RIG Configuration files

This directory contains YAML files that describe configurations for the Random Instruction Generator (RIG). If not told otherwise, the RIG will read default.yml.

Inheritance

Configurations can inherit from one another. There are two uses for this. Firstly, it allows us to define customised versions of a more standard configuration. For example, you might have a configuration that’s just like the normal one but with many more loop instructions.

Secondly, we allow a configuration to give a list of possible parent configurations from which it should inherit. This allows a generic test to make (weighted) picks from different base configurations.

The details of how to specify a list of parent configurations for are described with the inherits field below. Once these have been resolved, we resolve each parent configuration, merge those together and finally merge with any fields defined in the current file.

Since the values stored in the file are essentially just weights (defining non-normalized probability distributions), we merge configurations by multiplying the weights together pointwise. We call the final resulting configuration the elaborated configuration.

Schema

The valid keys for these YAML files are:

• gen-weights:

  A dictionary of weights, keyed by generator name. In the elaborated configuration, there must be a weight defined for each generator (in practice, this is ensured by listing a weight for each in base.yml).

  These weights select the generator to try when starting a snippet. Note that instruction weights are mostly independent of this choice: increasing the instruction weights for BEQ and BNE won’t affect the number of branches generated. The only exception to this rule is if the weights of all the instructions that the generator can use are zero. For example, setting the instruction weights for BEQ and BNE to zero will disable the branch generator.

• insn-weights:

  A dictionary of weights, keyed by instruction mnemonic. These are used by generators like StraightLineInsn to pick which straight line instruction to generate. To disable an instruction completely, set its weight to zero.

  These weights are also used by the special purpose generators. For example, the branch generator picks whether to use BEQ or BNE with weights from insn-weights.

• inherit:

  The most general form for this field is a list of dictionaries. Each dictionary represents a possible choice of parents and one is picked at elaboration time.

  Each dictionary must have a field called cfgs, which is a string giving a list of parent configurations separated by + signs. It may also have a field called weight giving the weight of the entry (defaulting to 1).

  As a shorthand, an entry in the list can be a string, in which case this string is interpreted as the cfgs field, with a weight of 1.

  As an even shorter shorthand, a one-item list whose only item is a string can be replaced by just that string.

• ranges:

  A dictionary of maximum or minimum values, keyed with names like max-FOO or min-FOO, respectively.

  Supported names:

  • max-loop-iters: Used by the Loop generator to constrain the maximum number of loop iterations that it will pick.
  • max-loop-tail-insns: Used by the Loop generator to constrain the maximum number of straight-line instructions it will generate as part of a loop’s tail.