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Add -Zfunction-return={keep,thunk-extern} option

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This is intended to be used for Linux kernel RETHUNK builds.

With this commit (optionally backported to Rust 1.73.0), plus a
patched Linux kernel to pass the flag, I get a RETHUNK build with
Rust enabled that is `objtool`-warning-free and is able to boot in
QEMU and load a sample Rust kernel module.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Miguel Ojeda
2023-10-18 16:58:17 +02:00
parent d3c9964c20
commit 2d476222e8
17 changed files with 215 additions and 9 deletions
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24
compiler/rustc_session/src/session.rs
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@@ -1,7 +1,7 @@
use crate::code_stats::CodeStats;
pub use crate::code_stats::{DataTypeKind, FieldInfo, FieldKind, SizeKind, VariantInfo};
use crate::config::{
self, CrateType, InstrumentCoverage, OptLevel, OutFileName, OutputType,
self, CrateType, FunctionReturn, InstrumentCoverage, OptLevel, OutFileName, OutputType,
RemapPathScopeComponents, SwitchWithOptPath,
};
use crate::config::{ErrorOutputType, Input};
@@ -1678,6 +1678,28 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
sess.emit_err(errors::IncompatibleLinkerFlavor { flavor, compatible_list });
}
}
if sess.opts.unstable_opts.function_return != FunctionReturn::default() {
if sess.target.arch != "x86" && sess.target.arch != "x86_64" {
sess.emit_err(errors::FunctionReturnRequiresX86OrX8664);
}
}
// The code model check applies to `thunk` and `thunk-extern`, but not `thunk-inline`, so it is
// kept as a `match` to force a change if new ones are added, even if we currently only support
// `thunk-extern` like Clang.
match sess.opts.unstable_opts.function_return {
FunctionReturn::Keep => (),
FunctionReturn::ThunkExtern => {
// FIXME: In principle, the inherited base LLVM target code model could be large,
// but this only checks whether we were passed one explicitly (like Clang does).
if let Some(code_model) = sess.code_model()
&& code_model == CodeModel::Large
{
sess.emit_err(errors::FunctionReturnThunkExternRequiresNonLargeCodeModel);
}
}
}
}
/// Holds data on the current incremental compilation session, if there is one.