Commit ab0f4ced authored by David Gow's avatar David Gow Committed by Johannes Berg
Browse files

arch: um: rust: Add i386 support for Rust 

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: default avatarDavid Gow <davidgow@google.com>
Link: https://patch.msgid.link/20240604224052.3138504-1-davidgow@google.com


Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
parent 9a2123b3

Documentation/rust/arch-support.rst

+1 −1
Original line number Diff line number Diff line
@@ -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.

=============  ================  ==============================================

arch/um/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -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

rust/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

scripts/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

scripts/generate_rust_target.rs

+17 −0
Original line number Diff line number Diff line
@@ -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 {