Differences from ASL version 1.0 beta 7

[alastairreid]

ASLi aims to be a faithful implementation of ASL version 1.0 beta 7.

Unfortunately, the document DDI0612-asl_spec-00bet7 is no longer available from Arm's website so we cannot refer you to it. However beta 7 roughly corresponds to the state of ASLRef documentation around September 2024.

We know of the following differences between ASLi and ASL version 1.0 beta 7.

Missing features

The following features are missing

• The standard library print function can only take one argument ((Semi)Planned extension: "printf" #30
• Subtypes
• '<=' and '>=' patterns
• '.item0'/'.item1'/... syntax to extract fields from tuples
• 'pass' statements
• 'case' labels must be literal constants instead of constant expressions
• 'x DIV y' should report an error if 'y' is not an exact divisor of 'x'.

Extensions

We support the following extensions

• Optional exception markers: Functions that may throw an exception are marked with '?' and functions that always throw an exception are marked with '!'. Markers appear after the function name in both definitions and calls to the function.
• Bitvector literals can be written like this 32'xffff_ffff' where 32` is the bitwidth. (Literals can be written in hexadecimal (x), decimal (d) or binary (b).)
• It is not necessary to define a setter function when defining a getter function. This is useful for registers that should not be written directly.
• Records can have bitwidth parameters. This is useful when a record field is a bitvector whose size is not fixed.

Differences

• Constraints inferred for mutable local variables

  In ASL version 1.0 beta 7, the typechecker would infer the type "integer {0}" for mutable variable "x" in the following

  var x = 0;
  

  This would make sense for immutable variables since the only value x could have is 0. But, for a mutable variable, the inferred constraint would prevent the value being modified which is ... bizarre.

  ASLi fixes this issue by inferring the unconstrained type "integer". (More generally, ASLi always discards the constraint of the initializer in any mutable local variable declaration.)