Apple: Refactor deployment target version parsing

- Merge minimum OS version list into one function (makes it easier to
  see the logic in it).
- Parse patch deployment target versions.
- Consistently specify deployment target in LLVM target (previously
  omitted on `aarch64-apple-watchos`).

Author: madsmtm

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -372,27 +372,42 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
     Some(file)
 }
 
-/// Since Xcode 15 Apple's LD requires object files to contain information about what they were
-/// built for (LC_BUILD_VERSION): the platform (macOS/watchOS etc), minimum OS version, and SDK
-/// version. This returns a `MachOBuildVersion` for the target.
+/// Mach-O files contain information about:
+/// - The platform/OS they were built for (macOS/watchOS/Mac Catalyst/iOS simulator etc).
+/// - The minimum OS version / deployment target.
+/// - The version of the SDK they were targetting.
+///
+/// In the past, this was accomplished using the LC_VERSION_MIN_MACOSX, LC_VERSION_MIN_IPHONEOS,
+/// LC_VERSION_MIN_TVOS or LC_VERSION_MIN_WATCHOS load commands, which each contain information
+/// about the deployment target and SDK version, and implicitly, by their presence, which OS they
+/// target. Simulator targets were determined if the architecture was x86_64, but there was e.g. a
+/// LC_VERSION_MIN_IPHONEOS present.
+///
+/// This is of course brittle and limited, so modern tooling emit the LC_BUILD_VERSION load
+/// command (which contains all three pieces of information in one) when the deployment target is
+/// high enough, or the target is something that wouldn't be encodable with the old load commands
+/// (such as Mac Catalyst, or Aarch64 iOS simulator).
+///
+/// Since Xcode 15, Apple's LD apparently requires object files to use this load command, so this
+/// returns the `MachOBuildVersion` for the target to do so.
 fn macho_object_build_version_for_target(target: &Target) -> object::write::MachOBuildVersion {
     /// The `object` crate demands "X.Y.Z encoded in nibbles as xxxx.yy.zz"
     /// e.g. minOS 14.0 = 0x000E0000, or SDK 16.2 = 0x00100200
-    fn pack_version((major, minor): (u32, u32)) -> u32 {
-        (major << 16) | (minor << 8)
+    fn pack_version((major, minor, patch): (u16, u8, u8)) -> u32 {
+        let (major, minor, patch) = (major as u32, minor as u32, patch as u32);
+        (major << 16) | (minor << 8) | patch
     }
 
     let platform =
         rustc_target::spec::current_apple_platform(target).expect("unknown Apple target OS");
-    let min_os = rustc_target::spec::current_apple_deployment_target(target)
-        .expect("unknown Apple target OS");
-    let sdk =
+    let min_os = rustc_target::spec::current_apple_deployment_target(target);
+    let (sdk_major, sdk_minor) =
         rustc_target::spec::current_apple_sdk_version(platform).expect("unknown Apple target OS");
 
     let mut build_version = object::write::MachOBuildVersion::default();
     build_version.platform = platform;
     build_version.minos = pack_version(min_os);
-    build_version.sdk = pack_version(sdk);
+    build_version.sdk = pack_version((sdk_major, sdk_minor, 0));
     build_version
 }
 

compiler/rustc_driver_impl/src/lib.rs

@@ -871,9 +871,9 @@ fn print_crate_info(
                 use rustc_target::spec::current_apple_deployment_target;
 
                 if sess.target.is_like_osx {
-                    let (major, minor) = current_apple_deployment_target(&sess.target)
-                        .expect("unknown Apple target OS");
-                    println_info!("deployment_target={}", format!("{major}.{minor}"))
+                    let (major, minor, patch) = current_apple_deployment_target(&sess.target);
+                    let patch = if patch != 0 { format!(".{patch}") } else { String::new() };
+                    println_info!("deployment_target={major}.{minor}{patch}")
                 } else {
                     #[allow(rustc::diagnostic_outside_of_impl)]
                     sess.dcx().fatal("only Apple targets currently support deployment version info")

