On Thu, May 14, 2020 at 07:14:58AM +0530, Anshuman Khandual wrote:
> On 05/13/2020 08:34 PM, Dave Martin wrote:
> > On Thu, May 07, 2020 at 06:59:10PM +0530, Anshuman Khandual wrote:
> >> diff --git a/arch/arm64/include/asm/hwcap.h
> >> b/arch/arm64/include/asm/hwcap.h
> >> index 0f00265248b5..589ac02e1ddd 100644
> >> --- a/arch/arm64/include/asm/hwcap.h
> >> +++ b/arch/arm64/include/asm/hwcap.h
> >> @@ -8,18 +8,27 @@
> >> #include <uapi/asm/hwcap.h>
> >> #include <asm/cpufeature.h>
> >>
> >> +#define COMPAT_HWCAP_SWP (1 << 0)
> >> #define COMPAT_HWCAP_HALF (1 << 1)
> >> #define COMPAT_HWCAP_THUMB (1 << 2)
> >> +#define COMPAT_HWCAP_26BIT (1 << 3)
> >> #define COMPAT_HWCAP_FAST_MULT (1 << 4)
> >> +#define COMPAT_HWCAP_FPA (1 << 5)
> >> #define COMPAT_HWCAP_VFP (1 << 6)
> >> #define COMPAT_HWCAP_EDSP (1 << 7)
> >> +#define COMPAT_HWCAP_JAVA (1 << 8)
> >> +#define COMPAT_HWCAP_IWMMXT (1 << 9)
> >> +#define COMPAT_HWCAP_CRUNCH (1 << 10)
> >> +#define COMPAT_HWCAP_THUMBEE (1 << 11)
> >> #define COMPAT_HWCAP_NEON (1 << 12)
> >> #define COMPAT_HWCAP_VFPv3 (1 << 13)
> >> +#define COMPAT_HWCAP_VFPV3D16 (1 << 14)
> >> #define COMPAT_HWCAP_TLS (1 << 15)
> >> #define COMPAT_HWCAP_VFPv4 (1 << 16)
> >> #define COMPAT_HWCAP_IDIVA (1 << 17)
> >> #define COMPAT_HWCAP_IDIVT (1 << 18)
> >> #define COMPAT_HWCAP_IDIV (COMPAT_HWCAP_IDIVA|COMPAT_HWCAP_IDIVT)
> >> +#define COMPAT_HWCAP_VFPD32 (1 << 19)
> >> #define COMPAT_HWCAP_LPAE (1 << 20)
> >> #define COMPAT_HWCAP_EVTSTRM (1 << 21)
> >
> > With the possible exception of SWP (does the swp emulation allow us to
> > report this as supported?), I think all these weren't mentioned because
> > they aren't included in ARMv8 and so can never be reported.
> >
> > If we find ourselves reporting them, there's a bug somewhere.
> >
> > So, can we just default all obsolete string entries to NULL?
> >
> > When generating the cpuinfo strings we could WARN and just emit an empty
> > string for that hwcap.
>
> All these above will be a change in the existing user visible behavior on
> the system and this patch never intended to create one.
Why is it a change? We've never reported e.g. "java" on an arm64 kernel, so
I agree with Dave that we shouldn't be adding this string. If it /ever/ ends
up in userspace it's because something has gone horribly wrong. NULL would
be much better. Couldn't you achieve that by simply omitting these entries?
e.g. deleting things like:
[COMPAT_KERNEL_HWCAP(JAVA)] = "java",
completely (including the COMPAT_HWCAP_JAVA definition)?
> Hence, I will just defer this to maintainers on whether we should change
> existing /proc/cpuinfo output (including non-practically-possible ones on
> ARMv8) or even treat swap emulation as SWP.
SWP is fine because we emulate it and so userspace can use it. Removing that
*would* be a change in behaviour. I don't think the compat ABI is broken
here, so please don't change it without good reason.
Will
