Messages in this thread Patch in this message | | | Date | Tue, 5 May 2020 19:42:43 +0200 | From | Torsten Duwe <> | Subject | Re: [PATCH] arm64: disable patchable function entry on big-endian clang builds |
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Hi Arnd, Mark and others,
this may not be worth arguing but I'm currently fighting excessive workarounds in another area and so this triggers me, so I have to make a remark ;-)
On Tue, 5 May 2020 15:25:56 +0100 Mark Rutland <mark.rutland@arm.com> wrote:
> On Tue, May 05, 2020 at 04:12:36PM +0200, Arnd Bergmann wrote: > > Clang only supports the patchable_function_entry attribute on > > little-endian arm64 builds, but not on big-endian: > > > > include/linux/kasan-checks.h:16:8: error: unknown attribute > > 'patchable_function_entry' ignored [-Werror,-Wunknown-attributes] > > > > Disable that configuration with another dependency. Unfortunately > > the existing check is not enough, as $(cc-option) at this point does > > not pass the -mbig-endian flag. > > Well that's unfortunate. :( > > Do we know if this is deliberate and/or likely to change in future? > This practically rules out a BE distro kernel with things like PAC, > which isn't ideal.
But still better than cumulating workarounds. If clang's flags aren't orthogonal then that's a bug in clang. If I get a vote here I'm against it.
> > Fixes: 3b23e4991fb6 ("arm64: implement ftrace with regs") > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > This looks fine for now, and we can add a version check in future, so: ^^^^^^^^^^^^^^^^^^^ see what I mean? And in the end another line of code you'll never again get rid of.
I suggest to get a quote from clang folks first about their schedule and regarded importance of patchable-function-entries on BE, and leave it as is: broken on certain clang configurations. It's not the kernel's fault.
> Acked-by: Mark Rutland <mark.rutland@arm.com> > > Mark. > > > --- > > arch/arm64/Kconfig | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > index 4b256fa6db7a..a33d6402b934 100644 > > --- a/arch/arm64/Kconfig > > +++ b/arch/arm64/Kconfig > > @@ -151,7 +151,7 @@ config ARM64 > > select HAVE_DMA_CONTIGUOUS > > select HAVE_DYNAMIC_FTRACE > > select HAVE_DYNAMIC_FTRACE_WITH_REGS \ > > - if $(cc-option,-fies on y=2) > > + if $(cc-option,-fpatchable-function-entry=2) && > > !(CC_IS_CLANG && CPU_BIG_ENDIAN) select > > HAVE_EFFICIENT_UNALIGNED_ACCESS select HAVE_FAST_GUP > > select HAVE_FTRACE_MCOUNT_RECORD > > -- > > 2.26.0 > >
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