This page contains documentation for the implementation of qBeta for the ARM processor as in Apple Silicon.
Status
As of sept 22, 2026 some of the basic mechanisms have ben implemented:
- Binary and unaryiary expressions
- Invocation/instantiation of patterns
Inner- i
f:then, if:then:else, leaveandrestartin local block (OD) - Arrays (repetitions), String arrays
- Assignment of primitive values and references
- Parameters being primitive values and references
The following issues need to be handled:
- Temporary data-items for complex expressions
- May run out of registers
- Invocations/instantiations during evaluation of actual parameters
- Perhaps invocations during store of parameters
- Leave/restart out of blocks
- Coroutines
- Value objects
- Floating point data-items
- Garbage collection
- Object layout and extension of the ODtemplate, see below
- Errors and unknown issues;-)
Object layout
Currently all objects have the following layout:
| 0/0: | return register – lr |
| 1/8: | caller object – x28 |
| 2/16: | pointer to VDT_table |
| 3/24: | not used |
| 4/32: | Data-item 1 |
| 5/40: | Data-item 2 |
| 6/48: | Data-item 3 |
| … | … |
VDT-table
Currently the ObjectDescriptor-template (ODtemplate) is simple; it has the name of the pattern/OD and the virtuals bindings of the OD
| 0: | offSet to asciiz string |
| 8: | pointer to code for virtual binding |
| 16: | … |
| … | |
| asciiz string | Name of pattern/OD |
The VDT-table must be extended to a full OD-template with additional information
- Size of the objects – perhaps
- Pointer to OD-template for super
- Garbage collection info
- The kind of the objects: plain, indexed (array), ObjStructure (for pattern variables)
Future object kinds
We currently work on marking the various ODs depending on what they are used for:
| isData | Used as a type for a data-item |
| isOnlyData | isData and no statements |
| hasParams | has in / out parameters |
| isLocalExe | has statements but on invocations |
| hasAllocCode | has data-items that need alloc code |
| isCoroutine | a coroutine object that mya be suspend and resumed |
| codeExists | hasParams or hasAllocCode or isLocalExe or isCoroutine |
The above markings may overlap.
We may need to add a property identifying a method:
- not isData and not isOnlyData and not isCoroutine [and codeExists ? ]
Register usage
The table below shows the usage of registers
| stack pointer – not used by qBeta | x31 |
| link register – lr | x30 |
| HeapTop – HT ARM conventions is frame pointer | x29 |
| thisObj | x28 |
| references used for passing reference parameters | x15, x16, … x26 |
| values used for passing primitive value parameters | x0, x1, … x14 |
The ARM convention is that x19-x28 are callee-saved registers
All other registers may be modified by a given callee
We do not adhere to the ARM conventions.
We may have to adjust to some of the conventions, perhaps have HT as a calle-saved register.