[PATCH v9 25/27] x86: enable initial Rust support

[Miguel Ojeda <ojeda@kernel.org>]

Note that only x86_64 is covered and not all features nor mitigations
are handled, but it is enough as a starting point and showcases
the basics needed to add Rust support for a new architecture.

Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Co-developed-by: David Gow <davidgow@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 Documentation/rust/arch-support.rst |  1 +
 arch/x86/Kconfig                    |  1 +
 arch/x86/Makefile                   | 10 ++++++++++
 scripts/generate_rust_target.rs     | 15 +++++++++++++--
 4 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index 1152e0fbdad0..6982b63775da 100644
--- a/Documentation/rust/arch-support.rst
+++ b/Documentation/rust/arch-support.rst
@@ -15,4 +15,5 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
 ============  ================  ==============================================
 Architecture  Level of support  Constraints
 ============  ================  ==============================================
+``x86``       Maintained        ``x86_64`` only.
 ============  ================  ==============================================
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 52a7f91527fe..4d5a3f256cbc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -258,6 +258,7 @@ config X86
 	select HAVE_STATIC_CALL_INLINE		if HAVE_OBJTOOL
 	select HAVE_PREEMPT_DYNAMIC_CALL
 	select HAVE_RSEQ
+	select HAVE_RUST			if X86_64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UACCESS_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_UNSTABLE_SCHED_CLOCK
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 7854685c5f25..bab595003f07 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -68,6 +68,7 @@ export BITS
 #    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
 #
 KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
+KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
 
 ifeq ($(CONFIG_X86_KERNEL_IBT),y)
 #
@@ -155,8 +156,17 @@ else
         cflags-$(CONFIG_GENERIC_CPU)	+= -mtune=generic
         KBUILD_CFLAGS += $(cflags-y)
 
+        rustflags-$(CONFIG_MK8)		+= -Ctarget-cpu=k8
+        rustflags-$(CONFIG_MPSC)	+= -Ctarget-cpu=nocona
+        rustflags-$(CONFIG_MCORE2)	+= -Ctarget-cpu=core2
+        rustflags-$(CONFIG_MATOM)	+= -Ctarget-cpu=atom
+        rustflags-$(CONFIG_GENERIC_CPU)	+= -Ztune-cpu=generic
+        KBUILD_RUSTFLAGS += $(rustflags-y)
+
         KBUILD_CFLAGS += -mno-red-zone
         KBUILD_CFLAGS += -mcmodel=kernel
+        KBUILD_RUSTFLAGS += -Cno-redzone=y
+        KBUILD_RUSTFLAGS += -Ccode-model=kernel
 endif
 
 #
diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
index 7256c9606cf0..3c6cbe2b278d 100644
--- a/scripts/generate_rust_target.rs
+++ b/scripts/generate_rust_target.rs
@@ -148,8 +148,19 @@ fn main() {
     let mut ts = TargetSpec::new();
 
     // `llvm-target`s are taken from `scripts/Makefile.clang`.
-    if cfg.has("DUMMY_ARCH") {
-        ts.push("arch", "dummy_arch");
+    if cfg.has("X86_64") {
+        ts.push("arch", "x86_64");
+        ts.push(
+            "data-layout",
+            "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128",
+        );
+        let mut features = "-3dnow,-3dnowa,-mmx,+soft-float".to_string();
+        if cfg.has("RETPOLINE") {
+            features += ",+retpoline-external-thunk";
+        }
+        ts.push("features", features);
+        ts.push("llvm-target", "x86_64-linux-gnu");
+        ts.push("target-pointer-width", "64");
     } else {
         panic!("Unsupported architecture");
     }
-- 
2.37.1