[PATCH] arm64: add workaround for ambiguous C99 stdint.h types

[Ard Biesheuvel]

On 17 February 2014 19:17, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> On 17 February 2014 19:02, Catalin Marinas <catalin.marinas at arm.com> wrote:
>> On Mon, Feb 17, 2014 at 05:57:22PM +0000, Ard Biesheuvel wrote:
>>> On 17 February 2014 18:42, Catalin Marinas <catalin.marinas at arm.com> wrote:
[...]
>>> > For other intrinsics that we use like __builtin_ctzl(), do we need to
>>> > explicitly include gcc headers? I don't think we do and I really don't
>>> > like such arm_neon.h include which brings in other user headers. Don't
>>> > we have any work around this?
>>>
>>> Well, I talked to the toolchain guys at the time and they really
>>> disliked the idea of coding directly against the __builtins because
>>> they are not considered a stable interface, especially because the
>>> interface that /is/ considered stable (arm_neon.h) is supported both
>>> on ARM and on arm64.
>>
>> Than we don't use the Neon __builtins in the kernel.
>>
>>> > My inbox only has some discussion in May last year on the linaro-kernel
>>> > list without any clear conclusion (it could be that I deleted other
>>> > emails).
>>>
>>> There was some discussion, indeed, but for ARM, with the conclusion
>>> being the fix I mentioned in the patch: 09096f6a0ee2 ("ARM: 7822/1:
>>> add workaround
>>> for ambiguous C99 stdint.h types"), only in that case, the ambiguity
>>> is (unsurprisingly) about the 32 bit types, not the 64 bit ones.
>>
>> My worry is that some future toolchain may include something else in
>> this file and get other type conflicts. It really looks fragile.
>>
>
> Well, the GCC folks are quite careful not to depend on arbitrary user
> headers when the -ffreestanding option is set. Also, the real problem
> is the fact that Linux defines C99 types, but does so in an
> incompatible way. (I.e., one could also argue that the Linux typedefs
> should be based on GCC's builtin #defines of __INT64_TYPE,
> __UINT64_TYPE, etc if defined). So the chances of something similar
> reappearing all of a sudden are quite slim imo.
>

Perhaps this alternative approach would be better?

diff --git a/include/linux/types.h b/include/linux/types.h
index 4d118ba11349..78344874fff0 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -108,9 +108,9 @@ typedef             __u16           uint16_t;
 typedef                __u32           uint32_t;

 #if defined(__GNUC__)
-typedef                __u64           uint64_t;
-typedef                __u64           u_int64_t;
-typedef                __s64           int64_t;
+typedef                __UINT64_TYPE__ uint64_t;
+typedef                __UINT64_TYPE__ u_int64_t;
+typedef                __INT64_TYPE__  int64_t;
 #endif

I mean, we are already depending explicitly on __GNUC__, and GNUC
tells us exactly which types it thinks should be used for typedef'ing
[u]int64_t.

Anyway, I am perfectly happy to park this until a real use case shows
up. I have some crypto coded up in intrinsics, but we won't know if
it's fast enough until I manage to run it on actual hardware.

Regards,
Ard.