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Message-ID: <87v7gk8r5x.fsf@posteo.net>
Date: Thu, 29 Jan 2026 13:49:56 +0000
From: Charalampos Mitrodimas <charmitro@...teo.net>
To: Asuna Yang <xinrui.riscv@...c.iscas.ac.cn>
Cc: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nsc@...nel.org>,
Miguel Ojeda <ojeda@...nel.org>, 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>, Nick
Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling
<morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, Paul Walmsley
<pjw@...nel.org>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou
<aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>, Jonathan
Corbet <corbet@....net>, Conor Dooley <conor@...nel.org>, Mingcong Bai
<jeffbai@...c.io>, Han Gao <rabenda.cn@...il.com>, Vivian Wang
<wangruikang@...as.ac.cn>, Jason Montleon <jmontleo@...hat.com>,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
rust-for-linux@...r.kernel.org, llvm@...ts.linux.dev,
linux-riscv@...ts.infradead.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 4/4] RISC-V: handle extension configs for bindgen,
re-enable gcc + rust builds
Asuna Yang <xinrui.riscv@...c.iscas.ac.cn> writes:
> Commit 33549fcf37ec ("RISC-V: disallow gcc + rust builds") disabled GCC
> + Rust builds for RISC-V due to differences in extension handling
> compared to LLVM. This commit enables GCC + Rust builds again.
>
> Add `bindgen-option` 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'.
>
> Update the documentation, GCC + Rust builds for RISC-V are now
> maintained.
>
> Acked-by: Miguel Ojeda <ojeda@...nel.org>
> Signed-off-by: Asuna Yang <xinrui.riscv@...c.iscas.ac.cn>
> ---
> Documentation/rust/arch-support.rst | 2 +-
> arch/riscv/Kconfig | 35 ++++++++++++++++++++++++++++++++++-
> rust/Makefile | 3 ++-
> scripts/Makefile.rust | 1 +
> 4 files changed, 38 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 6b39f37f769a..c869ee07117e 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 && TOOLCHAIN_MATCHES_ZICSR_ZIFENCEI
> select HAVE_SAMPLE_FTRACE_DIRECT
> select HAVE_SAMPLE_FTRACE_DIRECT_MULTI
> select HAVE_STACKPROTECTOR
> @@ -619,6 +619,8 @@ config TOOLCHAIN_HAS_V
> depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32imv)
> depends on LD_IS_LLD || LD_VERSION >= 23800
> depends on AS_HAS_OPTION_ARCH
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64imv)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32imv)
Hi Asuna!
I'm under the impression that the `!RUST ||` guard here doesn't
actually prevent the `$(bindgen-backend-option,...)` call from being
executed. `$(...)` shell expansions should happen during the textual
substitution phase, before symbol dependency evaluation occurs, check
documentation at kconfig-macro-language.rst lines 228-229.
I did this test:
$ cat /tmp/fake_bindgen
#!/bin/bash
echo "[BINDGEN INVOKED] $(date '+%H:%M:%S') args: $@" >> /tmp/bindgen_calls.log
# Call real bindgen
exec /home/charmitro/.cargo/bin/bindgen "$@"
$ make ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- BINDGEN=/tmp/fake_bindgen defconfig
HOSTCC scripts/basic/fixdep
...
*** Default configuration is based on 'defconfig'
#
# configuration written to .config
#
$ linux git:(master) rg CONFIG_RUST .config
...
283:# CONFIG_RUST is not set
...
