[0/6] arm64: gcc asm flag outputs

Message

Richard Henderson March 11, 2020, 6:04 p.m. UTC

With gcc 10, arm64 includes support for flag outputs, much like
x86 has done for years.

The most effective use of this within the kernel is in uaccess,
where we can branch directly on the Carry flag output, e.g.

	adds    x3, x2, #0x2
	csel    x1, xzr, x1, hi
	csinv   x3, x3, xzr, cc
	sbcs    xzr, x3, x1
	b.ls    ffff800010084b5c <aarch32_break_handler+0xec>

Changing __arm64_rndr has very few uses, and so the effect is
very minor, but is also changed for consistency.

Finally, a mostly unrelated fix to uaccess.h, which I noticed
while poking around the header and looking at the assembly.
Has no effect on generic kernels that include ARMv8.3 support,
but eliminates a branch if one starts to play with the knobs.


r~


Richard Henderson (6):
  arm64: Add asm/ccset.h header
  arm64: uaccess: Use named asm operands for __in_range
  arm64: uaccess: Untie the input address in __range_ok
  arm64: uaccess: Use asm/ccset.h macros in __range_ok
  arm64: archrandom: Use asm/ccset.h macros in __arm64_rndr
  arm64: Hoist CONFIG option out of ALTERNATIVE in uaccess.h

 arch/arm64/include/asm/archrandom.h |  7 +++--
 arch/arm64/include/asm/ccset.h      | 19 ++++++++++++
 arch/arm64/include/asm/uaccess.h    | 46 ++++++++++++++++-------------
 3 files changed, 48 insertions(+), 24 deletions(-)
 create mode 100644 arch/arm64/include/asm/ccset.h