compiler/rustc_target/src/spec/base/apple/mod.rs

@@ -1,5 +1,6 @@
 use std::borrow::Cow;
 use std::env;
+use std::num::ParseIntError;
 
 use crate::spec::{
     add_link_args, add_link_args_iter, cvs, Cc, DebuginfoKind, FramePointer, LinkArgs,
@@ -123,15 +124,8 @@ fn pre_link_args(os: &'static str, arch: Arch, abi: TargetAbi) -> LinkArgs {
     };
 
     let min_version: StaticCow<str> = {
-        let (major, minor) = match os {
-            "ios" => ios_deployment_target(arch, abi.target_abi()),
-            "tvos" => tvos_deployment_target(),
-            "watchos" => watchos_deployment_target(),
-            "visionos" => visionos_deployment_target(),
-            "macos" => macos_deployment_target(arch),
-            _ => unreachable!(),
-        };
-        format!("{major}.{minor}").into()
+        let (major, minor, patch) = deployment_target(os, arch, abi);
+        format!("{major}.{minor}.{patch}").into()
     };
     let sdk_version = min_version.clone();
 
@@ -161,15 +155,22 @@ fn pre_link_args(os: &'static str, arch: Arch, abi: TargetAbi) -> LinkArgs {
         add_link_args_iter(
             &mut args,
             LinkerFlavor::Darwin(Cc::Yes, Lld::No),
-            ["-target".into(), mac_catalyst_llvm_target(arch).into()].into_iter(),
+            ["-target".into(), llvm_target(os, arch, abi)].into_iter(),
         );
     }
 
     args
 }
 
-pub(crate) fn opts(os: &'static str, arch: Arch, abi: TargetAbi) -> TargetOptions {
-    TargetOptions {
+/// Get the base target options, LLVM target and `target_arch` from the three
+/// things that uniquely identify Rust's Apple targets: The OS, the
+/// architecture, and the ABI.
+pub(crate) fn base(
+    os: &'static str,
+    arch: Arch,
+    abi: TargetAbi,
+) -> (TargetOptions, StaticCow<str>, StaticCow<str>) {
+    let opts = TargetOptions {
         abi: abi.target_abi().into(),
         os: os.into(),
         cpu: arch.target_cpu(abi).into(),
@@ -219,10 +220,11 @@ pub(crate) fn opts(os: &'static str, arch: Arch, abi: TargetAbi) -> TargetOption
         link_env: Cow::Borrowed(&[(Cow::Borrowed("ZERO_AR_DATE"), Cow::Borrowed("1"))]),
 
         ..Default::default()
-    }
+    };
+    (opts, llvm_target(os, arch, abi), arch.target_arch())
 }
 
-pub fn sdk_version(platform: u32) -> Option<(u32, u32)> {
+pub fn sdk_version(platform: u32) -> Option<(u16, u8)> {
     // NOTE: These values are from an arbitrary point in time but shouldn't make it into the final
     // binary since the final link command will have the current SDK version passed to it.
     match platform {
@@ -256,58 +258,108 @@ pub fn platform(target: &Target) -> Option<u32> {
     })
 }
 
