Building libcamera for Raspberry Pi

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1

Hi,

After the arm32-on-arm64 issue was resolved in Cross-compiling 'hello' to raspberryPi I’m trying to cross-compile more advanced packages. However, I keep running into a problem where the compiler-rt-libc fails to build because of invalid assembler instructions. A snippet:

compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S: Assembler messages:
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `dmb' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `ldrex r0,[r12]' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: cannot honor width suffix -- `add r2,r0,r1'
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `strex r3,r2,[r12]' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `dmb' in Thumb mode

Taken from the command

$ nix build -L github:NixOS/nixpkgs/7eeb326217be38cf0c86e38edf1ec57aa2a974be#pkgs.pkgsCross.raspberryPi.libcamera

running on a NixOS 22.11 aarch64-linux VM.

full log at gist:4f4be6ac9c0c5703637eb9855b5448da · GitHub

Elias

2

Strange, I think I’ve fixed this issue back in 348d19ad, which should be in NixOS 22.11.

3

Something is explicitly depending on clang 11, rather than the default version. This requires a real fix to compiler-rt, which I’m working on here: compiler-rt: fix build on ARMv6 by lopsided98 · Pull Request #205176 · NixOS/nixpkgs · GitHub

4

Thanks everyone!

@rnhmjoj Note that I’m building on NixOS 22.11, but referencing a very recent nixpkgs-unstable commit. Not sure if that makes any difference.

@lopsided98 thanks, that’s very helpful. To workaround the build issue, can I somehow define my own raspberryPi platform specifying armv6k?

5

I’m not sure how to do it from the command line with flakes (you need to pass the crossSystem argument when evaluating nixpkgs), but when building a NixOS system this should work:

nixpkgs.crossSystem = {
      system = "armv6l-linux";
      gcc.arch = "armv6k";
};
6

Thank you, @lopsided98. I’m hitting a hard-float error now:

cc1: error: '-mfloat-abi=hard': selected architecture lacks an FPU

full log: gist:5786516187b0194ce9f8e73c0930ed45 · GitHub

It’s my understanding that the rpi0 has a FPU. Do I need to tweak the crossSystem further?

Elias

7

Yeah, I guess you need:

gcc = {
  arch = "armv6k";
  fpu = "vfp";
};
8

This is the definition of the normal raspberryPi platform for reference: nixpkgs/platforms.nix at a5bcb6e77a0d579d4792049461b52f74e77f065d · NixOS/nixpkgs · GitHub

9

Thank you. I’m now getting the same error as initially,

compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S: Assembler messages:
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `dmb' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `ldrex r0,[r12]' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: cannot honor width suffix -- `add r2,r0,r1'
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `strex r3,r2,[r12]' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> /build/compiler-rt-11.1.0.src/lib/builtins/arm/sync_fetch_and_add_4.S:19: Error: selected processor does not support `dmb' in Thumb mode
compiler-rt-libc-armv6l-unknown-linux-gnueabihf> make[2]: *** [lib/builtins/CMakeFiles/clang_rt.builtins-armhf.dir/build.make:193: lib/builtins/CMakeFiles/clang_rt.builtins-armhf.dir/arm/sync_fetch_and_add_

my nixpkgs is this:

        crosspkgs = import nixpkgs {
          system = "${arch}-linux";
          crossSystem = {
            system = "armv6l-linux";
            gcc = {
              arch = "armv6k";
              fpu = "vfp";
            };
          };
        };

and I’m running

nix build .#crosspkgs.libcamera

What did I miss? The configuration seems to have ignored the armv6k part.

Elias

10

Perhaps I misunderstood your arch="armv6k" to mean that I didn’t need your PR 205176 for my particular case. I’m retrying the build, this time with your PR applied on a local nixpkgs clone.

11

Success! libcamera built without error with the PR applied. I still don’t understand why arch="armv6k" doesn’t alleviate the problem with assembly instructions.