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Diffstat (limited to 'scripts/decodetree.py')
| -rwxr-xr-x | scripts/decodetree.py | 134 |
1 files changed, 1 insertions, 133 deletions
diff --git a/scripts/decodetree.py b/scripts/decodetree.py index e342d278b8..33e32ee87f 100755 --- a/scripts/decodetree.py +++ b/scripts/decodetree.py @@ -17,139 +17,7 @@ # # Generate a decoding tree from a specification file. -# -# The tree is built from instruction "patterns". A pattern may represent -# a single architectural instruction or a group of same, depending on what -# is convenient for further processing. -# -# Each pattern has "fixedbits" & "fixedmask", the combination of which -# describes the condition under which the pattern is matched: -# -# (insn & fixedmask) == fixedbits -# -# Each pattern may have "fields", which are extracted from the insn and -# passed along to the translator. Examples of such are registers, -# immediates, and sub-opcodes. -# -# In support of patterns, one may declare fields, argument sets, and -# formats, each of which may be re-used to simplify further definitions. -# -# *** Field syntax: -# -# field_def := '%' identifier ( unnamed_field )+ ( !function=identifier )? -# unnamed_field := number ':' ( 's' ) number -# -# For unnamed_field, the first number is the least-significant bit position of -# the field and the second number is the length of the field. If the 's' is -# present, the field is considered signed. If multiple unnamed_fields are -# present, they are concatenated. In this way one can define disjoint fields. -# -# If !function is specified, the concatenated result is passed through the -# named function, taking and returning an integral value. -# -# FIXME: the fields of the structure into which this result will be stored -# is restricted to "int". Which means that we cannot expand 64-bit items. -# -# Field examples: -# -# %disp 0:s16 -- sextract(i, 0, 16) -# %imm9 16:6 10:3 -- extract(i, 16, 6) << 3 | extract(i, 10, 3) -# %disp12 0:s1 1:1 2:10 -- sextract(i, 0, 1) << 11 -# | extract(i, 1, 1) << 10 -# | extract(i, 2, 10) -# %shimm8 5:s8 13:1 !function=expand_shimm8 -# -- expand_shimm8(sextract(i, 5, 8) << 1 -# | extract(i, 13, 1)) -# -# *** Argument set syntax: -# -# args_def := '&' identifier ( args_elt )+ ( !extern )? -# args_elt := identifier -# -# Each args_elt defines an argument within the argument set. -# Each argument set will be rendered as a C structure "arg_$name" -# with each of the fields being one of the member arguments. -# -# If !extern is specified, the backing structure is assumed to -# have been already declared, typically via a second decoder. -# -# Argument set examples: -# -# ®3 ra rb rc -# &loadstore reg base offset -# -# *** Format syntax: -# -# fmt_def := '@' identifier ( fmt_elt )+ -# fmt_elt := fixedbit_elt | field_elt | field_ref | args_ref -# fixedbit_elt := [01.-]+ -# field_elt := identifier ':' 's'? number -# field_ref := '%' identifier | identifier '=' '%' identifier -# args_ref := '&' identifier -# -# Defining a format is a handy way to avoid replicating groups of fields -# across many instruction patterns. -# -# A fixedbit_elt describes a contiguous sequence of bits that must -# be 1, 0, [.-] for don't care. The difference between '.' and '-' -# is that '.' means that the bit will be covered with a field or a -# final [01] from the pattern, and '-' means that the bit is really -# ignored by the cpu and will not be specified. -# -# A field_elt describes a simple field only given a width; the position of -# the field is implied by its position with respect to other fixedbit_elt -# and field_elt. -# -# If any fixedbit_elt or field_elt appear then all bits must be defined. -# Padding with a fixedbit_elt of all '.' is an easy way to accomplish that. -# -# A field_ref incorporates a field by reference. This is the only way to -# add a complex field to a format. A field may be renamed in the process -# via assignment to another identifier. This is intended to allow the -# same argument set be used with disjoint named fields. -# -# A single args_ref may specify an argument set to use for the format. -# The set of fields in the format must be a subset of the arguments in -# the argument set. If an argument set is not specified, one will be -# inferred from the set of fields. -# -# It is recommended, but not required, that all field_ref and args_ref -# appear at the end of the line, not interleaving with fixedbit_elf or -# field_elt. -# -# Format examples: -# -# @opr ...... ra:5 rb:5 ... 0 ....... rc:5 -# @opi ...... ra:5 lit:8 1 ....... rc:5 -# -# *** Pattern syntax: -# -# pat_def := identifier ( pat_elt )+ -# pat_elt := fixedbit_elt | field_elt | field_ref -# | args_ref | fmt_ref | const_elt -# fmt_ref := '@' identifier -# const_elt := identifier '=' number -# -# The fixedbit_elt and field_elt specifiers are unchanged from formats. -# A pattern that does not specify a named format will have one inferred -# from a referenced argument set (if present) and the set of fields. -# -# 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. -# -# The decoder will call a translator function for each pattern matched. -# -# Pattern examples: -# -# addl_r 010000 ..... ..... .... 0000000 ..... @opr -# addl_i 010000 ..... ..... .... 0000000 ..... @opi -# -# which will, in part, invoke -# -# trans_addl_r(ctx, &arg_opr, insn) -# and -# trans_addl_i(ctx, &arg_opi, insn) +# See the syntax and semantics in docs/devel/decodetree.rst. # import os |