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Message-ID: <2dbd1491-149d-443c-9802-75786a6a3b73@gmail.com>
Date: Mon, 17 Jun 2024 18:03:11 +0200
From: Christian Schrefl <chrisi.schrefl@...il.com>
To: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 rust-for-linux@...r.kernel.org
Cc: Miguel Ojeda <ojeda@...nel.org>, Jamie Cunliffe <Jamie.Cunliffe@....com>,
 Sven Van Asbroeck <thesven73@...il.com>,
 Geert Stappers <stappers@...ppers.nl>, Andrew Lunn <andrew@...n.ch>
Subject: [PATCH v2] arm: rust: Enable Rust support for ARMv7

This commit allows building ARMv7 kernels with Rust support.

The rust core library expects some __eabi_... functions
that are not implemented in the kernel.
Those functions are some float operations and __aeabi_uldivmod.
For now those are implemented with define_panicking_intrinsics!.

This is based on the code by Sven Van Asbroeck from the original
rust branch and inspired by the AArch64 version by Jamie Cunliffe.

I have tested the rust samples and a custom simple MMIO module
on hardware (De1SoC FPGA + Arm A9 CPU).

This only includes support for ARMv7, but supporting other
sub-architectures in the future should be as simple as setting 
the correct rustc target.

Signed-off-by: Christian Schrefl <chrisi.schrefl@...il.com>
---
Changes since V1 [1]:
- Removed unrelated whitespace change.
- Added target name to panic message in scripts/generate_rust_target.rs.
- Fixed the comment in rust/bindgen_parameters.


[1]: https://lore.kernel.org/rust-for-linux/4e0f5932-c7bc-4878-862c-1186cbecd71d@gmail.com 
--
 Documentation/rust/arch-support.rst |  1 +
 arch/arm/Kconfig                    |  1 +
 arch/arm/Makefile                   |  1 +
 rust/Makefile                       |  8 ++++++++
 rust/bindgen_parameters             |  4 ++++
 rust/compiler_builtins.rs           | 24 ++++++++++++++++++++++++
 scripts/generate_rust_target.rs     |  4 +++-
 7 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index b13e19d84744..4bf5205f526d 100644
--- a/Documentation/rust/arch-support.rst
+++ b/Documentation/rust/arch-support.rst
@@ -15,6 +15,7 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
 =============  ================  ==============================================
 Architecture   Level of support  Constraints
 =============  ================  ==============================================
+``arm``        Maintained        ARMv7 Little Endian only.
 ``arm64``      Maintained        Little Endian only.
 ``loongarch``  Maintained        \-
 ``riscv``      Maintained        ``riscv64`` only.
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ee5115252aac..f07149fe078b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -126,6 +126,7 @@ config ARM
 	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
+	select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UID16
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 71afdd98ddf2..9cc10e32e8be 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -150,6 +150,7 @@ endif
 KBUILD_CPPFLAGS	+=$(cpp-y)
 KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
 KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(AFLAGS_ISA) -Wa,$(arch-y) $(tune-y) -include asm/unified.h -msoft-float
+KBUILD_RUSTFLAGS += --target=arm-unknown-linux-gnueabi
 
 CHECKFLAGS	+= -D__arm__
 
diff --git a/rust/Makefile b/rust/Makefile
index f70d5e244fee..8214a6f378e3 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -287,6 +287,7 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
 # Derived from `scripts/Makefile.clang`.
 BINDGEN_TARGET_x86	:= x86_64-linux-gnu
 BINDGEN_TARGET_arm64	:= aarch64-linux-gnu
+BINDGEN_TARGET_arm	:= arm-linux-gnueabi
 BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))
 
 # All warnings are inhibited since GCC builds are very experimental,
@@ -413,6 +414,13 @@ redirect-intrinsics = \
 	__muloti4 __multi3 \
 	__udivmodti4 __udivti3 __umodti3
 
+ifdef CONFIG_ARM
+	# Add eabi initrinsics for ARM 32-bit
+	redirect-intrinsics += \
+		__aeabi_fadd __aeabi_fmul __aeabi_fcmpeq __aeabi_fcmple __aeabi_fcmplt __aeabi_fcmpun \
+		__aeabi_dadd __aeabi_dmul __aeabi_dcmple __aeabi_dcmplt __aeabi_dcmpun \
+		__aeabi_uldivmod
+endif
 ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
 	# These intrinsics are defined for ARM64 and RISCV64
 	redirect-intrinsics += \
diff --git a/rust/bindgen_parameters b/rust/bindgen_parameters
index a721d466bee4..83f28ae4bb2b 100644
--- a/rust/bindgen_parameters
+++ b/rust/bindgen_parameters
@@ -24,3 +24,7 @@
 # These functions use the `__preserve_most` calling convention, which neither bindgen
 # nor Rust currently understand, and which Clang currently declares to be unstable.
 --blocklist-function __list_.*_report
+
+# Depending on how the architecture defines `ARCH_SLAB_MINALIGN`, `bindgen` might generate a binding.
+# Disable this here as there is a `const` item that will always be generated in `bindings_helper.h`
+--blocklist-item ARCH_SLAB_MINALIGN
diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
index bba2922c6ef7..c37142b16a45 100644
--- a/rust/compiler_builtins.rs
+++ b/rust/compiler_builtins.rs
@@ -70,5 +70,29 @@ pub extern "C" fn $ident() {
     __umodti3,
 });
 
+#[cfg(target_arch = "arm")]
+define_panicking_intrinsics!("`f32` should not be used", {
+    __aeabi_fadd,
+    __aeabi_fmul,
+    __aeabi_fcmpeq,
+    __aeabi_fcmple,
+    __aeabi_fcmplt,
+    __aeabi_fcmpun,
+});
+
+#[cfg(target_arch = "arm")]
+define_panicking_intrinsics!("`f64` should not be used", {
+    __aeabi_dadd,
+    __aeabi_dmul,
+    __aeabi_dcmple,
+    __aeabi_dcmplt,
+    __aeabi_dcmpun,
+});
+
+#[cfg(target_arch = "arm")]
+define_panicking_intrinsics!("`u64` division/modulo should not be used", {
+    __aeabi_uldivmod,
+});
+
 // NOTE: if you are adding a new intrinsic here, you should also add it to
 // `redirect-intrinsics` in `rust/Makefile`.
diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
index 641b713a033a..c3a6058fdf30 100644
--- a/scripts/generate_rust_target.rs
+++ b/scripts/generate_rust_target.rs
@@ -148,7 +148,9 @@ fn main() {
     let mut ts = TargetSpec::new();
 
     // `llvm-target`s are taken from `scripts/Makefile.clang`.
-    if cfg.has("ARM64") {
+    if cfg.has("ARM") {
+        panic!("arm uses the builtin rustc arm-unknown-linux-gnueabi target");
+    } else if cfg.has("ARM64") {
         panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
     } else if cfg.has("RISCV") {
         if cfg.has("64BIT") {

base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
-- 
2.45.2

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