Kernel ABI: Difference between revisions

← Older edit

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-Inputs are read from registers starting from r0 and outputs are written back to the same registers (also starting with r0).
+= Calling Convention =
+Seems to be [https://github.com/ARM-software/abi-aa/blob/main/aapcs32/aapcs32.rst#the-base-procedure-call-standard AAPCS]-based (with modifications)
+== Overview ==
+=== Inputs ===
+* <code>r0–r3</code> : Argument / Scratch registers (caller-saved), inherited from AAPCS. ''If an input is to be placed on the stack, it will instead use the next free register starting from <code>r0</code>.''
+=== Outputs ===
+* <code>r0-r1</code> : Result, inherited from AAPCS. ''If multiple outputs are returned (e.g., <code>ControlMemory</code>), they are placed in consecutive registers starting from <code>r0</code>.''
+== Example ==
+<code>Result ControlMemory(uintptr_t* out, uintptr_t addr0, uintptr_t addr1, size_t size, MemoryOperation operation, MemoryPermission permissions)</code>
+=== Inputs ===
+Following standard [https://github.com/ARM-software/abi-aa/blob/main/aapcs32/aapcs32.rst#the-base-procedure-call-standard AAPCS] register selection:
+; <code>r1</code> -> addr0
+; <code>r2</code> -> addr1
+; <code>r3</code> -> size
+As there are still more arguments, the next free registers are selected starting from <code>r0</code>
+; <code>r0</code> -> operation
+; <code>r4</code> -> permissions
+=== Outputs ===
+; <code>r0</code> -> Result
+; <code>r1</code> -> uintptr_t out
+== System calls ==
 {| class="wikitable" border="1"
 |-
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 | Timer handle, initial_low, interval_low, initial_high, interval_high
 | Result
+|-
+| 0x28
+| GetSystemTick
+| None
+|
+<code>r0</code>: <code>Low 32 bits of the tick count</code>
+<br><code>r1</code>: <code>High 32 bits of the tick count</code>
 |-
 | 0x2D