On Mon, 3 Dec 2018 at 20:22, Will Deacon [off-list ref] wrote:

On Wed, Nov 28, 2018 at 09:09:00AM +0800, Jackie Liu wrote:

quoted

In a way similar to ARM commit 09096f6a0ee2 ("ARM: 7822/1: add workaround
for ambiguous C99 stdint.h types"), this patch redefines the macros that
are used in stdint.h so its definitions of uint64_t and int64_t are
compatible with those of the kernel.

This patch comes from: https://patchwork.kernel.org/patch/3540001/
Wrote by: Ard Biesheuvel [off-list ref]

We mark this file as a private file and don't have to override asm/types.h

Reviewed-by: Ard Biesheuvel <redacted>
Signed-off-by: Jackie Liu <redacted>
---
 arch/arm64/include/asm/neon-intrinsics.h | 34 ++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 arch/arm64/include/asm/neon-intrinsics.h

diff --git a/arch/arm64/include/asm/neon-intrinsics.h b/arch/arm64/include/asm/neon-intrinsics.h
new file mode 100644
index 0000000..e378766
--- /dev/null
+++ b/arch/arm64/include/asm/neon-intrinsics.h

@@ -0,0 +1,34 @@
+#ifndef _NEON_INTRINSICS_H
+#define _NEON_INTRINSICS_H

We tend to name these with an __ASM_ prefix, so it should be:

#ifndef __ASM_NEON_INTRINSICS_H

That said, I notice that the commit you refer to for arch/arm/ actually
places this stuff under uapi/. Is that needed?

No, it doesn't. It creates asm/types.h which has been moved into uap/
at a later date (which I guess means we're stuck with it). In
hindsight, it would have been better for ARM to create a neon
instrinsics header file such as this one, since the override is only
needed when you include <arm_neon.h>.

quoted

+#include <asm-generic/int-ll64.h>
+
+/*
+ * For Aarch64, there is some ambiguity in the definition of the types below
+ * between the kernel and GCC itself. This is usually not a big deal, but it
+ * causes trouble when including GCC's version of 'stdint.h' (this is the file
+ * that gets included when you #include <stdint.h> on a -ffreestanding build).
+ * As this file also gets included implicitly when including 'arm_neon.h' (the
+ * NEON intrinsics support header), we need the following to work around the
+ * issue if we want to use NEON intrinsics in the kernel.
+ */

Could you elaborate on what the ambiguities / conflicts in the types are
please? I think you can also remove the sentence about directly including
stdint on a freestanding build, since it doesn't seem relevant to the
kernel afaict (we only pull it in via arm_neon.h).

In the kernel, u64/s64 are [un]signed long long, not [un]signed long.
So by redefining these macros to the former, we can force gcc-stdint.h
to define uint64_t / in64_t in a compatible manner.

quoted

+
+#ifdef __INT64_TYPE__
+#undef __INT64_TYPE__
+#define __INT64_TYPE__               __signed__ long long

Do we need this __signed__ part?

No that seems redundant to me.