From fa9002a374541675d36f861232ae868b095722b3 Mon Sep 17 00:00:00 2001
From: johannst <johannes.stoelp@gmail.com>
Date: Mon, 28 Sep 2020 20:54:03 +0200
Subject: added asm skeleton from arm64

---
 src/arch/README.md |  1 +
 src/arch/arm64.md  | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 src/arch/arm64.md

(limited to 'src/arch')

diff --git a/src/arch/README.md b/src/arch/README.md
index 48f0332..b14cd98 100644
--- a/src/arch/README.md
+++ b/src/arch/README.md
@@ -1,3 +1,4 @@
 # Arch
 
 - [x86_64](./x86_64.md)
+- [arm64](./arm64.md)
diff --git a/src/arch/arm64.md b/src/arch/arm64.md
new file mode 100644
index 0000000..2286bd8
--- /dev/null
+++ b/src/arch/arm64.md
@@ -0,0 +1,65 @@
+# arm64
+keywords: arm64, aarch64, abi
+
+- 64bit synonyms: `arm64`, `aarch64`
+- ISA type: `RISC`
+- Endianness: `little`, `big`
+
+
+## ASM skeleton
+Small assembler skeleton, ready to use with following properties:
+- use raw Linux syscalls (`man 2 syscall` for ABI)
+- no `C runtime (crt)`
+- gnu assembler [`gas`][gas_doc]
+```armasm
+// file: greet.S
+
+#include <asm/unistd.h>      // syscall NRs
+
+    .arch armv8-a
+
+    .section .text, "ax", @progbits
+    .align 2
+    .global _start
+_start:
+    mov x0, 2                // fd
+    ldr x1, =greeting        // buf
+    ldr x2, =greeting_len    // &len
+    ldr x2, [x2]             // len
+    mov w8, __NR_write       // write(2) syscall
+    svc 0
+
+    mov x0, 0                // exit code
+    mov w8, __NR_exit        // exit(2) syscall
+    svc 0
+
+    .align 3
+    .section .rodata, "a", @progbits
+greeting:
+    .asciz "Hi ASM-World!\n"
+greeting_len:
+    .int .-greeting
+```
+> man gcc: `file.S` assembler code that must be preprocessed.
+
+To cross-compile and run:
+```bash
+> aarch64-linux-gnu-g++ -o greet greet.S -nostartfiles -nostdlib          \
+    -Wl,--dynamic-linker=/usr/aarch64-linux-gnu/lib/ld-linux-aarch64.so.1 \
+  && qemu-aarch64 ./greet
+Hi ASM-World!
+```
+> Cross-compiling on `Ubuntu 20.04`, paths might differ on other distributions.
+> Compiling natively on arm64, specifying the dynamic linker should not be required.
+
+## References
+- [Procedure Call Standard ARM64][aapcs64]
+- [ARMv8 Programmer's Guide][armv8a_prog_guide]
+- [GNU Assembler][gas_doc]
+- [GNU Assembler Directives][gas_directives]
+
+
+[aapcs64]: https://github.com/ARM-software/abi-aa/blob/master/aapcs64/aapcs64.rst
+[armv8a_prog_guide]: https://developer.arm.com/documentation/den0024/a
+[gas_doc]: https://sourceware.org/binutils/docs/as
+[gas_directives]: https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops
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