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arch: um: rust: Add i386 support for Rust

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At present, Rust in the kernel only supports 64-bit x86, so UML has
followed suit. However, it's significantly easier to support 32-bit i386
on UML than on bare metal, as UML does not use the -mregparm option
(which alters the ABI), which is not yet supported by rustc[1].

Add support for CONFIG_RUST on um/i386, by adding a new target config to
generate_rust_target, and replacing various checks on CONFIG_X86_64 to
also support CONFIG_X86_32.

We still use generate_rust_target, rather than a built-in rustc target,
in order to match x86_64, provide a future place for -mregparm, and more
easily disable floating point instructions.

With these changes, the KUnit tests pass with:
kunit.py run --make_options LLVM=1 --kconfig_add CONFIG_RUST=y
--kconfig_add CONFIG_64BIT=n --kconfig_add CONFIG_FORTIFY_SOURCE=n

An earlier version of these changes was proposed on the Rust-for-Linux
github[2].

[1]: https://github.com/rust-lang/rust/issues/116972
[2]: https://github.com/Rust-for-Linux/linux/pull/966

Signed-off-by: David Gow <davidgow@google.com>
Link: https://patch.msgid.link/20240604224052.3138504-1-davidgow@google.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
David Gow 2024-06-05 06:40:50 +08:00 committed by Johannes Berg
parent 9a2123b397
commit ab0f4cedc3
5 changed files with 21 additions and 4 deletions
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2
Documentation/rust/arch-support.rst
View File

@ -18,7 +18,7 @@ Architecture Level of support Constraints
``arm64`` Maintained Little Endian only.
``loongarch`` Maintained \-
``riscv`` Maintained ``riscv64`` only.
``um`` Maintained ``x86_64`` only.
``um`` Maintained \-
``x86`` Maintained ``x86_64`` only.
============= ================ ==============================================

2
arch/um/Kconfig
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@ -31,7 +31,7 @@ config UML
select TRACE_IRQFLAGS_SUPPORT
select TTY # Needed for line.c
select HAVE_ARCH_VMAP_STACK
select HAVE_RUST if X86_64
select HAVE_RUST
config MMU
bool

2
rust/Makefile
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@ -426,7 +426,7 @@ $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--re
$(obj)/core.o: private rustc_target_flags = $(core-cfgs)
$(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
+$(call if_changed_dep,rustc_library)
ifdef CONFIG_X86_64
ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
$(obj)/core.o: scripts/target.json
endif

2
scripts/Makefile
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@ -12,7 +12,7 @@ hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE) += insert-sys-cert
hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS) += rustdoc_test_builder
hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS) += rustdoc_test_gen
ifdef CONFIG_X86_64
ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
always-$(CONFIG_RUST) += target.json
filechk_rust_target = $< < include/config/auto.conf

17
scripts/generate_rust_target.rs
View File

@ -169,6 +169,23 @@ fn main() {
ts.push("features", features);
ts.push("llvm-target", "x86_64-linux-gnu");
ts.push("target-pointer-width", "64");
} else if cfg.has("X86_32") {
// This only works on UML, as i386 otherwise needs regparm support in rustc
if !cfg.has("UML") {
panic!("32-bit x86 only works under UML");
}
ts.push("arch", "x86");
ts.push(
"data-layout",
"e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128",
);
let mut features = "-3dnow,-3dnowa,-mmx,+soft-float".to_string();
if cfg.has("MITIGATION_RETPOLINE") {
features += ",+retpoline-external-thunk";
}
ts.push("features", features);
ts.push("llvm-target", "i386-unknown-linux-gnu");
ts.push("target-pointer-width", "32");
} else if cfg.has("LOONGARCH") {
panic!("loongarch uses the builtin rustc loongarch64-unknown-none-softfloat target");
} else {