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Changed psABI spec

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Erin 2023-11-15 12:45:40 +01:00
parent 68094ce0ae
commit 569f154bcc
1 changed files with 19 additions and 11 deletions
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spec.md
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@ -480,18 +480,26 @@ Program counter stays on the currently executed instruction
| long long | Long long integer | 8 |
| float | Single-precision float | 4 |
| double | Double-precision float | 8 |
| long double | Extended-precision float | TBD |
| long double | Extended-precision float | 8 |
- Bikeshedding note: `long double` is now 8 bytes as
the base ISA does not support `f128`. an extension
for that should be made.
## Call convention
- Registers r1 – r30 are caller saved
- Registers r31 – r255 are callee saved
- Registers r1 – r31 are caller saved
- Registers r32 – r255 are callee saved
| Register | Description | Saver |
|:---------|:--------------------|:-------|
| r0 | Hard-wired zero | N/A |
| r1 - r2 | Return values | Caller |
| r2 - r11 | Function parameters | Caller |
| r30 | Return address | Caller |
| Register | Description | Saver |
|:-----------|:--------------------|:-------|
| r0 | Hard-wired zero | N/A |
| r1 - r2 | Return values | Caller |
| r2 - r11 | Function parameters | Caller |
| r12 - r30 | General purpose | Caller |
| r31 | Return address | Caller |
| r32 - r253 | General purpose | Callee |
| r254 | Stack pointer | Callee |
| r255 | Thread pointer | N/A |
If return value is too big to fit one register, r2 is also used.
TODO: Stack pointer, Thread pointer, ...
- If return value is too big to fit r1, r2 is also used.
- Values larger than two double-words are passed by reference