[PATCH 0/4] ABI updates

Tony Lindgren tony at atomide.com
Mon Jul 7 04:19:48 PDT 2014

* Russell King - ARM Linux <linux at arm.linux.org.uk> [140704 12:56]:
> As a result of the recent discussions about android, several issues
> have been identified with existing kernels:
> 1. HWCAP_SWP does not properly reflect whether the SWP instruction
>    should be used.  Turn HWCAP_SWP off on ARMv6+ where the exclusives
>    are available.
> 2. SWP is unsafe when running on a SMP CPU; there is no bus locking
>    between the read and write parts of the instruction execution.
>    Force SWP emulation on ARMv7+ where we can disable the SWP
>    instruction.
> 3. Reporting of alignment faults - kernel mode faults are silent due to
>    the requirements of the network stack, but we can note where the
>    last one occurs.
> Testing reveals that at least my OMAP4430 userspace (supplied from TI)
> executes lots of SWP instructions, which is something that wasn't known
> before this patch.
> Many systems today are not configured with SWP emulation enabled on SMP.
> This means that the SWP instruction is available, but unsafe.
>  arch/arm/kernel/setup.c       | 29 ++++++++++++++++++++++-------
>  arch/arm/kernel/swp_emulate.c |  4 ++++
>  arch/arm/mm/Kconfig           |  2 +-
>  arch/arm/mm/alignment.c       |  4 +++-
>  4 files changed, 30 insertions(+), 9 deletions(-)

Tried testing this on omap2 which is ARMv6 with no K, but got this:

arch/arm/kernel/setup.c: In function ‘elf_hwcap_fixup’:
arch/arm/kernel/setup.c:405:2: error: implicit declaration of function ‘read_cpuid_part’ [-Werror=implicit-function-declaration]

That should be read_cpuid_part_number instead. After fixing that,
omap2 booted fine, so for ARMv6 with no K:

Tested-by: Ton Lindgren <tony at atomide.com>

More information about the linux-arm-kernel mailing list