really get a proper test up now, I'll try to
> >> do so ASAP as it's really late to have stuff broken.
> >
> > I wonder why the RISC-V port needs such a hack while the MIPS one
> > doesn't.
>
> Perhaps I misunderstood your earlier reply then. There you said you deal with
> this by carefully ordering the opcode table. Here restoring the original order
> would only be a temporary workaround, as it would re-introduce the
> disassembler issue that was fixed by altering the order: Alias entries need to
> come ahead of "real" ones, or else respective alias mnemonics would never be
> emitted by the disassembler.
Correct. But why does it require such an intervention on the GAS side?
AFAIK similarly to the MIPS port and like the disassembler GAS tries to
match instructions in the order they appear in the opcode table, except
that the disassembler matches by the opcode/mask, but GAS matches by the
mnemonic/operands. It is expected that a single-operand alias appears
first so that the disassembler matches it first (unless `-M no-aliases'),
but it is also expected not to match a two-operand assembly instruction,
so that GAS proceeds to the next candidate opcode table entry.
And it does appear to happen, because correct machine code is produced
regardless of your hack, except for the spurious symbol produced. So is
it not the case that simply the state (interal relocations recorded) is
not correctly reset on an unsuccessful operand match? Why does it have to
be special-cased just for the `a' operand type?
Maciej
next prev parent reply other threads:[~2023-01-10 22:58 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-06 12:34 Jan Beulich
2023-01-07 23:29 ` Aurelien Jarno
2023-01-09 17:07 ` Jan Beulich
2023-01-09 19:07 ` Palmer Dabbelt
2023-01-09 21:59 ` Maciej W. Rozycki
2023-01-10 9:25 ` Jan Beulich
2023-01-10 22:58 ` Maciej W. Rozycki [this message]
2023-01-11 9:28 ` Jan Beulich
2023-01-12 1:28 ` Maciej W. Rozycki
2023-01-12 8:26 ` Jan Beulich
2023-01-12 8:40 ` Andrew Waterman
2023-01-10 12:31 ` Nick Clifton
2023-01-10 20:14 ` Palmer Dabbelt
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