semihosting 0.1.25

Semihosting for AArch64, Arm, RISC-V, LoongArch, MIPS32, MIPS64, and Xtensa.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153

// SPDX-License-Identifier: Apache-2.0 OR MIT

// The rustc-cfg emitted by the build script are *not* public API.

#[path = "src/gen/build.rs"]
mod generated;
#[path = "version.rs"]
mod version;

use std::env;

use self::version::{Version, rustc_version};

fn main() {
    println!("cargo:rerun-if-changed=build.rs");
    println!("cargo:rerun-if-changed=src/gen/build.rs");

    let target_arch = &*env::var("CARGO_CFG_TARGET_ARCH").expect("CARGO_CFG_TARGET_ARCH not set");

    let version = match rustc_version() {
        Some(version) => version,
        None => {
            if env::var_os("SEMIHOSTING_DENY_WARNINGS").is_some() {
                panic!("unable to determine rustc version")
            }
            println!(
                "cargo:warning={}: unable to determine rustc version; assuming latest stable rustc (1.{})",
                env!("CARGO_PKG_NAME"),
                Version::LATEST.minor
            );
            Version::LATEST
        }
    };

    if version.minor >= 80 {
        // Custom cfgs set by build script. Not public API.
        // grep -F 'cargo:rustc-cfg=' build.rs | grep -Ev '^ *//' | sed -E 's/^.*cargo:rustc-cfg=//; s/(=\\)?".*$//' | LC_ALL=C sort -u | tr '\n' ',' | sed -E 's/,$/\n/'
        println!(
            "cargo:rustc-check-cfg=cfg(semihosting_no_asm,semihosting_no_duration_checked_float,semihosting_no_error_in_core,semihosting_no_strict_provenance,semihosting_target_feature)"
        );
        // TODO: handle multi-line target_feature_fallback
        // grep -F 'target_feature_fallback("' build.rs | grep -Ev '^ *//' | sed -E 's/^.*target_feature_fallback\(//; s/",.*$/"/' | LC_ALL=C sort -u | tr '\n' ',' | sed -E 's/,$/\n/'
        println!(
            r#"cargo:rustc-check-cfg=cfg(semihosting_target_feature,values("mclass","thumb-mode"))"#
        );
    }

    // Note that cfgs are `no_`*, not `has_*`. This allows treating as the latest
    // stable rustc is used when the build script doesn't run. This is useful
    // for non-cargo build systems that don't run the build script.

    // duration_checked_float stabilized in Rust 1.66 (nightly-2022-10-25): https://github.com/rust-lang/rust/pull/102271
    if !version.probe(66, 2022, 10, 24) {
        println!("cargo:rustc-cfg=semihosting_no_duration_checked_float");
    }
    // error_in_core stabilized in Rust 1.81 (nightly-2024-06-09): https://github.com/rust-lang/rust/pull/125951
    if !version.probe(81, 2024, 6, 8) {
        println!("cargo:rustc-cfg=semihosting_no_error_in_core");
    }
    // strict_provenance/exposed_provenance APIs stabilized in Rust 1.84 (nightly-2024-10-22): https://github.com/rust-lang/rust/pull/130350
    if !version.probe(84, 2024, 10, 21) {
        println!("cargo:rustc-cfg=semihosting_no_strict_provenance");
    }

    match target_arch {
        "arm" => {
            let target = &*env::var("TARGET").expect("TARGET not set");

