From: Dave Brolley <brolley@redhat.com>
To: Ronald Hecht <ronald.hecht@uni-rostock.de>
Cc: cgen@sourceware.org
Subject: Re: Simulator: base_insn and insn in decode.c
Date: Thu, 03 Aug 2006 21:55:00 -0000 [thread overview]
Message-ID: <44D270CF.30506@redhat.com> (raw)
In-Reply-To: <44CDF0AC.6070707@uni-rostock.de>
Ronald Hecht wrote:
> Hello again,
>
> i found another problem in decode. c. As I have variable instruction
> size, decode.c does not handle base_insn and insn in the right way.
> The file looks like this:
>
> const IDESC *
> proc8bf_decode (SIM_CPU *current_cpu, IADDR pc,
> CGEN_INSN_INT base_insn, CGEN_INSN_INT entire_insn,
> ARGBUF *abuf)
> {
> /* Result of decoder. */
> PROC8BF_INSN_TYPE itype;
>
> {
> CGEN_INSN_INT insn = base_insn;
>
> {
> unsigned int val = (((insn >> 0) & (63 << 0)));
> switch (val)
> {
> case 0 :
> if ((entire_insn & 0xff) == 0x0)
> { itype = PROC8BF_INSN_NOP; goto extract_sfmt_nop; }
> itype = PROC8BF_INSN_X_INVALID; goto extract_sfmt_empty;
The generated decoder expects base_insn to be the first base-insn-size
bits of the insn shifted as far right as possible. What you have
specified is correct and the (((insn >> 0) & (63 << 0))) test us
correct. It is looking at the low order 6 bits of the base_insn which
are the only significant ones (according to your cpu file.
The generated decoder expects entire_insn to the all of the insn bits,
also shifted as far right as possible.
The test around the goto is intended to make sure that the untested
base_insn bits are as expected. It needs to be there, otherwise, invalid
insns get recognized as valid ones. However, it would seem that the test
should be against base_insn and not against entire_insn. I'll have a
look at some other cgen simulators, including those which use SID to
make sure that this assertion holds water. It probably hasn't come up
until now, since most sims I have seen are able to pass the same value
for base_insn and entire_insn.
Dave
next prev parent reply other threads:[~2006-08-03 21:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-31 11:58 Ronald Hecht
2006-08-03 21:55 ` Dave Brolley [this message]
2006-08-03 22:08 ` Dave Brolley
2006-08-07 14:39 ` Ronald Hecht
2006-08-07 14:53 ` Ronald Hecht
2006-08-14 21:19 ` Dave Brolley
2006-08-15 8:39 ` Ronald Hecht
2006-08-04 8:51 ` Ronald Hecht
2006-08-14 20:34 ` Dave Brolley
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