build: Add initial support for aarch64 build

This commit introduces initial support for aarch64 build. It adds build
scripts and bootstrap assembly code.

Signed-off-by: Akira Moroo <[email protected]>

Author: retrage

aarch64-unknown-none.json

@@ -0,0 +1,20 @@
+{
+  "llvm-target": "aarch64-unknown-none",
+  "abi": "softfloat",
+  "arch": "aarch64",
+  "data-layout": "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128",
+  "disable-redzone": true,
+  "features": "+strict-align,-neon,-fp-armv8",
+  "linker": "rust-lld",
+  "linker-flavor": "ld.lld",
+  "os": "none",
+  "executables": true,
+  "max-atomic-width": 128,
+  "panic-strategy": "abort",
+  "code-model": "small",
+  "relocation-model": "pic",
+  "target-pointer-width": "64",
+  "pre-link-args": {
+    "ld.lld": ["--script=aarch64-unknown-none.ld", "--oformat=binary"]
+  }
+}

aarch64-unknown-none.ld

@@ -0,0 +1,39 @@
+ENTRY(ram64_start)
+
+/* Cloud Hypervisor Memory layout:
+    DRAM:   [0x4000_0000-0xfc00_0000]
+    FDT:    [0x4000_0000-0x401f_ffff)
+    ACPI:   [0x4020_0000-0x403f_ffff)
+    kernel: [0x4048_0000-]
+   The stack start is at the end of the DRAM region. */
+ram_min = 0x40480000;
+
+SECTIONS
+{
+  /* Mapping the program headers and note into RAM makes the file smaller. */
+  . = ram_min;
+
+  /* These sections are mapped into RAM from the file. Omitting :ram from
+     later sections avoids emitting empty sections in the final binary.       */
+  text_start = .;
+  .text.boot : { *(.text.boot) }
+  .text   : { *(.text .text.*)     }
+  . = ALIGN(4K);
+  text_end = .;
+  .data   : { *(.data .data.*)     }
+  .note : { *(.note) }
+  .rodata : { *(.rodata .rodata.*) }
+
+  /* The BSS section isn't mapped from file data. It is just zeroed in RAM. */
+  .bss : {
+    bss_start = .;
+    *(.bss .bss.*)
+    bss_size = . - bss_start;
+  }
+
+  /* Strip symbols from the output binary (comment out to get symbols) */
+  /DISCARD/ : {
+    *(.symtab)
+    *(.strtab)
+  }
+}

build.rs

@@ -1,4 +1,6 @@
 fn main() {
+    println!("cargo:rerun-if-changed=aarch64-unknown-none.json");
+    println!("cargo:rerun-if-changed=aarch64-unknown-none.ld");
     println!("cargo:rerun-if-changed=x86_64-unknown-none.json");
     println!("cargo:rerun-if-changed=x86_64-unknown-none.ld");
 }

rust-toolchain.toml

@@ -1,5 +1,5 @@
 [toolchain]
 channel = "nightly-2022-06-10"
 components = ["rust-src", "clippy", "rustfmt"]
-targets = ["x86_64-unknown-linux-gnu"]
+targets = ["aarch64-unknown-linux-gnu", "x86_64-unknown-linux-gnu"]
 profile = "default"

src/arch/aarch64/asm.rs

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright (C) 2022 Akira Moroo
+
+use core::arch::global_asm;
+
+global_asm!(include_str!("ram64.s"));

src/arch/aarch64/mod.rs

@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright (C) 2022 Akira Moroo
+
+#[cfg(not(test))]
+pub mod asm;

src/arch/aarch64/ram64.s

@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+/* Copyright (C) 2022 Akira Moroo */
+
+.section .text.boot, "ax"
+.global ram64_start
+
+ram64_start:
+  /* UEFI "MZ" signature magic instruction */
+  add x13, x18, #0x16   /* code0 */
+  b jump_to_rust        /* code1 */
+
+  .quad 0               /* text_offset */
+  .quad 0               /* image_size */
+  .quad 0               /* flags */
+  .quad 0               /* res2 */
+  .quad 0               /* res3 */
+  .quad 0               /* res4 */
+
+  .long 0x644d5241      /* "ARM\x64" magic number */
+  .long 0               /* res5 */
+  .align 3
+
+jump_to_rust:
+  /* x0 typically points to device tree at entry */
+  ldr x0, =0x40000000
+
+  /* setup stack */
+  ldr x30, =0xfc000000
+  mov sp, x30
+
+  /* x0: pointer to device tree */
+  b rust64_start

src/arch/mod.rs

@@ -1,5 +1,8 @@
 // SPDX-License-Identifier: Apache-2.0
 // Copyright (C) 2022 Akira Moroo
 
+#[cfg(target_arch = "aarch64")]
+pub mod aarch64;
+
 #[cfg(target_arch = "x86_64")]
 pub mod x86_64;

src/pe.rs

@@ -38,10 +38,12 @@ struct Section {
 }
 
 impl<'a> Loader<'a> {
+    #[cfg(target_arch = "aarch64")]
+    const MACHINE_TYPE: u16 = 0xaa64;
     #[cfg(target_arch = "x86_64")]
     const MACHINE_TYPE: u16 = 0x8664;
 
-    #[cfg(target_arch = "x86_64")]
+    #[cfg(any(target_arch = "aarch64", target_arch = "x86_64"))]
     const OPTIONAL_HEADER_MAGIC: u16 = 0x20b; // PE32+
 
     pub fn new(file: &'a mut dyn crate::fat::Read) -> Loader {