            // https://github.com/rust-lang/rust/pull/123745 (includes https://github.com/rust-lang/cargo/pull/13560) merged in Rust 1.79 (nightly-2024-04-11).
            if !version.probe(79, 2024, 4, 10) {
                // HACK: If --target is specified, rustflags is not applied to the build
                // script itself, so the build script will not be recompiled when rustflags
                // is changed. That in itself is not a problem, but the old Cargo does
                // not rerun the build script as well, which can be problematic.
                // https://github.com/rust-lang/cargo/issues/13003
                // This problem has been fixed in 1.79 so only older versions need a workaround.
                println!("cargo:rerun-if-env-changed=CARGO_ENCODED_RUSTFLAGS");
                println!("cargo:rerun-if-env-changed=RUSTFLAGS");
                println!("cargo:rerun-if-env-changed=CARGO_BUILD_RUSTFLAGS");
                let mut target_upper = target.replace(['-', '.'], "_");
                target_upper.make_ascii_uppercase();
                println!("cargo:rerun-if-env-changed=CARGO_TARGET_{target_upper}_RUSTFLAGS");
            }

            if needs_target_feature_fallback(&version) {
                // See https://github.com/taiki-e/atomic-maybe-uninit/blob/HEAD/build.rs for details
                let mut subarch =
                    target.strip_prefix("arm").or_else(|| target.strip_prefix("thumb")).unwrap();
                subarch = subarch.strip_prefix("eb").unwrap_or(subarch); // ignore endianness
                subarch = subarch.split('-').next().unwrap(); // ignore vender/os/env
                subarch = subarch.split('.').next().unwrap(); // ignore .base/.main suffix
                let mut mclass = false;
                match subarch {
                    "v6m" | "v7em" | "v7m" | "v8m" => mclass = true,
                    _ => {}
                }
                target_feature_fallback("mclass", mclass);
                // All builtin targets that start with "thumb" enable thumb-mode, and
                // some builtin targets that start with "arm" are also enable thumb-mode.
                let thumb_mode =
                    target.starts_with("thumb") || generated::ARM_BUT_THUMB_MODE.contains(&target);
                target_feature_fallback("thumb-mode", thumb_mode);
            }
        }
        "loongarch32" => {
            // asm! on loongarch32 stabilized in Rust 1.91 (nightly-2025-08-11): https://github.com/rust-lang/rust/pull/144402
            if !version.probe(91, 2025, 8, 10) {
                println!("cargo:rustc-cfg=semihosting_no_asm");
            }
        }
        _ => {}
    }
}

// HACK: Currently, it seems that the only way to handle unstable target
// features on the stable is to parse the `-C target-feature` in RUSTFLAGS.
//
// - #[cfg(target_feature = "unstable_target_feature")] doesn't work on stable.
// - CARGO_CFG_TARGET_FEATURE excludes unstable target features on stable.
//
// As mentioned in the [RFC2045], unstable target features are also passed to LLVM
// (e.g., https://godbolt.org/z/4rr7rMcfG), so this hack works properly on stable.
//
// [RFC2045]: https://rust-lang.github.io/rfcs/2045-target-feature.html#backend-compilation-options
fn needs_target_feature_fallback(version: &Version) -> bool {
    if version.nightly {
        // In this case, cfg(target_feature = "...") would work, so skip emitting our own fallback target_feature cfg.
        false
    } else {
        true
    }
}
fn target_feature_fallback(name: &str, mut has_target_feature: bool) {
    if let Some(rustflags) = env::var_os("CARGO_ENCODED_RUSTFLAGS") {
        for mut flag in rustflags.to_string_lossy().split('\x1f') {
            flag = flag.strip_prefix("-C").unwrap_or(flag);
            if let Some(flag) = flag.strip_prefix("target-feature=") {
                for s in flag.split(',') {
                    // TODO: Handles cases where a specific target feature
                    // implicitly enables another target feature.
                    match (s.as_bytes().first(), s.as_bytes().get(1..)) {
                        (Some(b'+'), Some(f)) if f == name.as_bytes() => has_target_feature = true,
                        (Some(b'-'), Some(f)) if f == name.as_bytes() => has_target_feature = false,
                        _ => {}
                    }
                }
            }
        }
    }
    if has_target_feature {
        println!("cargo:rustc-cfg=semihosting_target_feature=\"{name}\"");
    }
}