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Move Apple linker args from rustc_target to rustc_codegen_ssa
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They are dependent on the deployment target and SDK version, but having
these in `rustc_target` makes it hard to introduce that dependency.
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@madsmtm
madsmtm committed Sep 26, 2024
1 parent f2becdf commit fb10eeb
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Showing 2 changed files with 134 additions and 121 deletions.
133 changes: 132 additions & 1 deletion compiler/rustc_codegen_ssa/src/back/link.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ use rustc_target::spec::crt_objects::CrtObjects;
use rustc_target::spec::{
Cc, LinkOutputKind, LinkSelfContainedComponents, LinkSelfContainedDefault, LinkerFeatures,
LinkerFlavor, LinkerFlavorCli, Lld, PanicStrategy, RelocModel, RelroLevel, SanitizerSet,
SplitDebuginfo,
SplitDebuginfo, current_apple_deployment_target,
};
use tempfile::Builder as TempFileBuilder;
use tracing::{debug, info, warn};
Expand Down Expand Up @@ -2405,6 +2405,8 @@ fn add_order_independent_options(
// Take care of the flavors and CLI options requesting the `lld` linker.
add_lld_args(cmd, sess, flavor, self_contained_components);

add_apple_link_args(cmd, sess, flavor);

let apple_sdk_root = add_apple_sdk(cmd, sess, flavor);

add_link_script(cmd, sess, tmpdir, crate_type);
Expand Down Expand Up @@ -2957,6 +2959,135 @@ pub(crate) fn are_upstream_rust_objects_already_included(sess: &Session) -> bool
}
}

/// We need to communicate four things to the linker on Apple/Darwin targets:
/// - The architecture.
/// - The operating system (and that it's an Apple platform).
/// - The deployment target.
/// - The environment / ABI.
fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
if !sess.target.is_like_osx {
return;
}
let LinkerFlavor::Darwin(cc, _) = flavor else {
return;
};

// `sess.target.arch` (`target_arch`) is not detailed enough.
let llvm_arch = sess.target.llvm_target.split_once('-').expect("LLVM target must have arch").0;
let target_os = &*sess.target.os;
let target_abi = &*sess.target.abi;

// The architecture name to forward to the linker.
//
// Supported architecture names can be found in the source:
// https://github.com/apple-oss-distributions/ld64/blob/ld64-951.9/src/abstraction/MachOFileAbstraction.hpp#L578-L648
//
// Intentially verbose to ensure that the list always matches correctly
// with the list in the source above.
let ld64_arch = match llvm_arch {
"armv7k" => "armv7k",
"armv7s" => "armv7s",
"arm64" => "arm64",
"arm64e" => "arm64e",
"arm64_32" => "arm64_32",
// ld64 doesn't understand i686, so fall back to i386 instead.
//
// Same story when linking with cc, since that ends up invoking ld64.
"i386" | "i686" => "i386",
"x86_64" => "x86_64",
"x86_64h" => "x86_64h",
_ => bug!("unsupported architecture in Apple target: {}", sess.target.llvm_target),
};

if cc == Cc::No {
// From the man page for ld64 (`man ld`):
// > The linker accepts universal (multiple-architecture) input files,
// > but always creates a "thin" (single-architecture), standard
// > Mach-O output file. The architecture for the output file is
// > specified using the -arch option.
//
// The linker has heuristics to determine the desired architecture,
// but to be safe, and to avoid a warning, we set the architecture
// explicitly.
cmd.link_args(&["-arch", ld64_arch]);

// Man page says that ld64 supports the following platform names:
// > - macos
// > - ios
// > - tvos
// > - watchos
// > - bridgeos
// > - visionos
// > - xros
// > - mac-catalyst
// > - ios-simulator
// > - tvos-simulator
// > - watchos-simulator
// > - visionos-simulator
// > - xros-simulator
// > - driverkit
let platform_name = match (target_os, target_abi) {
(os, "") => os,
("ios", "macabi") => "mac-catalyst",
("ios", "sim") => "ios-simulator",
("tvos", "sim") => "tvos-simulator",
("watchos", "sim") => "watchos-simulator",
("visionos", "sim") => "visionos-simulator",
_ => bug!("invalid OS/ABI combination for Apple target: {target_os}, {target_abi}"),
};

let (major, minor, patch) = current_apple_deployment_target(&sess.target);
let min_version = format!("{major}.{minor}.{patch}");

