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: Thu, 12 Jan 2023 01:28:45 +0000 (GMT) [thread overview]
Message-ID: <alpine.DEB.2.21.2301120116310.65308@angie.orcam.me.uk> (raw)
In-Reply-To: <f68e897d-d64f-22cc-1ac2-6b49fa4c148d@suse.com>
On Wed, 11 Jan 2023, Jan Beulich wrote:
> > 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?
>
> The parsing of an 'a' type operand involves expression(), a side effect of
> which is to insert a symbol table entry for symbols not otherwise
> recognized (and note how my_getSmallExpression() addresses the same issue
> by filtering out GPR names first [1]). Yes, in a way this is an
> "insufficient undoing" issue, just that undoing of that symbol table
> insertion would be quite hard and/or fragile (from all I can tell). And
> this is where the dual meaning of symbol names comes into play: This looks
> to be intentional, and hence we can't make use of md_parse_name() to
> suppress the symbol table insertion in the first place for symbols which
> (in other contexts) identify registers.
Thank you for looking into it. Indeed it looks to me like a problem with
`expression' (or `expr' really) and the way the RISC-V assembly dialect
defines register references (unlike the MIPS one which uses a `$' prefix).
At a glance it seems to me that the correct approach would be to define a
"dry run" mode for `expr' and use it in the RISC-V backend to validate an
operand in the first invocation without causing any side effects, and then
only once all the operands have been processed and an opcode table entry
accepted `expr' would be called to finalise the expression.
I realise it's something you may not be willing to commit to, as it's
likely a larger task than a random tweak to the RISC-V backend, but I
think it's the way we ought to do it rather than piling up workarounds.
FWIW,
Maciej
next prev parent reply other threads:[~2023-01-12 1:28 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
2023-01-11 9:28 ` Jan Beulich
2023-01-12 1:28 ` Maciej W. Rozycki [this message]
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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