On Thu, May 22, 2025 at 2:02 PM Rudraksha Gupta guptarud@gmail.com wrote:
Currently rust on arm fails to compile due to '-mno-fdpic'. This flag disables a GCC feature that we don't want for kernel builds, so let's skip it as it doesn't apply to Clang.
UPD include/generated/asm-offsets.h CALL scripts/checksyscalls.sh RUSTC L rust/core.o BINDGEN rust/bindings/bindings_generated.rs BINDGEN rust/bindings/bindings_helpers_generated.rs CC rust/helpers/helpers.o Unable to generate bindings: clang diagnosed error: error: unknown argument: '-mno-fdpic' make[2]: *** [rust/Makefile:369: rust/bindings/bindings_helpers_generated.rs] Error 1 make[2]: *** Deleting file 'rust/bindings/bindings_helpers_generated.rs' make[2]: *** Waiting for unfinished jobs.... Unable to generate bindings: clang diagnosed error: error: unknown argument: '-mno-fdpic' make[2]: *** [rust/Makefile:349: rust/bindings/bindings_generated.rs] Error 1 make[2]: *** Deleting file 'rust/bindings/bindings_generated.rs' make[1]: *** [/home/pmos/build/src/linux-next-next-20250521/Makefile:1285: prepare] Error 2 make: *** [Makefile:248: __sub-make] Error 2Reported-by: Linux Kernel Functional Testing lkft@linaro.org Closes: https://lore.kernel.org/all/CA+G9fYvOanQBYXKSg7C6EU30k8sTRC0JRPJXYu7wWK51w38... Suggested-by: Miguel Ojeda ojeda@kernel.org Tested-by: Rudraksha Gupta guptarud@gmail.com Acked-by: Naresh Kamboju naresh.kamboju@linaro.org Signed-off-by: Rudraksha Gupta guptarud@gmail.com
Applied to `rust-next` -- thanks everyone!
[ Naresh provided the draft diff [1].
Ben explained [2]:
FDPIC is only relevant with no-MMU targets, and then only for userspace. When configured for the arm-*-uclinuxfdpiceabi target, GCC enables FDPIC by default to facilitate compiling userspace programs. FDPIC is never used for the kernel, and we pass -mno-fdpic when building the kernel to override the default and make sure FDPIC is disabled.
and [3]:
-mno-fdpic disables a GCC feature that we don't want for kernel builds. clang does not support this feature, so it always behaves as though -mno-fdpic is passed. Therefore, it should be fine to mix the two, at least as far as FDPIC is concerned.
[1] https://lore.kernel.org/rust-for-linux/CA+G9fYt4otQK4pHv8pJBW9e28yHSGCDncKqu... [2] https://lore.kernel.org/rust-for-linux/aAKrq2InExQk7f_k@dell-precision-5540/ [3] https://lore.kernel.org/rust-for-linux/aAo_F_UP1Gd4jHlZ@dell-precision-5540/
- Miguel ]
[ Reworded title. - Miguel ]
Cheers, Miguel