`hexagon-unknown-none-elf`

Tier: 3

Rust for baremetal Hexagon DSPs.

Target	Descriptions
hexagon-unknown-none-elf	Hexagon 32-bit (freestanding, hardfloat)

Requirements

This target is cross-compiled. There is no support for std. There is no default allocator, but it's possible to use alloc by supplying an allocator.

By default, code generated with this target should run on Hexagon DSP hardware.

-Ctarget-cpu=hexagonv73 adds support for instructions defined up to Hexagon V73.

Functions marked extern "C" use the Hexagon architecture calling convention.

This target generates PIC ELF binaries.

Building the target

You can build Rust with support for the target by adding it to the target list in config.toml:

[build]
build-stage = 1
host = ["<target for your host>"]
target = ["<target for your host>", "hexagon-unknown-none-elf"]

[target.hexagon-unknown-none-elf]

cc = "hexagon-unknown-none-elf-clang"
cxx = "hexagon-unknown-none-elf-clang++"
linker = "hexagon-unknown-none-elf-clang"
ranlib = "hexagon-unknown-none-elf-ranlib"
ar = "hexagon-unknown-none-elf-ar"
llvm-libunwind = 'in-tree'

Replace <target for your host> with x86_64-unknown-linux-gnu or whatever else is appropriate for your host machine.

Rust does not yet ship pre-compiled artifacts for this target. To compile for this target, you will either need to build Rust with the target enabled (see "Building the target" above), or build your own copy of core by using build-std or similar.

Testing

Since hexagon-unknown-none-elf supports a variety of different environments and does not support std, this target does not support running the Rust test suite.

Cross-compilation toolchains and C code

This target has been tested using qemu-system-hexagon.

A common use case for hexagon-unknown-none-elf is building libraries that link against C code and can be used in emulation or on a device with a Hexagon DSP.

The Hexagon SDK has libraries which are useful to link against when running on a device.

Standalone OS

The script below will build an executable against "hexagon standalone OS" which is suitable for emulation or bare-metal on-device testing.

First, run cargo new --bin demo1_hexagon then add the source below as src/main.rs. This program demonstrates the console output via semihosting.

#![no_std]
#![no_main]

extern "C" {
    fn putchar(ch: i32);
    fn _exit(code: i32) -> !;
}

#[no_mangle]
extern "C" fn main() -> i32 {
    let message = "Hello, this is Rust!";
    for b in message.bytes() {
        unsafe {
            putchar(b as i32);
        }
    }
    0
}

#[panic_handler]
fn panic(_panic: &core::panic::PanicInfo) -> ! {
    unsafe {
        _exit(1);
    }
}

Next, save the script below as build.sh and edit it to suit your environment.

hex_toolchain below refers to the hexagon toolchain using exclusively public open source repos.
cc below refers to clang. You can use clang from your distribution, as long as it's at least clang-17. Or you can use hexagon-unknown-none-elf-clang from one of the hexagon open source toolchain releases.

# Hexagon SDK, required for target libraries:
hex_sdk_root=/local/mnt/workspace/Qualcomm/Hexagon_SDK/5.3.0.0
hex_sdk_toolchain=${hex_sdk_root}/tools/HEXAGON_Tools/8.6.06

sdk_libs=${hex_sdk_toolchain}/Tools/target/hexagon/lib
q6_arch=v65
g0_lib_path=${sdk_libs}/${q6_arch}/G0
pic_lib_path=${sdk_libs}/${q6_arch}/G0/pic

build_cfg=release
cargo build --target=hexagon-unknown-none-elf -Zbuild-std --release

# Builds an executable against "hexagon standalone OS" suitable for emulation:
${cc} --target=hexagon-unknown-none-elf -o testit \
    -fuse-ld=lld \
    -m${q6_arch} \
    -nodefaultlibs \
    -nostartfiles \
    ${g0_lib_path}/crt0_standalone.o \
    ${g0_lib_path}/crt0.o \
    ${g0_lib_path}/init.o \
    -L${sdk_libs}/${q6_arch}/ \
    -L${sdk_libs}/ \
    wrap.c \
    target/hexagon-unknown-none-elf/${build_cfg}/libdemo1_hexagon.rlib \
    target/hexagon-unknown-none-elf/${build_cfg}/deps/libcore-*.rlib \
    target/hexagon-unknown-none-elf/${build_cfg}/deps/libcompiler_builtins-*.rlib \
    -Wl,--start-group \
    -Wl,--defsym,_SDA_BASE_=0,--defsym,__sbss_start=0,--defsym,__sbss_end=0 \
    ${g0_lib_path}/libstandalone.a \
    ${g0_lib_path}/libc.a \
    -lgcc \
    -lc_eh \
    -Wl,--end-group \
    ${g0_lib_path}/fini.o \