$ cat /tmp/bindgen_calls.log
[BINDGEN INVOKED] 15:44:44 args: --version workaround-for-0.69.0
[BINDGEN INVOKED] 15:44:44 args: ./scripts/rust_is_available_bindgen_libclang.h
[BINDGEN INVOKED] 15:44:44 args: --version workaround-for-0.69.0
[BINDGEN INVOKED] 15:44:44 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64imv
[BINDGEN INVOKED] 15:44:44 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32imv
[BINDGEN INVOKED] 15:44:44 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zabha
[BINDGEN INVOKED] 15:44:44 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zabha
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zacas
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zacas
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zbb
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zbb
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zba
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zba
[BINDGEN INVOKED] 15:44:45 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zbc
[BINDGEN INVOKED] 15:44:46 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zbc
[BINDGEN INVOKED] 15:44:46 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zbkb
[BINDGEN INVOKED] 15:44:46 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zbkb
[BINDGEN INVOKED] 15:44:46 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=lp64 -march=rv64ima_zicsr_zifencei
[BINDGEN INVOKED] 15:44:46 args: /dev/null -- -x c --target=riscv64-linux-gnu -mabi=ilp32 -march=rv32ima_zicsr_zifencei
So, CONFIG_RUST not set, yet bindgen was invoked. Not sure if that is
intentional though.
Cheers,
C. Mitrodimas
>
> config RISCV_ISA_V
> bool "Vector extension support"
> @@ -683,6 +685,8 @@ 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
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zabha)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zabha)
>
> config RISCV_ISA_ZABHA
> bool "Zabha extension support for atomic byte/halfword operations"
> @@ -701,6 +705,8 @@ 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
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zacas)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zacas)
>
> config RISCV_ISA_ZACAS
> bool "Zacas extension support for atomic CAS"
> @@ -719,6 +725,8 @@ config TOOLCHAIN_HAS_ZBB
> depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbb)
> depends on LD_IS_LLD || LD_VERSION >= 23900
> depends on AS_HAS_OPTION_ARCH
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zbb)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zbb)
>
> # 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.
> @@ -734,6 +742,8 @@ config TOOLCHAIN_HAS_ZBA
> depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zba)
> depends on LD_IS_LLD || LD_VERSION >= 23900
> depends on AS_HAS_OPTION_ARCH
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zba)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zba)
>
> config RISCV_ISA_ZBA
> bool "Zba extension support for bit manipulation instructions"
> @@ -769,6 +779,8 @@ config TOOLCHAIN_HAS_ZBC
> depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbc)
> depends on LD_IS_LLD || LD_VERSION >= 23900
> depends on AS_HAS_OPTION_ARCH
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zbc)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zbc)
>
> config RISCV_ISA_ZBC
> bool "Zbc extension support for carry-less multiplication instructions"
> @@ -792,6 +804,8 @@ config TOOLCHAIN_HAS_ZBKB
> depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbkb)
> depends on LD_IS_LLD || LD_VERSION >= 23900
> depends on AS_HAS_OPTION_ARCH
> + depends on !RUST || !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zbkb)
> + depends on !RUST || !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zbkb)
>
> config RISCV_ISA_ZBKB
> bool "Zbkb extension support for bit manipulation instructions"
> @@ -893,6 +907,25 @@ 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_HAS_ZICSR_ZIFENCEI
> + def_bool y
> + depends on !64BIT || $(bindgen-backend-option,-mabi=lp64 -march=rv64ima_zicsr_zifencei)
> + depends on !32BIT || $(bindgen-backend-option,-mabi=ilp32 -march=rv32ima_zicsr_zifencei)
> +
> +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_HAS_ZICSR_ZIFENCEI
> + 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/rust/Makefile b/rust/Makefile
> index 37b4205afb70..d8b6a570cb84 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -383,7 +383,8 @@ 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-% -fno-isolate-erroneous-paths-dereference
> + --param=% --param asan-% -fno-isolate-erroneous-paths-dereference \
> + -mno-riscv-attribute
>
> # Because scripts/Makefile.rust is included regardless of whether Rust is enabled,
> # we perform this check here to avoid breaking targets that do not yet support Rust builds.
> diff --git a/scripts/Makefile.rust b/scripts/Makefile.rust
> index 5c12b4b8c8b6..bfdad4a0a3ce 100644
> --- a/scripts/Makefile.rust
> +++ b/scripts/Makefile.rust
> @@ -3,6 +3,7 @@ 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))
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