-pub fn deployment_target(target: &Target) -> Option<(u32, u32)> {
-    let (major, minor) = match &*target.os {
-        "macos" => {
-            // This does not need to be specific. It just needs to handle x86 vs M1.
-            let arch = match target.arch.as_ref() {
-                "x86" | "x86_64" => X86_64,
-                "arm64e" => Arm64e,
-                _ => Arm64,
-            };
-            macos_deployment_target(arch)
-        }
-        "ios" => {
-            let arch = match target.arch.as_ref() {
-                "arm64e" => Arm64e,
-                _ => Arm64,
-            };
-            ios_deployment_target(arch, &target.abi)
-        }
-        "watchos" => watchos_deployment_target(),
-        "tvos" => tvos_deployment_target(),
-        "visionos" => visionos_deployment_target(),
-        _ => return None,
+/// Hack for calling `deployment_target` outside of this module.
+pub fn deployment_target_for_target(target: &Target) -> (u16, u8, u8) {
+    let arch = if target.llvm_target.starts_with("arm64e") {
+        Arch::Arm64e
+    } else if target.arch == "aarch64" {
+        Arch::Arm64
+    } else {
+        // Dummy architecture, only used by `deployment_target` anyhow
+        Arch::X86_64
     };
-
-    Some((major, minor))
+    let abi = match &*target.abi {
+        "macabi" => TargetAbi::MacCatalyst,
+        "sim" => TargetAbi::Simulator,
+        "" => TargetAbi::Normal,
+        abi => unreachable!("invalid abi '{abi}' for Apple target"),
+    };
+    deployment_target(&target.os, arch, abi)
 }
 
-fn from_set_deployment_target(var_name: &str) -> Option<(u32, u32)> {
-    let deployment_target = env::var(var_name).ok()?;
-    let (unparsed_major, unparsed_minor) = deployment_target.split_once('.')?;
-    let (major, minor) = (unparsed_major.parse().ok()?, unparsed_minor.parse().ok()?);
+/// Get the deployment target based on the standard environment variables, or
+/// fall back to a sane default.
+fn deployment_target(os: &str, arch: Arch, abi: TargetAbi) -> (u16, u8, u8) {
+    // When bumping a version in here, remember to update the platform-support
+    // docs too.
+    //
+    // NOTE: If you are looking for the default deployment target, prefer
+    // `rustc --print deployment-target`, as the default here may change in
+    // future `rustc` versions.
+
+    // Minimum operating system versions currently supported by `rustc`.
+    let os_min = match os {
+        "macos" => (10, 12, 0),
+        "ios" => (10, 0, 0),
+        "tvos" => (10, 0, 0),
+        "watchos" => (5, 0, 0),
+        "visionos" => (1, 0, 0),
+        _ => unreachable!("tried to get deployment target for non-Apple platform"),
+    };
 
-    Some((major, minor))
-}
+    // On certain targets it makes sense to raise the minimum OS version.
+    let min = match (os, arch, abi) {
+        // Use 11.0 on Aarch64 as that's the earliest version with M1 support.
+        ("macos", Arch::Arm64 | Arch::Arm64e, _) => (11, 0, 0),
+        ("ios", Arch::Arm64e, _) => (14, 0, 0),
+        // Mac Catalyst defaults to 13.1 in Clang.
+        ("ios", _, TargetAbi::MacCatalyst) => (13, 1, 0),
+        _ => os_min,
+    };
 
-fn macos_default_deployment_target(arch: Arch) -> (u32, u32) {
-    match arch {
-        Arm64 | Arm64e => (11, 0),
-        _ => (10, 12),
-    }
-}
+    // The environment variable used to fetch the deployment target.
+    let env_var = match os {
+        "macos" => "MACOSX_DEPLOYMENT_TARGET",
+        "ios" => "IPHONEOS_DEPLOYMENT_TARGET",
+        "watchos" => "WATCHOS_DEPLOYMENT_TARGET",
+        "tvos" => "TVOS_DEPLOYMENT_TARGET",
+        "visionos" => "XROS_DEPLOYMENT_TARGET",
+        _ => unreachable!("tried to get deployment target env var for non-Apple platform"),
+    };
 