// Lie about the SDK version, we don't know it here
let sdk_version = &*min_version;

// From the man page for ld64 (`man ld`):
// > This is set to indicate the platform, oldest supported version of
// > that platform that output is to be used on, and the SDK that the
// > output was built against.
//
// Like with `-arch`, the linker can figure out the platform versions
// itself from the binaries being linked, but to be safe, we specify
// the desired versions here explicitly.
cmd.link_args(&["-platform_version", platform_name, &*min_version, sdk_version]);
} else {
// cc == Cc::Yes
// We'd _like_ to use `-target` everywhere, since that can uniquely
// communicate all the required details, but that doesn't work on GCC,
// and since we don't know whether the `cc` compiler is Clang, GCC, or
// something else, we fall back to other options that also work on GCC
// when compiling for macOS.
//
// Targets other than macOS are ill-supported by GCC (it doesn't even
// support e.g. `-miphoneos-version-min`), so in those cases we can
// fairly safely use `-target`. See also the following, where it is
// made explicit that the recommendation by LLVM developers is to use
// `-target`: <https://github.com/llvm/llvm-project/issues/88271>
if target_os == "macos" {
// `-arch` communicates the architecture.
//
// CC forwards the `-arch` to the linker, so we use the same value
// here intentionally.
cmd.cc_args(&["-arch", ld64_arch]);

// The presence of `-mmacosx-version-min` makes CC default to
// macOS, and it sets the deployment target.
let (major, minor, patch) = current_apple_deployment_target(&sess.target);
// Intentionally pass this as a single argument, Clang doesn't
// seem to like it otherwise.
cmd.cc_arg(&format!("-mmacosx-version-min={major}.{minor}.{patch}"));

// macOS has no environment, so with these two, we've told CC the
// four desired parameters.
//
// We avoid `-m32`/`-m64`, as this is already encoded by `-arch`.
} else {
cmd.cc_args(&["-target", &sess.target.llvm_target]);
}
}
}

fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) -> Option<PathBuf> {
let arch = &sess.target.arch;
let os = &sess.target.os;
Expand Down
122 changes: 2 additions & 120 deletions compiler/rustc_target/src/spec/base/apple/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,8 @@ use std::env;
use std::num::ParseIntError;

use crate::spec::{
Cc, DebuginfoKind, FramePointer, LinkArgs, LinkerFlavor, Lld, SplitDebuginfo, StackProbeType,
StaticCow, Target, TargetOptions, add_link_args, add_link_args_iter, cvs,
Cc, DebuginfoKind, FramePointer, LinkerFlavor, Lld, SplitDebuginfo, StackProbeType, StaticCow,
Target, TargetOptions, cvs,
};

#[cfg(test)]
Expand Down Expand Up @@ -40,25 +40,6 @@ impl Arch {
}
}

/// The architecture name to forward to the linker.
fn ld_arch(self) -> &'static str {
// Supported architecture names can be found in the source:
// https://github.com/apple-oss-distributions/ld64/blob/ld64-951.9/src/abstraction/MachOFileAbstraction.hpp#L578-L648
match self {
Armv7k => "armv7k",
Armv7s => "armv7s",
Arm64 => "arm64",
Arm64e => "arm64e",
Arm64_32 => "arm64_32",
// ld64 doesn't understand i686, so fall back to i386 instead
//
// Same story when linking with cc, since that ends up invoking ld64.
I386 | I686 => "i386",
X86_64 => "x86_64",
X86_64h => "x86_64h",
}
}

pub(crate) fn target_arch(self) -> Cow<'static, str> {
Cow::Borrowed(match self {
Armv7k | Armv7s => "arm",
Expand Down Expand Up @@ -116,104 +97,6 @@ impl TargetAbi {
}
}

fn pre_link_args(os: &'static str, arch: Arch, abi: TargetAbi) -> LinkArgs {
// From the man page for ld64 (`man ld`):
// > The linker accepts universal (multiple-architecture) input files,
// > but always creates a "thin" (single-architecture), standard Mach-O
// > output file. The architecture for the output file is specified using
// > the -arch option.
//
// The linker has heuristics to determine the desired architecture, but to
// be safe, and to avoid a warning, we set the architecture explicitly.
let mut args =
TargetOptions::link_args(LinkerFlavor::Darwin(Cc::No, Lld::No), &["-arch", arch.ld_arch()]);

