Differences

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--- spo600:aarch64_register_and_instruction_quick_start [2024/04/16 18:10] – external edit 127.0.0.1
+++ spo600:aarch64_register_and_instruction_quick_start [2025/02/19 16:54] (current) – [General-Purpose Integer Registers] chris
@@ Line 1: / Line 1: @@
 =====  AArch64 Register and Instruction Quick Start  =====
-This page contains very basic information on the AArch64 mode of the [[ARMv8]]/ARMv9 architecture: the [[Register|register]] layout and naming and some basic instructions. For more comprehensive information, see the references listed below.
+This page contains very basic information on the AArch64 mode of the [[ARMv8|ARMv8/ARMv9]] architecture: the [[Register|register]] layout and naming and some basic instructions. For more comprehensive information, see the references listed below.
 =====   Registers  =====
-====  General-Purpose Registers  ====
+====  General-Purpose Integer Registers  ====
 The aarch64 registers are named:
@@ Line 16: / Line 16: @@
   *  For all other instructions, it is a "zero" register, which returns 0 when read and discards data when written - named rzr (xzr, wzr)
-Usage during [[Syscalls|syscall]]/function call:
+Usage during [[Syscalls|syscall]] or [[procedure call]]:
-  *  **r0-r7 are used for integer and pointer arguments; additional arguments are on the stack. Return value is in r0 (if an integer or pointer)**
+  *  r0-r7 are used for integer and pointer arguments; additional arguments are on the stack. Return value is in r0 (if an integer or pointer)
-  *  **For syscalls, the syscall number is in r8**
+  *  For syscalls, the syscall number is in r8
-  *  **r9-r15 are for temporary values (may get trampled)**
+  *  r9-r15 are for temporary values - called function may clobber these values
   *  r16-r18 are used for intra-procedure-call and platform values (avoid)
-  *  **The called routine is expected to preserve r19-r28. These registers are generally safe to use in your program.**
+  *  r19-r28 must be preserved by a called procedure. These registers are generally safe to use in a program that calls other procedures (functions/methods/subroutines). If you are writing a procedure, you must either avoid using these registers, or save the values in these registers and restore them before returning.
   *  r29 and r30 are used as the frame register and link register (avoid)