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Message-ID: <20250903190806.2604757-2-SpriteOvO@gmail.com>
Date: Wed, 3 Sep 2025 21:07:57 +0200
From: Asuna Yang <spriteovo@...il.com>
To: Conor Dooley <conor@...nel.org>,
Jason Montleon <jmontleo@...hat.com>,
Han Gao <rabenda.cn@...il.com>,
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>,
Masahiro Yamada <masahiroy@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
Bill Wendling <morbo@...gle.com>,
Justin Stitt <justinstitt@...gle.com>,
Tejun Heo <tj@...nel.org>,
Kees Cook <kees@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Matthew Maurer <mmaurer@...gle.com>,
Jeff Xu <jeffxu@...omium.org>,
Shakeel Butt <shakeel.butt@...ux.dev>,
Jan Hendrik Farr <kernel@...rr.cc>,
Michal Koutný <mkoutny@...e.com>,
Christian Brauner <brauner@...nel.org>,
Brian Gerst <brgerst@...il.com>
Cc: 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 2/2] 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 non-visible symbol to ensure that all important RISC-V
specific flags that will be used by GCC can be correctly recognized by
Rust bindgen's libclang, otherwise config HAVE_RUST will not be
selected.
Signed-off-by: Asuna Yang <SpriteOvO@...il.com>
---
Documentation/rust/arch-support.rst | 2 +-
arch/riscv/Kconfig | 62 ++++++++++++++++++++++++++++-
rust/Makefile | 7 +++-
3 files changed, 68 insertions(+), 3 deletions(-)
diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
index 6e6a515d0899..5282e0e174e8 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 1c5544401530..d7f421e0f429 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -195,7 +195,7 @@ 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 && RUST_BINDGEN_LIBCLANG_RECOGNIZES_FLAGS
select HAVE_SAMPLE_FTRACE_DIRECT
select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
select HAVE_STACKPROTECTOR
@@ -236,6 +236,27 @@ config RUSTC_SUPPORTS_RISCV
# -Zsanitizer=shadow-call-stack flag.
depends on !SHADOW_CALL_STACK || RUSTC_VERSION >= 108200
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_FLAGS
+ def_bool y
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_V
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZABHA
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZACAS
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBA
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBB
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBC
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBKB
+ depends on RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZICSR_ZIFENCEI
+ help
+ Rust bindgen currently relies on libclang as backend. When a mixed build is
+ performed (building C code with GCC), GCC flags will be passed to libclang.
+ However, not all GCC flags are recognized by Clang, so most of the
+ incompatible flags have been filtered out in rust/Makefile.
+
+ For RISC-V, GCC and Clang are not at the same pace of implementing extensions.
+ This config ensures that all important RISC-V specific flags that will be
+ used by GCC can be correctly recognized by Rust bindgen's libclang, otherwise
+ config HAVE_RUST will not be selected.
+
config CLANG_SUPPORTS_DYNAMIC_FTRACE
def_bool CC_IS_CLANG
# https://github.com/ClangBuiltLinux/linux/issues/1817
@@ -634,6 +655,11 @@ config TOOLCHAIN_HAS_V
depends on LLD_VERSION >= 140000 || LD_VERSION >= 23800
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_V
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/e6de53b4de4aecca4ac892500a0907805896ed27
+ depends on !TOOLCHAIN_HAS_V || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
+
config RISCV_ISA_V
bool "Vector extension support"
depends on TOOLCHAIN_HAS_V
@@ -698,6 +724,11 @@ config TOOLCHAIN_HAS_ZABHA
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zabha)
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZABHA
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/6b7444964a8d028989beee554a1f5c61d16a1cac
+ depends on !TOOLCHAIN_HAS_ZABHA || RUST_BINDGEN_LIBCLANG_VERSION >= 190100
+
config RISCV_ISA_ZABHA
bool "Zabha extension support for atomic byte/halfword operations"
depends on TOOLCHAIN_HAS_ZABHA
@@ -716,6 +747,11 @@ config TOOLCHAIN_HAS_ZACAS
depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zacas)
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZACAS
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/614aeda93b2225c6eb42b00ba189ba7ca2585c60
+ depends on !TOOLCHAIN_HAS_ZACAS || RUST_BINDGEN_LIBCLANG_VERSION >= 200100
+
config RISCV_ISA_ZACAS
bool "Zacas extension support for atomic CAS"
depends on TOOLCHAIN_HAS_ZACAS
@@ -735,6 +771,11 @@ config TOOLCHAIN_HAS_ZBB
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBB
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/33d008b169f3c813a4a45da220d0952f795ac477
+ depends on !TOOLCHAIN_HAS_ZBB || 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.
# binutils added all except Zvkb, then added Zvkb. So we just check for Zvkb.
@@ -750,6 +791,11 @@ config TOOLCHAIN_HAS_ZBA
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBA
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/33d008b169f3c813a4a45da220d0952f795ac477
+ depends on !TOOLCHAIN_HAS_ZBA || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
+
config RISCV_ISA_ZBA
bool "Zba extension support for bit manipulation instructions"
default y
@@ -785,6 +831,11 @@ config TOOLCHAIN_HAS_ZBC
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBC
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/33d008b169f3c813a4a45da220d0952f795ac477
+ depends on !TOOLCHAIN_HAS_ZBC || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
+
config RISCV_ISA_ZBC
bool "Zbc extension support for carry-less multiplication instructions"
depends on TOOLCHAIN_HAS_ZBC
@@ -808,6 +859,11 @@ config TOOLCHAIN_HAS_ZBKB
depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
depends on AS_HAS_OPTION_ARCH
+config RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZBKB
+ def_bool y
+ # https://github.com/llvm/llvm-project/commit/7ee1c162cc53d37f717f9a138276ad64fa6863bc
+ depends on !TOOLCHAIN_HAS_ZBKB || RUST_BINDGEN_LIBCLANG_VERSION >= 140000
+
config RISCV_ISA_ZBKB
bool "Zbkb extension support for bit manipulation instructions"
depends on TOOLCHAIN_HAS_ZBKB
@@ -894,6 +950,10 @@ 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 RUST_BINDGEN_LIBCLANG_RECOGNIZES_ZICSR_ZIFENCEI
+ def_bool y
+ depends on TOOLCHAIN_NEEDS_OLD_ISA_SPEC || (TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI && RUST_BINDGEN_LIBCLANG_VERSION >= 170000)
+
config FPU
bool "FPU support"
default y
diff --git a/rust/Makefile b/rust/Makefile
index 34d0429d50fd..7b1055c98146 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -277,20 +277,25 @@ 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
--
2.51.0
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