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Message-Id: <20250914-gcc-rust-v3-v3-1-34d4d5864144@gmail.com>
Date: Sun, 14 Sep 2025 15:16:40 +0800
From: Asuna Yang <spriteovo@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
Danilo Krummrich <dakr@...nel.org>, Jonathan Corbet <corbet@....net>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
Alexandre Ghiti <alex@...ti.fr>, Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
Han Gao <rabenda.cn@...il.com>, Jason Montleon <jmontleo@...hat.com>,
Conor Dooley <conor@...nel.org>
Cc: rust-for-linux@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
Asuna Yang <SpriteOvO@...il.com>
Subject: [PATCH v3] RISC-V: re-enable gcc + rust builds
Commit 33549fcf37ec ("RISC-V: disallow gcc + rust builds") disabled GCC
+ Rust builds for RISC-V due to differences in extension handling
compared to LLVM.
Add a Kconfig symbol to indicate the version of libclang used by Rust
bindgen and add conditions for the availability of libclang to the
RISC-V extension Kconfig symbols that depend on the cc-option function.
For Zicsr/Zifencei special handling, since LLVM/Clang always enables
these two extensions, either don't pass them to -march, or pass them
explicitly and Rust bindgen libclang must recognize them.
Clang does not support -mno-riscv-attribute flag, filter it out to
resolve error: unknown argument: '-mno-riscv-attribute'.
Define BINDGEN_TARGET_riscv to pass the target triplet to Rust bindgen
libclang for RISC-V to resolve error: unsupported argument 'medany' to
option '-mcmodel=' for target 'unknown'. Improve to output a clearer
error message if the target triplet is undefined for Rust bindgen
libclang.
Update the documentation, GCC + Rust builds are now supported.
Signed-off-by: Asuna Yang <SpriteOvO@...il.com>
---
Documentation/rust/arch-support.rst | 2 +-
arch/riscv/Kconfig | 30 +++++++++++++++++++++++++++++-
init/Kconfig | 6 ++++++
rust/Makefile | 7 ++++++-
scripts/Kconfig.include | 1 +
5 files changed, 43 insertions(+), 3 deletions(-)
diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index 6e6a515d08991a130a8e79dc4ad7ad09da244020..5282e0e174e8de66b4c6fec354cf329fd2aec873 100644
--- a/Documentation/rust/arch-support.rst
+++ b/Documentation/rust/arch-support.rst
@@ -18,7 +18,7 @@ Architecture Level of support Constraints
``arm`` Maintained ARMv7 Little Endian only.
``arm64`` Maintained Little Endian only.
``loongarch`` Maintained \-
-``riscv`` Maintained ``riscv64`` and LLVM/Clang only.
+``riscv`` Maintained ``riscv64`` only.
``um`` Maintained \-
``x86`` Maintained ``x86_64`` only.
============= ================ ==============================================
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 51dcd8eaa24356d947ebe0f1c4a701a3cfc6b757..3e892864f930778218073e8ee5980eb8f4e1594a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -191,7 +191,7 @@ config RISCV
select HAVE_REGS_AND_STACK_ACCESS_API
select HAVE_RETHOOK if !XIP_KERNEL
select HAVE_RSEQ
- select HAVE_RUST if RUSTC_SUPPORTS_RISCV && CC_IS_CLANG
+ select HAVE_RUST if RUSTC_SUPPORTS_RISCV && TOOLCHAIN_MATCHES_ZICSR_ZIFENCEI
select HAVE_SAMPLE_FTRACE_DIRECT
select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
select HAVE_STACKPROTECTOR
@@ -629,6 +629,8 @@ config TOOLCHAIN_HAS_V
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32imv)
depends on LLD_VERSION >= 140000 || LD_VERSION >= 23800
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/e6de53b4de4aecca4ac892500a0907805896ed27
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
config RISCV_ISA_V
bool "Vector extension support"
@@ -693,6 +695,8 @@ config TOOLCHAIN_HAS_ZABHA
depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zabha)
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zabha)
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/6b7444964a8d028989beee554a1f5c61d16a1cac
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 190100
config RISCV_ISA_ZABHA
bool "Zabha extension support for atomic byte/halfword operations"
@@ -711,6 +715,8 @@ config TOOLCHAIN_HAS_ZACAS
depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zacas)
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zacas)
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/614aeda93b2225c6eb42b00ba189ba7ca2585c60
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 200100
config RISCV_ISA_ZACAS
bool "Zacas extension support for atomic CAS"
@@ -730,6 +736,8 @@ config TOOLCHAIN_HAS_ZBB
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbb)
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/33d008b169f3c813a4a45da220d0952f795ac477
