forked from AbleOS/holey-bytes
Changed psABI spec
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spec.md
30
spec.md
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@ -480,18 +480,26 @@ Program counter stays on the currently executed instruction
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| long long | Long long integer | 8 |
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| float | Single-precision float | 4 |
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| double | Double-precision float | 8 |
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| long double | Extended-precision float | TBD |
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| long double | Extended-precision float | 8 |
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- Bikeshedding note: `long double` is now 8 bytes as
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the base ISA does not support `f128`. an extension
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for that should be made.
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## Call convention
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- Registers r1 – r30 are caller saved
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- Registers r31 – r255 are callee saved
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- Registers r1 – r31 are caller saved
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- Registers r32 – r255 are callee saved
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| Register | Description | Saver |
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|:---------|:--------------------|:-------|
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| r0 | Hard-wired zero | N/A |
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| r1 - r2 | Return values | Caller |
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| r2 - r11 | Function parameters | Caller |
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| r30 | Return address | Caller |
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| Register | Description | Saver |
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|:-----------|:--------------------|:-------|
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| r0 | Hard-wired zero | N/A |
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| r1 - r2 | Return values | Caller |
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| r2 - r11 | Function parameters | Caller |
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| r12 - r30 | General purpose | Caller |
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| r31 | Return address | Caller |
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| r32 - r253 | General purpose | Callee |
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| r254 | Stack pointer | Callee |
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| r255 | Thread pointer | N/A |
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If return value is too big to fit one register, r2 is also used.
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TODO: Stack pointer, Thread pointer, ...
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- If return value is too big to fit r1, r2 is also used.
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- Values larger than two double-words are passed by reference
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