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2017-05-01 Engineering Notes for XED

The files.cfg files specify which files get collected in to the
"obj/dgen" directory and then used for the subsequent build.  Each
files.cfg file has lines in token:value format specifying the tokens
below. The values are generally file names. Some of the tokens also
have priority values used for replacing earlier files.

dec-spine:

   the top level sequence of actions for decoding. This is the ISA()
   nonterminal.

dec-instructions:

   instruction patterns used to create the decoder. Each instruction
   is defined in in a sequence of token:value lines between a pair of
   lines containing curly braces { ... }.  Some of the tokens are
   repeatable, some are not. The most common tokens are:


   These tokens are not repeatable:
   
     ICLASS      : instruction name
     
     DISASM      : (optional) substituted name when a simple conversion
                   from iclass is inappropriate
     
     ATTRIBUTES  : (optional) names for bits in the binary attributes field
     
     UNAME       : (optional) unique name used for deleting / replacing
                   instructions.
                   
     CPL         : current privilege level. Valid values: 0, 3.
     
     CATEGORY    : ad-hoc categorization of instructions
     
     EXTENSION   : ad-hoc grouping of instructions.  If no ISA_SET is
                   specified, this is used instead.
                   
     ISA_SET     : (optional) name for the group of instructions that
                   introduced this feature. On the older stuff we used the
                   EXTENSION field but that got too complicated.
                   
     FLAGS       : (optional) read/written flag bit values.
     
     COMMENT     : (optional) a hopefully useful comment

   These are repeatable:
     
     PATTERN     : the sequence of bits and nonterminals used to
                   decode/encode an instruction.
                   
     OPERANDS    : the operands, typicall registers,  memory operands
                   and pseudo-resources.
                   
     IFORM       : (optional) a name for the pattern that starts with the
                   iclass and bakes in the operands. If omitted, xed
                   tries to generate one. We often add custom suffixes
                   to these to disambiguate certain combinations.

   The PATTERN and OPERANDS lines come in pairs. Each pair can have
   its own IFORM line.
   
   The PATTERN and OPERANDS tokens require further description due to
   their complexity and importance.

    
enc-instructions:

   instruction patterns used to create the encoder. Same forat as
   dec-instructions. We an include extra instructions for encoding
   standardized wide nops for example.
   
dec-patterns:

   non-instruction patterns and tables used to create the decoder

enc-patterns:

   non-instruction patterns and tables used to create the encoder.
   
enc-dec-patterns:

   decode patterns used for encode
   
fields:

   names and properties of storage variables. This is where the
   decoder and the encoder store all dynamicly collected and derived
   information about instructions.

state:

   This rathr poorly named file contains simple macro definitions to
   abstract and name some of the details of the conventions.  Example:
   (1) Rather than say "MODE=2" we can say "mode64". (2) Rather than
   say "MODE!=2" we can say "not64".

registers:

   Register name definition. Includes type, width, nesting
   information, and ordinal name.

widths:

   The operands have types and widths. The width system gives names to
   these features. Operand widths often vary with the x86 effective
   operand size calculation; This is where those widths are specified.
   A width is called and "oc2-code" and maps to a lower level type called
   an "xtype" and a set of one or more widths. The name "oc2-code" comes
   from the old Intel SDM opcode maps that tried to use two letters to
   specify operand widths but that system was incomplete.

element-types:

   This maps xtypes to base-types (UINT, INT, SINGLE, DOUBLE, etc.)
   and bit widths.
        
element-type-base:

    Enumeration definition file for the
    xed_operand_element_type_enum_t base type enumeration.

extra-widths:

   In the early XED instruction descriptions, we omitted the oc2-code
   for the nonterminals for register values. This table supplies
   default oc2-values (widths, see above) for the older undecorated
   register nonterminals.

pointer-names:

   For printing memory operations in disassembly, we are required to
   map memory reference widths to terms like "WORD" or "DWORD"
   etc. This file establishes that mapping.
 
    
chip-models:

   XED defines a xed_chip_enum_t as a collection of xed_isa_set_enum_t
   values. This file defines that mapping. Most xed chips are based on
   earlier chips and include all their features by specifying
   ALL_OF(x) where x is some earlier chip.  It is also possible to
   remove features with NOT(y) but that is not used very frequently.


conversion-table:

   string tables for converting field values to ASCII strings during
   disassembly.
  
ild-scanners:

   Since XED supports variance in what features are enabled, the
   instruction-length-decoder (ILD) allows overriding what scanners
   are baked in ot the build. This file supplies the C code function
   xed_ild_scanners_init() which is responsible for wiring up the ILD
   scanners in the correct order.
   
ild-getters:

   Not currently used.  Allows extending the list of
   xed3_operand_get_*() functions with functions that are used during
   decoding for creating hash values.  These functions are generally
   only used in prototyping and internal early enabling before the
   features or the code supporting those features are made exposed
   publicly. Once the features defined here become pulic, the code can
   be moved to the static part of the code.

   
cpuid:

   Maps xed_isa_set_enum_t values to a set of CPUID bits. Each
   instruction pattern belongs to one xd_isa_set_enum_t value.