-fn macos_deployment_target(arch: Arch) -> (u32, u32) {
-    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
-    // Note: If bumping this version, remember to update it in the rustc/platform-support docs.
-    from_set_deployment_target("MACOSX_DEPLOYMENT_TARGET")
-        .unwrap_or_else(|| macos_default_deployment_target(arch))
+    if let Ok(deployment_target) = env::var(env_var) {
+        match parse_version(&deployment_target) {
+            // It is common that the deployment target is set too low, e.g. on
+            // macOS Aarch64 to also target older x86_64, the user may set a
+            // lower deployment target than supported.
+            //
+            // To avoid such issues, we silently raise the deployment target
+            // here.
+            // FIXME: We want to show a warning when `version < os_min`.
+            Ok(version) => version.max(min),
+            // FIXME: Report erroneous environment variable to user.
+            Err(_) => min,
+        }
+    } else {
+        min
+    }
 }
 
-pub(crate) fn macos_llvm_target(arch: Arch) -> String {
-    let (major, minor) = macos_deployment_target(arch);
-    format!("{}-apple-macosx{}.{}.0", arch.target_name(), major, minor)
+/// Generate the target triple that we need to pass to LLVM and/or Clang.
+fn llvm_target(os: &str, arch: Arch, abi: TargetAbi) -> StaticCow<str> {
+    // The target triple depends on the deployment target, and is required to
+    // enable features such as cross-language LTO, and for picking the right
+    // Mach-O commands.
+    //
+    // Certain optimizations also depend on the deployment target.
+    let (major, minor, patch) = deployment_target(os, arch, abi);
+    let arch = arch.target_name();
+    // Convert to the "canonical" OS name used by LLVM:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L236-L282
+    let os = match os {
+        "macos" => "macosx",
+        "ios" => "ios",
+        "watchos" => "watchos",
+        "tvos" => "tvos",
+        "visionos" => "xros",
+        _ => unreachable!("tried to get LLVM target OS for non-Apple platform"),
+    };
+    let environment = match abi {
+        TargetAbi::Normal => "",
+        TargetAbi::MacCatalyst => "-macabi",
+        TargetAbi::Simulator => "-simulator",
+    };
+    format!("{arch}-apple-{os}{major}.{minor}.{patch}{environment}").into()
 }
 
 fn link_env_remove(os: &'static str) -> StaticCow<[StaticCow<str>]> {
@@ -347,83 +399,19 @@ fn link_env_remove(os: &'static str) -> StaticCow<[StaticCow<str>]> {
     }
 }
 
