[PATCH] riscv: avoid enabling vectorized code generation

From: Saleem Abdulrasool <abdulras@google.com>
To: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	 Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	 Saleem Abdulrasool <abdulras@google.com>
Subject: [PATCH] riscv: avoid enabling vectorized code generation
Date: Fri, 16 Dec 2022 18:50:12 +0000	[thread overview]
Message-ID: <20221216185012.2342675-1-abdulras@google.com> (raw)

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@google.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


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