For RISC-V the opcode decode will change between different vendor
implementations of RISC-V (emulated by the same qemu binary).
Any two vendors may reuse the same opcode space, e.g., we may end up with:
# *** RV64 Custom-3 Extension ***
{
vt_maskc 0000000 ..... ..... 110 ..... 1111011 @r |has_xventanacondops_p
vt_maskcn 0000000 ..... ..... 111 ..... 1111011 @r |has_xventanacondops_p
someone_something ............ ..... 000 ..... 1100111 @i
|has_xsomeonesomething_p
}
With extensions being enabled either from the commandline
-cpu any,xventanacondops=true
or possibly even having a AMP in one emulation setup (e.g. application
cores having one extension and power-mangement cores having a
different one — or even a conflicting one).
Cheers,
Philipp.
On Mon, 10 Jan 2022 at 10:43, Philippe Mathieu-Daudé <[email protected]> wrote:
>
> Hi Philipp,
>
> On 1/9/22 21:56, Philipp Tomsich wrote:
> > This adds the possibility to specify a predicate-function that is
> > called as part of decoding in multi-patterns; it is intended for
> > use-cases (such as vendor-defined instructions in RISC-V) where the
> > same bitpattern may decode into different functions depending on the
> > overall configuration of the emulation target.
>
> But for a particular CPU, its "vendor ISAs" won't change at runtime.
>
> Since we know this at build time, I don't understand why you need
> predicate support at all.
>
> >
> > At this time, we only support predicates for multi-patterns.
> >
> > Signed-off-by: Philipp Tomsich <[email protected]>
> >
> > ---
> >
> > docs/devel/decodetree.rst | 7 ++++++-
> > scripts/decodetree.py | 24 +++++++++++++++++++++---
> > 2 files changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/docs/devel/decodetree.rst b/docs/devel/decodetree.rst
> > index 49ea50c2a7..241aaec8bb 100644
> > --- a/docs/devel/decodetree.rst
> > +++ b/docs/devel/decodetree.rst
> > @@ -144,9 +144,10 @@ Patterns
> > Syntax::
> >
> > pat_def := identifier ( pat_elt )+
> > - pat_elt := fixedbit_elt | field_elt | field_ref | args_ref |
> > fmt_ref | const_elt
> > + pat_elt := fixedbit_elt | field_elt | field_ref | args_ref |
> > fmt_ref | const_elt | predicate
> > fmt_ref := '@' identifier
> > const_elt := identifier '=' number
> > + predicate := '|' identifier
> >
> > The *fixedbit_elt* and *field_elt* specifiers are unchanged from formats.
> > A pattern that does not specify a named format will have one inferred
> > @@ -156,6 +157,10 @@ A *const_elt* allows a argument to be set to a
> > constant value. This may
> > come in handy when fields overlap between patterns and one has to
> > include the values in the *fixedbit_elt* instead.
> >
> > +A *predicate* allows to specify a predicate function (returing true or
> > +false) to determine the applicability of the pattern. Currently, this
> > +will change the decode-behaviour for overlapping multi-patterns only.
> > +
> > The decoder will call a translator function for each pattern matched.
> >
> > Pattern examples::
> > diff --git a/scripts/decodetree.py b/scripts/decodetree.py
> > index a03dc6b5e3..7da2282411 100644
> > --- a/scripts/decodetree.py
> > +++ b/scripts/decodetree.py
> > @@ -52,6 +52,7 @@
> > re_fld_ident = '%[a-zA-Z0-9_]*'
> > re_fmt_ident = '@[a-zA-Z0-9_]*'
> > re_pat_ident = '[a-zA-Z0-9_]*'
> > +re_predicate_ident = '\|[a-zA-Z_][a-zA-Z0-9_]*'
> >
> > def error_with_file(file, lineno, *args):
> > """Print an error message from file:line and args and exit."""
> > @@ -119,6 +120,14 @@ def whexC(val):
> > suffix = 'u'
> > return whex(val) + suffix
> >
> > +def predicate(val):
> > + """Return a string for calling a predicate function
> > + (if specified, accepting 'None' as an indication
> > + that no predicate is to be emitted) with the ctx
> > + as a parameter."""
> > + if (val == None):
> > + return ''
> > + return ' && ' + val + '(ctx)'
> >
> > def str_match_bits(bits, mask):
> > """Return a string pretty-printing BITS/MASK"""
> > @@ -340,7 +349,7 @@ def output_def(self):
> >
> > class General:
> > """Common code between instruction formats and instruction patterns"""
> > - def __init__(self, name, lineno, base, fixb, fixm, udfm, fldm, flds,
> > w):
> > + def __init__(self, name, lineno, base, fixb, fixm, udfm, fldm, flds,
> > w, p = None):
> > self.name = name
> > self.file = input_file
> > self.lineno = lineno
> > @@ -351,6 +360,7 @@ def __init__(self, name, lineno, base, fixb, fixm,
> > udfm, fldm, flds, w):
> > self.fieldmask = fldm
> > self.fields = flds
> > self.width = w
> > + self.predicate = p
> >
> > def __str__(self):
> > return self.name + ' ' + str_match_bits(self.fixedbits,
> > self.fixedmask)
> > @@ -499,7 +509,7 @@ def output_code(self, i, extracted, outerbits,
> > outermask):
> > if outermask != p.fixedmask:
> > innermask = p.fixedmask & ~outermask
> > innerbits = p.fixedbits & ~outermask
> > - output(ind, f'if ((insn & {whexC(innermask)}) ==
> > {whexC(innerbits)}) {{\n')
> > + output(ind, f'if ((insn & {whexC(innermask)}) ==
> > {whexC(innerbits)}{predicate(p.predicate)}) {{\n')
> > output(ind, f' /* {str_match_bits(p.fixedbits,
> > p.fixedmask)} */\n')
> > p.output_code(i + 4, extracted, p.fixedbits, p.fixedmask)
> > output(ind, '}\n')
> > @@ -826,6 +836,7 @@ def parse_generic(lineno, parent_pat, name, toks):
> > global re_fld_ident
> > global re_fmt_ident
> > global re_C_ident
> > + global re_predicate_ident
> > global insnwidth
> > global insnmask
> > global variablewidth
> > @@ -839,6 +850,7 @@ def parse_generic(lineno, parent_pat, name, toks):
> > flds = {}
> > arg = None
> > fmt = None
> > + predicate = None
> > for t in toks:
> > # '&Foo' gives a format an explicit argument set.
> > if re.fullmatch(re_arg_ident, t):
> > @@ -881,6 +893,12 @@ def parse_generic(lineno, parent_pat, name, toks):
> > flds = add_field(lineno, flds, fname, ConstField(value))
> > continue
> >
> > + # '|predicate' sets a predicate function to be called.
> > + if re.fullmatch(re_predicate_ident, t):
> > + tt = t[1:]
> > + predicate = tt;
> > + continue
> > +
> > # Pattern of 0s, 1s, dots and dashes indicate required zeros,
> > # required ones, or dont-cares.
> > if re.fullmatch('[01.-]+', t):
> > @@ -979,7 +997,7 @@ def parse_generic(lineno, parent_pat, name, toks):
> > if f not in flds.keys() and f not in fmt.fields.keys():
> > error(lineno, f'field {f} not initialized')
> > pat = Pattern(name, lineno, fmt, fixedbits, fixedmask,
> > - undefmask, fieldmask, flds, width)
> > + undefmask, fieldmask, flds, width, predicate)
> > parent_pat.pats.append(pat)
> > allpatterns.append(pat)
> >
