qemu-system-aarch64: semihosting does not respect runtime-configurable endianness

Host environment

• Operating system: macOS 15.7.3
• OS/kernel version: Darwin Kernel Version 24.6.0
• Architecture: AArch64
• QEMU flavor: qemu-system-aarch64
• QEMU version: 10.2.50 (v10.2.0-283-g0fc482b73d)
• QEMU command line:

  ./build/qemu-system-aarch64-unsigned \
      -M raspi3b -display none -semihosting \
      -kernel ../semihosting/target/aarch64_be-unknown-none-softfloat/debug/no-std-test

Emulated/Virtualized environment

• Operating system: Bare-metal, the semihosting Rust crate for the aarch64_be-unknown-none-softfloat target.
• OS/kernel version: 0.1.21
• Architecture: AArch64

Description of problem

semihosting::process::exit(0) running on a QEMU-emulated AArch64 CPU in big-endian mode on a little-endian host results in the QEMU process exiting with 1 instead of 0. Potentially more tests are broken.

This is due to QEMU not respecting AArch64's runtime-configurable endianness. On semihosting::process::exit(0), in QEMU's semihosting/arm-compat-semi.c#L768, arg0 is 0x2600020000000000 and compared with ADP_Stopped_ApplicationExit, which is 0x20026. Swapping the byte order in these cases resolves the issue.

Steps to reproduce

1. Build QEMU with --target-list=aarch64-softmmu.
2. Clone github.com/taiki-e/semihosting.
3. Apply the following patch:

   --- a/tools/no-std.sh
   +++ b/tools/no-std.sh
   @@ -188,15 +188,6 @@ run() {
    
      local test_dir=tests/no-std
      case "${target}" in
   -    aarch64_be*)
   -      case "${runner}" in
   -        qemu-system)
   -          # TODO: QEMU exit with 1
   -          info "QEMU bug on aarch64_be (${target}) with system-mode (skipped)"
   -          return 0
   -          ;;
   -      esac
   -      ;;
        aarch64* | arm64* | riscv*)
          case "${runner}" in
            qemu-system)
   --- a/tools/qemu-system-runner.sh
   +++ b/tools/qemu-system-runner.sh
   @@ -56,7 +56,7 @@ qemu_system() {
      qemu_arch="$1"
      shift
    
   -  "qemu-system-${qemu_arch}" "$@" "${args[@]}"
   +  "/path-to-qemu/build/qemu-system-aarch64-unsigned" "$@" "${args[@]}"
    }
    
    export QEMU_AUDIO_DRV=none

4. ./tools/no-std.sh +nightly aarch64-unknown-none-softfloat aarch64_be-unknown-none-softfloat

Additional information

I'll post a patch to resolve this issue shortly but wanted to file an issue regardless, in case my patches are not the way to go.