Hi Anisse, Dave, On Fri, Jun 14, 2019 at 01:22:22PM +0200, Anisse Astier wrote: > On Thu, Jun 13, 2019 at 06:14:44PM +0100, Dave Martin wrote: > > On Thu, Jun 13, 2019 at 06:38:01PM +0200, Anisse Astier wrote: > > > -#define SVE_PT_VL_INHERIT (PR_SVE_VL_INHERIT >> 16) > > > -#define SVE_PT_VL_ONEXEC (PR_SVE_SET_VL_ONEXEC >> 16) > > > +#define SVE_PT_VL_INHERIT (1 << 1) /* PR_SVE_VL_INHERIT */ > > > +#define SVE_PT_VL_ONEXEC (1 << 2) /* PR_SVE_SET_VL_ONEXEC */ > > > > Makes sense, but... > > > > Since sve_context.h was already introduced to solve a closely related > > problem, I wonder whether we can provide shadow definitions there, > > similarly to way the arm64/include/uapi/asm/ptrace.h definitions are > > derived. Although it's a slight abuse of that header, I think that > > would be my preferred approach. > > Yes I saw this, and I considered doing something similar. But, those > defines are in uapi/linux/prctl.h, which does not include any asm/*.h > header. This would have then required adding a full infrastructure for > asm/prctl.h (that could then include sve_context.h for example), which > does not exist yet, instead of copying these two values.
x86 appears to have an asm/prctl.h implementation, but it's not included by anybody so I guess that doesn't really help us here. > Since this is part of the kernel-userspace ABI, I don't see this values > changing anytime soon, which is why I thought copying them shouldn't be > a big issue. Certainly not a big issue, just that the harder we make this to change the better. > A simple solution would be to to include sve_context.h or a third > header, maybe linux/prctl_arm64_sve.h (with only these two/five > defines), in linux/prctl.h, and reuse it in uapi/asm/ptrace.h; but this > would break the self-contained nature of linux/prctl.h. > > > > Otherwise, at least make the required relationship between ptrace.h and > > prctl.h constants a bit more obvious, say, > > > > #define SVE_PT_VL_INHERIT ((1 << 17) /* PR_SVE_SET_VL_INHERIT */ >> 16) > > This one is much simpler and closer to what I had in mind with this > patch. > > Will, what do you think of this second approach Dave proposed ? Duplication is grotty, but it does the job so I'm ok with it. I don't have any better ideas. Thanks, Will
