forked from AbleOS/holey-bytes
Hints of ABI
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spec.md
31
spec.md
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@ -29,6 +29,8 @@
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- Fl*n*: Floating point number of size *n* bits (Fl32, Fl64)
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# Behaviour
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- There is only one type of register, a general-purpose one.
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Used for both integers and floats.
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- Integer operations are wrapping, including signed numbers
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- Bitshifts are truncating
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- Two's complement
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@ -464,3 +466,32 @@ Program counter stays on the currently executed instruction
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| 0x75 | LDR16 | RRPH | LDR |
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| 0x76 | STR16 | RRPH | STR |
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| 0x77 | JMP16 | P | JMP |
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# psABI
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## C datatypes and alignment
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- One byte is 8 bits
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| C Type | Description | Byte sizes |
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|:------------|:-------------------------|:-----------|
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| char | Character / byte | 1 |
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| short | SShort integer | 2 |
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| int | Integer | 4 |
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| long | Long integer | 8 |
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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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## 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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| 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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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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