2023-12-08 05:55:35

by Samuel Holland

Subject: [RFC PATCH 04/12] arm64: Implement ARCH_HAS_KERNEL_FPU_SUPPORT

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.

Signed-off-by: Samuel Holland <[email protected]>
---

arch/arm64/Kconfig | 1 +
arch/arm64/Makefile | 9 ++++++++-
arch/arm64/include/asm/fpu.h | 17 +++++++++++++++++
3 files changed, 26 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/include/asm/fpu.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b071a00425d..485ac389ac11 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 9a2d3723cd0f..4a65f24c7998 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..664c0a192ab1
--- /dev/null
+++ b/arch/arm64/include/asm/fpu.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * linux/arch/arm64/include/asm/fpu.h
+ *
+ * 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 */
--
2.42.0

2023-12-11 16:52:53

by Christoph Hellwig

Subject: Re: [RFC PATCH 04/12] arm64: Implement ARCH_HAS_KERNEL_FPU_SUPPORT

> + * linux/arch/arm64/include/asm/fpu.h

Same comment as for arm here. Except for that:

Reviewed-by: Christoph Hellwig <[email protected]>

2023-12-13 16:20:43

by Will Deacon

Subject: Re: [RFC PATCH 04/12] arm64: Implement ARCH_HAS_KERNEL_FPU_SUPPORT

On Thu, Dec 07, 2023 at 09:54:34PM -0800, Samuel Holland wrote:
> 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.
>
> Signed-off-by: Samuel Holland <[email protected]>
> ---
>
> arch/arm64/Kconfig | 1 +
> arch/arm64/Makefile | 9 ++++++++-
> arch/arm64/include/asm/fpu.h | 17 +++++++++++++++++
> 3 files changed, 26 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/include/asm/fpu.h
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7b071a00425d..485ac389ac11 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 9a2d3723cd0f..4a65f24c7998 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)

Can you use this to replace the same logic in arch/arm64/lib/Makefile,
like you do for arch/arm/?

Will