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
# This symbol indicates that the toolchain supports all v1.0 vector crypto
# extensions, including Zvk*, Zvbb, and Zvbc. LLVM added all of these at once.
@@ -745,6 +753,8 @@ config TOOLCHAIN_HAS_ZBA
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zba)
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/33d008b169f3c813a4a45da220d0952f795ac477
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
config RISCV_ISA_ZBA
bool "Zba extension support for bit manipulation instructions"
@@ -780,6 +790,8 @@ config TOOLCHAIN_HAS_ZBC
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbc)
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/33d008b169f3c813a4a45da220d0952f795ac477
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
config RISCV_ISA_ZBC
bool "Zbc extension support for carry-less multiplication instructions"
@@ -803,6 +815,8 @@ config TOOLCHAIN_HAS_ZBKB
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbkb)
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+ # https://github.com/llvm/llvm-project/commit/7ee1c162cc53d37f717f9a138276ad64fa6863bc
+ depends on !RUST || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
config RISCV_ISA_ZBKB
bool "Zbkb extension support for bit manipulation instructions"
@@ -890,6 +904,20 @@ config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
versions of clang and GCC to be passed to GAS, which has the same result
as passing zicsr and zifencei to -march.
+config TOOLCHAIN_MATCHES_ZICSR_ZIFENCEI
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
+ depends on TOOLCHAIN_NEEDS_OLD_ISA_SPEC || !TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI || RUST_BINDGEN_LIBCLANG_VERSION >= 170000
+ help
+ LLVM/Clang >= 17.0.0 starts recognizing Zicsr/Zifencei in -march, passing
+ them to -march doesn't generate an error anymore, and passing them or not
+ doesn't have any real difference, it still follows ISA before version
+ 20190608 - Zicsr/Zifencei are included in base ISA.
+
+ The current latest version of LLVM/Clang still does not require explicit
+ Zicsr/Zifencei to enable these two extensions, Clang just accepts them in
+ -march and then silently ignores them.
+
config FPU
bool "FPU support"
default y
diff --git a/init/Kconfig b/init/Kconfig
index e3eb63eadc8757a10b091c74bbee8008278c0521..0859d308a48591df769c7dbaef6f035324892bd3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -82,6 +82,12 @@ config RUSTC_LLVM_VERSION
int
default $(rustc-llvm-version)
+config RUST_BINDGEN_LIBCLANG_VERSION
+ int
+ default $(rustc-bindgen-libclang-version)
+ help
+ This is the version of `libclang` used by the Rust bindings generator.
+
config CC_CAN_LINK
bool
default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
diff --git a/rust/Makefile b/rust/Makefile
index bfa915b0e58854045b367557342727fee4fe2808..8c6f84487c41880816d1e55ba4c0df0e5af4e8fd 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -290,20 +290,25 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
-fno-inline-functions-called-once -fsanitize=bounds-strict \
-fstrict-flex-arrays=% -fmin-function-alignment=% \
-fzero-init-padding-bits=% -mno-fdpic \
- --param=% --param asan-%
+ --param=% --param asan-% -mno-riscv-attribute
# 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_loongarch := loongarch64-linux-gnusf
+BINDGEN_TARGET_riscv := riscv64-linux-gnu
BINDGEN_TARGET_um := $(BINDGEN_TARGET_$(SUBARCH))
BINDGEN_TARGET := $(BINDGEN_TARGET_$(SRCARCH))
+ifeq ($(BINDGEN_TARGET),)
+$(error add '--target=' option to rust/Makefile)
+else
# All warnings are inhibited since GCC builds are very experimental,
# many GCC warnings are not supported by Clang, they may only appear in
# some configurations, with new GCC versions, etc.
bindgen_extra_c_flags = -w --target=$(BINDGEN_TARGET)
+endif
# Auto variable zero-initialization requires an additional special option with
# clang that is going to be removed sometime in the future (likely in
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index 33193ca6e8030e659d6b321acaea1acd42c387a4..b893bbc130f774bdca831893fed9b76d42bf540a 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -67,6 +67,7 @@ m64-flag := $(cc-option-bit,-m64)
rustc-version := $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC))
rustc-llvm-version := $(shell,$(srctree)/scripts/rustc-llvm-version.sh $(RUSTC))
+rustc-bindgen-libclang-version := $(shell,trap 'echo 0' EXIT; $(BINDGEN) $(srctree)/scripts/rust_is_available_bindgen_libclang.h 2>&1 | sed -nE 's:.*clang version ([0-9]+\.[0-9]+\.[0-9]+).*:\1:p' | awk -F'.' '{print $1 * 10000 + $2 * 100 + $3}')
# $(rustc-option,<flag>)
# Return y if the Rust compiler supports <flag>, n otherwise
---
base-commit: f777d1112ee597d7f7dd3ca232220873a34ad0c8
change-id: 20250914-gcc-rust-v3-a4154a826045
Best regards,
--
Asuna Yang <SpriteOvO@...il.com>
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