Add a rust+zig example for hexagon

Signed-off-by: Brian Cain <[email protected]>

examples/contrived/.cargo/config.toml

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+
+[build]
+target = [ "hexagon-unknown-linux-musl"]
+
+[target.hexagon-unknown-linux-musl]
+
+linker = "hexagon-unknown-linux-musl-clang"
+runner = "qemu-hexagon"
+

examples/contrived/.gitignore

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+/target
+*.swp
+*.a
+*.a.o

examples/contrived/Cargo.toml

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+[package]
+name = "contrived"
+version = "0.1.0"
+edition = "2021"
+build = "build.rs"
+
+[build-dependencies]
+cc = "1.1.21"
+bindgen = "0.70.1"
+build-target = "0.4.0"
+
+[dependencies]
+

examples/contrived/README.md

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+# Contrived example
+
+This is a contrived example to demonstrate some toolchains targeting
+hexagon linux.  Here we illustrate how to use Rust, Zig, and C++ to
+write programs portable to hexagon similarly to how one would
+target other architectures.
+
+We can use the upstream Rust toolchain with lld to make programs for hexagon
+linux.  There might be yet-undiscovered bugs, but there's no known limitations
+for this platform.
+
+As of September 2024, Zig does not yet have support for hexagon linux, only
+`hexagon-freestanding` (baremetal hexagon).  This is primarily because the
+C library support is not yet upstreamed to `musl`.  As a consequence we
+cannot yet `@import("std")`.  Also, with any zig code, compiler-emitted
+calls to the compiler builtin libraries could result in some "unresolved
+symbol" link errors.  These could probably be solved with some creative
+workarounds/linker command-line overrides.  See the [issue at the
+zig project for details](https://github.com/ziglang/zig/issues/21579).
+
+## Dependencies
+
+[Download zig](https://ziglang.org/download/), unpack the tarball and put
+the `zig` executable in your `PATH`.
+
+[Install rust using the instructions from the Rust Project website](https://www.rust-lang.org/learn/get-started)
+and then install the nightly:
+
+    rustup toolchain install nightly
+    rustup override set nightly
+    rustup component add rust-src --toolchain nightly-x86_64-unknown-linux-gnu
+
+Download and install the hexagon open source toolchain from https://github.com/quic/toolchain_for_hexagon/releases - version 19.1.0 or later.
+
+## Setup
+
+Edit the `.cargo/config` to point to your toolchain's C library:
+
+    ...
+    runner = "qemu-hexagon -L /inst/clang+llvm-19.1.0-cross-hexagon-unknown-linux-musl/x86_64-linux-gnu/target/hexagon-unknown-linux-musl/usr"
+    ...
+
+
+## Build and run
+
+Build/run the demo with QEMU hexagon:
+
+    export TARGET_CC=hexagon-unknown-linux-musl-clang
+    export PATH=/inst/clang+llvm-19.1.0-cross-hexagon-unknown-linux-musl/x86_64-linux-gnu/bin/:$PATH
+    export QEMU_LD_PREFIX=/inst/clang+llvm-19.1.0-cross-hexagon-unknown-linux-musl/x86_64-linux-musl/target/hexagon-unknown-linux-musl/usr/
+
+    cargo +nightly build --target=hexagon-unknown-linux-musl -Zbuild-std  -Zbuild-std-features=llvm-libunwind
+    cargo +nightly run --target=hexagon-unknown-linux-musl -Zbuild-std  -Zbuild-std-features=llvm-libunwind
+
+Try experimenting with some different input arguments to see how this impacts
+the cycles consumed.
+
+As a simpler reference, you can also run this natively on an `x86_64` host
+(you might need to manually clean up some `*.a` / `*.a.o` files):
+
+    CXX=clang++ CC=clang cargo run --target=x86_64-unknown-linux-gnu
+

