Hints of ABI

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Erin 2023-10-22 18:43:44 +02:00
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spec.md
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@ -29,6 +29,8 @@
- Fl*n*: Floating point number of size *n* bits (Fl32, Fl64)
# Behaviour
- There is only one type of register, a general-purpose one.
Used for both integers and floats.
- Integer operations are wrapping, including signed numbers
- Bitshifts are truncating
- Two's complement
@ -464,3 +466,32 @@ Program counter stays on the currently executed instruction
| 0x75 | LDR16 | RRPH | LDR |
| 0x76 | STR16 | RRPH | STR |
| 0x77 | JMP16 | P | JMP |
# psABI
## C datatypes and alignment
- One byte is 8 bits
| C Type | Description | Byte sizes |
|:------------|:-------------------------|:-----------|
| char | Character / byte | 1 |
| short | SShort integer | 2 |
| int | Integer | 4 |
| long | Long integer | 8 |
| long long | Long long integer | 8 |
| float | Single-precision float | 4 |
| double | Double-precision float | 8 |
| long double | Extended-precision float | TBD |
## Call convention
- Registers r1 r30 are caller saved
- Registers r31 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 |
If return value is too big to fit one register, r2 is also used.
TODO: Stack pointer, Thread pointer, ...