Re: [PATCH] arm64: Fix multiple 'asm-operand-widths' warnings
From: Matthias Kaehlcke
Date: Tue May 02 2017 - 13:26:24 EST
El Tue, May 02, 2017 at 11:27:18AM +0100 Mark Rutland ha dit:
> On Mon, May 01, 2017 at 02:26:22PM -0700, Matthias Kaehlcke wrote:
> > clang raises 'asm-operand-widths' warnings in inline assembly code when
> > the size of an operand is < 64 bits and the operand width is unspecified.
> > Most warnings are raised in macros, i.e. the datatype of the operand may
> > vary. Forcing the use of an x register through the 'x' operand modifier
> > would silence the warning however it involves the risk that for operands
> > < 64 bits 'unused' bits may be assigned to 64-bit values (more details at
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/503816.html).
> > Instead we cast the operand to 64 bits, which also forces the use of a
> > x register, but without the unexpected behavior.
> > In gic_write_bpr1() use write_sysreg_s() to write the register. This
> > aligns the functions with others in this header and fixes an
> > 'asm-operand-widths' warning.
> > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> > ---
> > arch/arm64/include/asm/arch_gicv3.h | 2 +-
> > arch/arm64/include/asm/barrier.h | 2 +-
> > arch/arm64/include/asm/uaccess.h | 2 +-
> > arch/arm64/kernel/armv8_deprecated.c | 2 +-
> > 4 files changed, 4 insertions(+), 4 deletions(-)
> Thanks for putting this together.
> Just to check, are these the only instances that you see clang warning
Yes, these are the only warnings clang raises in my builds (custom and
> There are a number of other cases where we can see similar problems
> (e.g. passing a u8 value to an smp_store_release() on a u32 variable),
> so we need to fix more than the clang warnings.
> I'm currently attempting a systematic audit of our inline asm to correct
> all instances, looking at:
> git grep -e asm \
> --and --not -e 'include' \
> --and --not -e 'asmlinkage' \
> -- arch/arm64
> I hope to have patches shortly, and will keep you informed.