[PATCH v4 04/15] arm64: Implement ARCH_HAS_KERNEL_FPU_SUPPORT

From: Samuel Holland
Date: Fri Mar 29 2024 - 03:25:37 EST


arm64 provides an equivalent to the common kernel-mode FPU API, but in a
different header and using different function names. Add a wrapper
header, and export CFLAGS adjustments as found in lib/raid6/Makefile.

Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
---

(no changes since v2)

Changes in v2:
- Remove file name from header comment

arch/arm64/Kconfig | 1 +
arch/arm64/Makefile | 9 ++++++++-
arch/arm64/include/asm/fpu.h | 15 +++++++++++++++
3 files changed, 24 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/include/asm/fpu.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b11c98b3e84..67f0d3b5b7df 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -30,6 +30,7 @@ config ARM64
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_GIGANTIC_PAGE
select ARCH_HAS_KCOV
+ select ARCH_HAS_KERNEL_FPU_SUPPORT if KERNEL_MODE_NEON
select ARCH_HAS_KEEPINITRD
select ARCH_HAS_MEMBARRIER_SYNC_CORE
select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 0e075d3c546b..3e863e5b0169 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -36,7 +36,14 @@ ifeq ($(CONFIG_BROKEN_GAS_INST),y)
$(warning Detected assembler with broken .inst; disassembly will be unreliable)
endif

-KBUILD_CFLAGS += -mgeneral-regs-only \
+# The GCC option -ffreestanding is required in order to compile code containing
+# ARM/NEON intrinsics in a non C99-compliant environment (such as the kernel)
+CC_FLAGS_FPU := -ffreestanding
+# Enable <arm_neon.h>
+CC_FLAGS_FPU += -isystem $(shell $(CC) -print-file-name=include)
+CC_FLAGS_NO_FPU := -mgeneral-regs-only
+
+KBUILD_CFLAGS += $(CC_FLAGS_NO_FPU) \
$(compat_vdso) $(cc_has_k_constraint)
KBUILD_CFLAGS += $(call cc-disable-warning, psabi)
KBUILD_AFLAGS += $(compat_vdso)
diff --git a/arch/arm64/include/asm/fpu.h b/arch/arm64/include/asm/fpu.h
new file mode 100644
index 000000000000..2ae50bdce59b
--- /dev/null
+++ b/arch/arm64/include/asm/fpu.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 SiFive
+ */
+
+#ifndef __ASM_FPU_H
+#define __ASM_FPU_H
+
+#include <asm/neon.h>
+
+#define kernel_fpu_available() cpu_has_neon()
+#define kernel_fpu_begin() kernel_neon_begin()
+#define kernel_fpu_end() kernel_neon_end()
+
+#endif /* ! __ASM_FPU_H */
--
2.44.0