semihosting

Semihosting for AArch64, ARM, RISC-V (RV32 & RV64), MIPS, and MIPS64.

This library provides access to semihosting, a mechanism for programs running on the real or virtual (e.g., QEMU) target to communicate with I/O facilities on the host system. See the ARM documentation for more information on semihosting.

APIs are categorized into the following four types:

• The top-level API (semihosting::{io,fs,..}) provides a subset of the standard library's similar APIs.

  • io: Provide no-std io traits and std{in,out,err}. (std{in,out,err} requires stdio feature)
  • fs: Provide methods to manipulate the contents of the host filesystem. (requires fs feature)
  • process: Provide abort and exit.
  • dbg!/print{,ln}!/eprint{,ln}!: macros to output to stdout/stderr. (requires stdio feature)

  Note that some APIs are not strictly a subset of the standard library.

  • API that uses types not available in core such as Path (technically, the same thing could be implemented, but it makes sense to use CStr directly, because when converting a long Path/OsStr to CStr, it needs to either do an allocation or return an error)
  • API that panics on failure in std (in no-std it makes sense to return Result since panic=abort is default)

• Helpers that are useful when using this library.

  • c!: CStr literal macro.

• semihosting::sys module, which provides low-level access to platform-specific semihosting interfaces.

• semihosting::experimental module, which provides experimental APIs.

  • experimental::env::args (requires args feature)
  • experimental::time::SystemTime (requires time feature)
  • experimental::panic::catch_unwind (requires panic-unwind feature and nightly compiler)

Additionally, this library provides a panic handler for semihosting and -C panic=unwind support, via optional features.

Platform Support

The following target architectures are supported:

| target_arch | Specification | semihosting::sys module | | ----------- | ------------- | ------------------------- | | arm/aarch64 | Semihosting for AArch32 and AArch64 | sys::arm_compat | | riscv32/riscv64 | RISC-V Semihosting | sys::arm_compat | | mips/mips64 | Unified Hosting Interface (MD01069) | sys::mips |

The host must be running an emulator or a debugger attached to the target.

The following targets have been tested on CI. (qemu-system has been tested on Linux, macOS, and Windows hosts, and qemu-user on Linux host.)

| target | exit | all-apis [1] (qemu-system) | all-apis [1] (qemu-user) | panic-unwind (qemu-system [2]) | | ------------------------------------ | ---- | --------------------------- | ------------------------- | ------------------------------- | | aarch64-unknown-none{,-softfloat} | ✓ | ✓ | ✓ | ✓ | | {arm,thumb}v4t-none-eabi | ✓ | | ✓ | | | {arm,thumb}v5te-none-eabi | ✓ | | ✓ | | | armv7a-none-eabi{,hf} | ✓ | ✓ | ✓ | | | armv7r-none-eabi{,hf} | ✓ | ✓ | ✓ | | | armebv7r-none-eabi{,hf} | ✓ | | ✓ | | | thumbv6m-none-eabi | ✓ | ✓ | N/A | | | thumbv7m-none-eabi | ✓ | ✓ | N/A | | | thumbv7em-none-eabi{,hf} | ✓ | ✓ | N/A | | | thumbv8m.base-none-eabi | ✓ | * [3] | N/A | | | thumbv8m.main-none-eabi{,hf} | ✓ | * [3] | N/A | | | riscv32*-unknown-none-elf | ✓ | ✓ | ✓ | ✓ [4] | | riscv64*-unknown-none-elf | ✓ | ✓ | ✓ | ✓ | | mips{,el}-unknown-none [5] | ✓ | ✓ | N/A | | | mips64{,el}-unknown-none [5] | ✓ | ✓ | N/A | |

[1] stdio, fs, time, and args.
[2] I'm not sure how to test panic-unwind on qemu-user.
[3] It works if the host OS is Linux, but not if the host OS is any other OS. It is not clear whether the actual problem is in the host OS or the QEMU version.
[4] RISC-V RV32 support for panic-unwind requires a patch that has not yet been upstream.)
[5] Requires nightly due to #![feature(asm_experimental_arch)].

Optional features

All features are disabled by default.

In general use cases, you probably only need the stdio feature that enables print-related macros and/or the panic-handler feature that exits with a non-zero error code on panic.

toml [dependencies] semihosting = { version = "0.1", features = ["stdio", "panic-handler"] }

• alloc
  Use alloc.

• stdio
  Enable semihosting::io::{stdin,stdout,stderr} and semihosting::{print*,eprint*,dbg}.

• fs
  Enable semihosting::fs.

• args
  Enable semihosting::experimental::env::args.

  Note:

  • This feature is experimental and outside of the normal semver guarantees and minor or patch versions of semihosting may make breaking changes to them at any time.

• time
  Enable semihosting::experimental::time.

  Note:

  • This feature is experimental and outside of the normal semver guarantees and minor or patch versions of semihosting may make breaking changes to them at any time.

• panic-handler
  Provide panic handler based on semihosting::process::exit.

  If the stdio feature is also enabled, this attempt to output panic message and location to stderr.

• panic-unwind
  Provide -C panic=unwind support for panic handler and enable semihosting::experimental::panic::catch_unwind.

  This currently uses [unwinding] crate to support unwinding. See its documentation for supported platforms and requirements.

  Note:

  • This feature is experimental and outside of the normal semver guarantees and minor or patch versions of semihosting may make breaking changes to them at any time.
  • This requires nightly compiler.
  • This implicitly enables the alloc and panic-handler features.
  • This uses atomic CAS. You need to use portable-atomic feature together if your target doesn't support atomic CAS (e.g., RISC-V without A-extension).
  • When enabling this feature, you may need to rebuild the standard library with -C panic=unwind for catch_unwind to work properly. The recommended way to rebuild the standard library is passing -Z build-std="core,alloc" option to cargo.

• backtrace
  Provide backtrace support for panic handler.

  This currently uses [unwinding] crate to support backtrace. See its documentation for supported platforms and requirements.

  Note:

  • This feature is experimental and outside of the normal semver guarantees and minor or patch versions of semihosting may make breaking changes to them at any time.
  • This requires nightly compiler.
  • This implicitly enables the stdio feature.
  • When enabling this, it is recommended to also enable the panic-unwind feature. Otherwise, a decent backtrace will not be displayed at this time. (Using -C force-unwind-tables may work, but has not been tested yet.)
  • Currently, the backtrace generated is not human-readable.

  text panicked at 'a', src/main.rs:86:13 stack backtrace: 0x84dc0 0x8ed80 0x8332c 0x83654 0x80644 0x803cc 0x809dc 0x800bc

  You can use addr2line to resolve the addresses and [rustfilt] to demangle Rust symbols. For example, run the following command (please replace <path/to/binary> with your binary path), then paste the addresses:

  sh llvm-addr2line -fipe <path/to/binary> | rustfilt

• portable-atomic
  Use [portable-atomic]'s atomic types.

  portable-atomic provides atomic CAS on targets where the standard library does not provide atomic CAS. To use the panic-unwind feature on such targets (e.g., RISC-V without A-extension), you need to enable this feature.

  See the documentation for details.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.