From ab0f4cedc3554f921691ce5b63d59e258154e799 Mon Sep 17 00:00:00 2001
From: David Gow <davidgow@google.com>
Date: Wed, 5 Jun 2024 06:40:50 +0800
Subject: [PATCH] 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: 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>
---
Documentation/rust/arch-support.rst | 2 +-
arch/um/Kconfig | 2 +-
rust/Makefile | 2 +-
scripts/Makefile | 2 +-
scripts/generate_rust_target.rs | 17 +++++++++++++++++
5 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index b13e19d847443..750ff371570a0 100644
--- a/Documentation/rust/arch-support.rst
+++ b/Documentation/rust/arch-support.rst
@@ -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.
============= ================ ==============================================
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 7580167311568..e08a4a1a4bb6c 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -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
diff --git a/rust/Makefile b/rust/Makefile
index f70d5e244fee5..83f675adbfabd 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -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)),)
$(obj)/core.o: scripts/target.json
endif
diff --git a/scripts/Makefile b/scripts/Makefile
index fe56eeef09dd4..dccef663ca820 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -12,7 +12,7 @@ hostprogs-always-$(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
diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
index 641b713a033a7..87f34925eb7b7 100644
--- a/scripts/generate_rust_target.rs
+++ b/scripts/generate_rust_target.rs
@@ -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 {
--
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