examples/contrived/build.rs

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+// Copyright(c) 2024 Qualcomm Innovation Center, Inc. All Rights Reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+use std::process::Command;
+
+fn main() {
+    println!("cargo::rerun-if-changed=src/hex_sys.cpp");
+
+    cc::Build::new()
+        .file("src/some_cxx.cpp")
+        .compile("libsome_cxx.a");
+    println!("cargo:rustc-link-lib=some_cxx");
+
+    let arch = build_target::target_arch().unwrap();
+    let arch = arch.as_str();
+
+    let zig_tgt = match arch {
+        "hexagon" => "hexagon-freestanding",
+        "x86_64" => "x86_64-linux-gnu",
+        _ => panic!("unsupported target"),
+    };
+
+    println!("cargo::rerun-if-changed=src/some_sys.zig");
+    let rc = Command::new("zig")
+        .arg("build-lib")
+        .arg("-fPIC")
+        .arg("-target")
+        .arg(zig_tgt)
+        .arg("src/some_sys.zig")
+        .status()
+        .expect("failed to spawn process");
+    assert!(rc.success());
+
+    println!("cargo:rustc-link-search=.");
+    println!("cargo:rustc-link-lib=some_sys");
+}

examples/contrived/src/main.rs

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+// Copyright(c) 2024 Qualcomm Innovation Center, Inc. All Rights Reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+use std::env;
+
+extern "C" {
+    fn read_activity() -> u64;
+    fn get_cycles() -> u64;
+    fn get_time() -> u64;
+}
+
+fn fibonacci(n: u32) -> u32 {
+    match n {
+        0 => 1,
+        1 => 1,
+        _ => fibonacci(n - 1) + fibonacci(n - 2),
+    }
+}
+
+fn main() {
+    let arg: String = env::args().nth(1).unwrap_or("16".to_string());
+    let in_val = arg.parse::<u32>().unwrap_or(16);
+
+    let t0 = unsafe { read_activity() };
+    let v = fibonacci(in_val);
+    let dur_cycl = unsafe { read_activity() } - t0;
+
+    println!("fibonacci({}): {}", in_val, v);
+    println!("cycles elapsed: {}", dur_cycl);
+
+    let t0 = unsafe { get_cycles() };
+    let v_ = fibonacci(in_val);
+    let t_end = unsafe { get_cycles() } - t0;
+
+    println!("fibonacci({}): {}", in_val, v_);
+    println!("cycles elapsed: {}", t_end);
+
+    println!("cur time: {}", unsafe { get_time() });
+}

examples/contrived/src/some_cxx.cpp

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+// Copyright(c) 2024 Qualcomm Innovation Center, Inc. All Rights Reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include <stdint.h>
+
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wc23-extensions"
+
+static const int32_t raw_data[] = {
+#embed "lut.dat"
+};
+#pragma clang diagnostic pop
+
+
+#define ARRAY_ELTS(x) (sizeof(x) / sizeof(x[0]))
+
+int32_t get_val(unsigned int index) {
+    return raw_data[index % ARRAY_ELTS(raw_data)];
+}
+
+extern "C" uint64_t get_cycles() {
+    return __builtin_readcyclecounter();
+}
+
+#if !defined(__clang_major__) || __clang_major__ < 19
+#error "requires clang 19.1.x or later"
+#endif
+
+extern "C" uint64_t get_time() {
+    return __builtin_readsteadycounter();
+}

examples/contrived/src/some_sys.zig

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+// Copyright(c) 2024 Qualcomm Innovation Center, Inc. All Rights Reserved.
+// SPDX-License-Identifier: BSD-3-Clause
+
+const builtin = @import("builtin");
+
+// Ehh...it's not really the same thing between these
+// architectures, but ¯\_(ツ)_/¯ we are just illustrating
+// concepts here...
+
+export fn read_activity() u64 {
+    if (comptime builtin.cpu.arch == .hexagon) {
+        return asm volatile ("%[value] = upcycle"
+            : [value] "=&r" (-> u64),
+        );
+    } else if (comptime builtin.cpu.arch == .x86_64) {
+        var high: u64 = 0;
+        var low: u64 = 0;
+
+        asm volatile (
+            \\rdtsc
+            : [low] "={eax}" (low),
+              [high] "={edx}" (high),
+        );
+        return (@as(u64, high) << 32) | @as(u64, low);
+    } else {
+        const std = @import("std");
+        const msg = std.fmt.comptimePrint("unsupported architecture: '{s}'", .{@tagName(builtin.cpu.arch)});
+
+        @compileError(msg);
+    }
+}