-fn ios_deployment_target(arch: Arch, abi: &str) -> (u32, u32) {
-    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
-    // Note: If bumping this version, remember to update it in the rustc/platform-support docs.
-    let (major, minor) = match (arch, abi) {
-        (Arm64e, _) => (14, 0),
-        // Mac Catalyst defaults to 13.1 in Clang.
-        (_, "macabi") => (13, 1),
-        _ => (10, 0),
-    };
-    from_set_deployment_target("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or((major, minor))
-}
-
-pub(crate) fn ios_llvm_target(arch: Arch) -> String {
-    // Modern iOS tooling extracts information about deployment target
-    // from LC_BUILD_VERSION. This load command will only be emitted when
-    // we build with a version specific `llvm_target`, with the version
-    // set high enough. Luckily one LC_BUILD_VERSION is enough, for Xcode
-    // to pick it up (since std and core are still built with the fallback
-    // of version 7.0 and hence emit the old LC_IPHONE_MIN_VERSION).
-    let (major, minor) = ios_deployment_target(arch, "");
-    format!("{}-apple-ios{}.{}.0", arch.target_name(), major, minor)
-}
-
-pub(crate) fn mac_catalyst_llvm_target(arch: Arch) -> String {
-    let (major, minor) = ios_deployment_target(arch, "macabi");
-    format!("{}-apple-ios{}.{}.0-macabi", arch.target_name(), major, minor)
-}
-
-pub(crate) fn ios_sim_llvm_target(arch: Arch) -> String {
-    let (major, minor) = ios_deployment_target(arch, "sim");
-    format!("{}-apple-ios{}.{}.0-simulator", arch.target_name(), major, minor)
-}
-
-fn tvos_deployment_target() -> (u32, u32) {
-    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
-    // Note: If bumping this version, remember to update it in the rustc platform-support docs.
-    from_set_deployment_target("TVOS_DEPLOYMENT_TARGET").unwrap_or((10, 0))
-}
-
-pub(crate) fn tvos_llvm_target(arch: Arch) -> String {
-    let (major, minor) = tvos_deployment_target();
-    format!("{}-apple-tvos{}.{}.0", arch.target_name(), major, minor)
-}
-
-pub(crate) fn tvos_sim_llvm_target(arch: Arch) -> String {
-    let (major, minor) = tvos_deployment_target();
-    format!("{}-apple-tvos{}.{}.0-simulator", arch.target_name(), major, minor)
-}
-
-fn watchos_deployment_target() -> (u32, u32) {
-    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
-    // Note: If bumping this version, remember to update it in the rustc platform-support docs.
-    from_set_deployment_target("WATCHOS_DEPLOYMENT_TARGET").unwrap_or((5, 0))
-}
-
-pub(crate) fn watchos_llvm_target(arch: Arch) -> String {
-    let (major, minor) = watchos_deployment_target();
-    format!("{}-apple-watchos{}.{}.0", arch.target_name(), major, minor)
-}
-
-pub(crate) fn watchos_sim_llvm_target(arch: Arch) -> String {
-    let (major, minor) = watchos_deployment_target();
-    format!("{}-apple-watchos{}.{}.0-simulator", arch.target_name(), major, minor)
-}
-
-fn visionos_deployment_target() -> (u32, u32) {
-    // If you are looking for the default deployment target, prefer `rustc --print deployment-target`.
-    // Note: If bumping this version, remember to update it in the rustc platform-support docs.
-    from_set_deployment_target("XROS_DEPLOYMENT_TARGET").unwrap_or((1, 0))
-}
-
-pub(crate) fn visionos_llvm_target(arch: Arch) -> String {
-    let (major, minor) = visionos_deployment_target();
-    format!("{}-apple-visionos{}.{}.0", arch.target_name(), major, minor)
-}
-
-pub(crate) fn visionos_sim_llvm_target(arch: Arch) -> String {
-    let (major, minor) = visionos_deployment_target();
-    format!("{}-apple-visionos{}.{}.0-simulator", arch.target_name(), major, minor)
+/// Parse an OS version triple (SDK version or deployment target).
+///
+/// The size of the returned numbers here are limited by Mach-O's
+/// `LC_BUILD_VERSION`.
+fn parse_version(version: &str) -> Result<(u16, u8, u8), ParseIntError> {
+    if let Some((major, minor)) = version.split_once('.') {
+        let major = major.parse()?;
+        if let Some((minor, patch)) = minor.split_once('.') {
+            Ok((major, minor.parse()?, patch.parse()?))
+        } else {
+            Ok((major, minor.parse()?, 0))
+        }
+    } else {
+        Ok((version.parse()?, 0, 0))
+    }
 }

compiler/rustc_target/src/spec/base/apple/tests.rs

@@ -1,3 +1,4 @@
+use super::parse_version;
 use crate::spec::targets::{
     aarch64_apple_darwin, aarch64_apple_ios_sim, aarch64_apple_visionos_sim,
     aarch64_apple_watchos_sim, i686_apple_darwin, x86_64_apple_darwin, x86_64_apple_ios,
@@ -42,3 +43,11 @@ fn macos_link_environment_unmodified() {
         );
     }
 }
+
+#[test]
+fn test_parse_version() {
+    assert_eq!(parse_version("10"), Ok((10, 0, 0)));
+    assert_eq!(parse_version("10.12"), Ok((10, 12, 0)));
+    assert_eq!(parse_version("10.12.6"), Ok((10, 12, 6)));
+    assert_eq!(parse_version("9999.99.99"), Ok((9999, 99, 99)));
+}