linux-kernel - [PATCH] riscv: avoid enabling vectorized code generation

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Date:   Fri, 16 Dec 2022 18:50:12 +0000
From:   Saleem Abdulrasool <abdulras@...gle.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Saleem Abdulrasool <abdulras@...gle.com>
Subject: [PATCH] riscv: avoid enabling vectorized code generation

The compiler is free to generate vectorized operations for zero'ing
memory.  The kernel does not use the vector unit on RISCV, similar to
architectures such as x86 where we use `-mno-mmx` et al to prevent the
implicit vectorization.  Perform a similar check for
`-mno-implicit-float` to avoid this on RISC-V targets.

Signed-off-by: Saleem Abdulrasool <abdulras@...gle.com>
---
 arch/riscv/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 0d13b597cb55..68433476a96e 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -89,6 +89,10 @@ KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
 # architectures.  It's faster to have GCC emit only aligned accesses.
 KBUILD_CFLAGS += $(call cc-option,-mstrict-align)
 
+# Ensure that we do not vectorize the kernel code when the `v` extension is
+# enabled.  This mirrors the `-mno-mmx` et al on x86.
+KBUILD_CFLAGS += $(call cc-option,-mno-implicit-float)
+
 ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
 prepare: stack_protector_prepare
 stack_protector_prepare: prepare0
-- 
2.39.0.314.g84b9a713c41-goog