使用 MacOS clang 汇编程序交叉汇编 Linux Arm64

Question

I am trying to write Assembly on MacOS using the default clang assembler.

I got this small "Hello World" working for MacOS on the same machine:

.global _main
.align 2

_main: mov X0, #1
    adr     X1, hello
    mov     X2, #13
    mov     X16, #4
    svc     0

    mov     X0, #0
    mov     X16, #1
    svc     0

hello: .ascii  "Hello World!\n"

It is taken from this question .

When I assembler it with:

clang hello.s

I can successfully run it with:

./a.out

---

Now, I try to follow the "Hello World" for Linux from the book Programming with 64-Bit ARM Assembly Language . It is basically the same program, but the sys-calls is for Linux:

.global _start

_start: mov X0, #1
    ldr     X1, =hello
    mov     X2, #13
    mov     X8, #64
    svc     0

    mov     X0, #0
    mov     X8, #93
    svc     0

.data
hello: .ascii  "Hello World!\n"

I cannot event assemble this program using clang hello.s on MacOS, I get this error:

Undefined symbols for architecture arm64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I assume that this error is because I have not told clang that it should use Linux as target.

How can I cross assemble the above "Hello World" to Linux Arm64 from MacOS on Arm64 using the built in clang?

I want to be able to run the Linux binary in a Arm64 Docker container on MacOS Arm64.

Answer 1

You will need lld or some other linker that can output ELF binaries, as Xcode only ships with Apple's ld64 , which is limited to Darwin targets. Once you have lld in your path, you can build your assembly file with:

clang --target=arm64-linux-gnu -fuse-ld=lld hello.s -nostdlib

Of course, if you want to use libraries or eventually compile C code and include header files, you will have to either find or build an SDK to pass to clang with --sysroot . I'm not aware of any standard process for doing this, but I've had some success with just pulling public deb files from Ubuntu/Debian package mirrors and unpacking them into one folder.

Answer 2

After the answer to Siguza, the difficult part was to find a linker that could do the job.

This is what finally worked for me.

Install macos cross toolchain with:

brew install aarch64-unknown-linux-gnu

After that I have this binary that can be added to PATH:

/opt/homebrew/Cellar/aarch64-unknown-linux-gnu/11.2.0/bin/aarch64-unknown-linux-gnu-ld

Then I could build the binary with:

clang --target=arm64-linux-gnu -fuse-ld=aarch64-unknown-linux-gnu-ld hello.s -nostdlib

And I could verify the binary by using this Dockerfile:

FROM scratch
ADD a.out /bin/
ENTRYPOINT ["/bin/a.out"]

Build a container with:

docker build -t app .

Run it and get the output:

docker run app
Hello World!