// From the man page for ld64 (`man ld`):
// > This is set to indicate the platform, oldest supported version of
// > that platform that output is to be used on, and the SDK that the
// > output was built against. platform [...] may be one of the following
// > strings:
// > - macos
// > - ios
// > - tvos
// > - watchos
// > - bridgeos
// > - visionos
// > - xros
// > - mac-catalyst
// > - ios-simulator
// > - tvos-simulator
// > - watchos-simulator
// > - visionos-simulator
// > - xros-simulator
// > - driverkit
//
// Like with `-arch`, the linker can figure out the platform versions
// itself from the binaries being linked, but to be safe, we specify the
// desired versions here explicitly.
let platform_name: StaticCow<str> = match abi {
TargetAbi::Normal => os.into(),
TargetAbi::Simulator => format!("{os}-simulator").into(),
TargetAbi::MacCatalyst => "mac-catalyst".into(),
};
let min_version: StaticCow<str> = {
let (major, minor, patch) = deployment_target(os, arch, abi);
format!("{major}.{minor}.{patch}").into()
};
// Lie about the SDK version, we don't know it here
let sdk_version = min_version.clone();
add_link_args_iter(
&mut args,
LinkerFlavor::Darwin(Cc::No, Lld::No),
["-platform_version".into(), platform_name, min_version, sdk_version].into_iter(),
);

// We need to communicate four things to the C compiler to be able to link:
// - The architecture.
// - The operating system (and that it's an Apple platform).
// - The deployment target.
// - The environment / ABI.
//
// We'd like to use `-target` everywhere, since that can uniquely
// communicate all of these, but that doesn't work on GCC, and since we
// don't know whether the `cc` compiler is Clang, GCC, or something else,
// we fall back to other options that also work on GCC when compiling for
// macOS.
//
// Targets other than macOS are ill-supported by GCC (it doesn't even
// support e.g. `-miphoneos-version-min`), so in those cases we can fairly
// safely use `-target`. See also the following, where it is made explicit
// that the recommendation by LLVM developers is to use `-target`:
// <https://github.com/llvm/llvm-project/issues/88271>
if os == "macos" {
// `-arch` communicates the architecture.
//
// CC forwards the `-arch` to the linker, so we use the same value
// here intentionally.
add_link_args(&mut args, LinkerFlavor::Darwin(Cc::Yes, Lld::No), &[
"-arch",
arch.ld_arch(),
]);
// The presence of `-mmacosx-version-min` makes CC default to macOS,
// and it sets the deployment target.
let (major, minor, patch) = deployment_target(os, arch, abi);
let opt = format!("-mmacosx-version-min={major}.{minor}.{patch}").into();
add_link_args_iter(&mut args, LinkerFlavor::Darwin(Cc::Yes, Lld::No), [opt].into_iter());
// macOS has no environment, so with these two, we've told CC all the
// desired parameters.
//
// We avoid `-m32`/`-m64`, as this is already encoded by `-arch`.
} else {
add_link_args_iter(
&mut args,
LinkerFlavor::Darwin(Cc::Yes, Lld::No),
["-target".into(), llvm_target(os, arch, abi)].into_iter(),
);
}

args
}

/// 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.
Expand All @@ -232,7 +115,6 @@ pub(crate) fn base(
// macOS has -dead_strip, which doesn't rely on function_sections
function_sections: false,
dynamic_linking: true,
pre_link_args: pre_link_args(os, arch, abi),
families: cvs!["unix"],
is_like_osx: true,
// LLVM notes that macOS 10.11+ and iOS 9+ default
Expand Down

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