${hex_toolchain}/x86_64-linux-gnu/bin/qemu-system-hexagon -monitor none -display none -kernel ./testit

QuRT OS

First, run cargo new --lib demo2_hexagon then add the source below as src/lib.rs. This program demonstrates inline assembly and console output via semihosting.

#![no_std]
#![no_main]
#![feature(lang_items)]
#![feature(asm_experimental_arch)]

use core::arch::asm;

extern "C" {
    fn putchar(ch: i32);
    fn _exit(code: i32) -> !;
}

fn hexagon_specific() {
    let mut buffer = [0_u8; 128];

    unsafe {
        let mut x = &buffer;
        asm!(
                "{{\n\t",
                "  v0=vmem({addr}+#0)\n\t",
                "  {tmp} = and({tmp}, #1)\n\t",
                "}}\n\t",
                addr = in(reg) x,
                tmp = out(reg) _,
            );
    }
}

#[no_mangle]
extern "C" fn hello() -> i32 {
    let message = "Hello, this is Rust!\n";
    for b in message.bytes() {
        unsafe {
            putchar(b as i32);
        }
    }
    hexagon_specific();
    0
}

#[panic_handler]
fn panic(_panic: &core::panic::PanicInfo) -> ! {
    unsafe {
        _exit(1);
    }
}

#[lang = "eh_personality"]
fn rust_eh_personality() {}

Next, create a C program as an entry point, save the content below as wrap.c:

int hello();

int main() {
    hello();
}

Then, save the script below as build.sh and edit it to suit your environment. The script below will build a shared object against the QuRT RTOS which is suitable for emulation or on-device testing when loaded via the fastrpc-shell.

# Hexagon SDK, required for target libraries:
hex_sdk_root=/local/mnt/workspace/Qualcomm/Hexagon_SDK/5.3.0.0
hex_sdk_toolchain=${hex_sdk_root}/tools/HEXAGON_Tools/8.6.06

sdk_libs=${hex_sdk_toolchain}/Tools/target/hexagon/lib
q6_arch=v65
g0_lib_path=${sdk_libs}/${q6_arch}/G0
pic_lib_path=${sdk_libs}/${q6_arch}/G0/pic
runelf=${hex_sdk_root}/rtos/qurt/computev65/sdksim_bin/runelf.pbn
rmohs=${hex_sdk_root}/libs/run_main_on_hexagon/ship/hexagon_toolv86_${q6_arch}/run_main_on_hexagon_sim

# Builds a library suitable for loading into "run_main_on_hexagon_sim" for
# emulation or frpc shell on real target:
${cc} --target=hexagon-unknown-none-elf -o testit.so \
    -fuse-ld=lld \
    -fPIC -shared \
    -nostdlib \
    -Wl,-Bsymbolic \
      -Wl,--wrap=malloc \
      -Wl,--wrap=calloc \
      -Wl,--wrap=free \
      -Wl,--wrap=realloc \
      -Wl,--wrap=memalign \
    -m${q6_arch} \
    wrap.c \
    target/hexagon-unknown-none-elf/${build_cfg}/libdemo2_hexagon.rlib \
    target/hexagon-unknown-none-elf/${build_cfg}/deps/libcore-*.rlib \
    target/hexagon-unknown-none-elf/${build_cfg}/deps/libcompiler_builtins-*.rlib \
    -Wl,-soname=testit \
    ${pic_lib_path}/libc.so

# -Bsymbolic above for memory alloc funcs is necessary to access the heap on
# target, but otherwise not required.

# multi-stage loader: runelf => run_main_on_hexagon_sim => testit.so{`main`}
${hex_toolchain}/x86_64-linux-gnu/bin/qemu-system-hexagon \
    -monitor none \
    -display none \
    -kernel ${runelf} \
    -append "${rmohs} -- ./testit.so"

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