A couple of minor nits below. On Wed, Jun 12, 2019 at 03:21:11PM +0100, Vincenzo Frascino wrote: > --- a/Documentation/arm64/tagged-pointers.txt > +++ b/Documentation/arm64/tagged-pointers.txt > @@ -18,7 +18,8 @@ Passing tagged addresses to the kernel > -------------------------------------- > > All interpretation of userspace memory addresses by the kernel assumes > -an address tag of 0x00. > +an address tag of 0x00, unless the userspace opts-in the ARM64 Tagged > +Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl(). > > This includes, but is not limited to, addresses found in: > > @@ -31,18 +32,23 @@ This includes, but is not limited to, addresses found in: > - the frame pointer (x29) and frame records, e.g. when interpreting > them to generate a backtrace or call graph. > > -Using non-zero address tags in any of these locations may result in an > -error code being returned, a (fatal) signal being raised, or other modes > -of failure. > +Using non-zero address tags in any of these locations when the > +userspace application did not opt-in to the ARM64 Tagged Address ABI, Nitpick: drop the comma after "ABI," since a predicate follows. > +may result in an error code being returned, a (fatal) signal being raised, > +or other modes of failure. > > -For these reasons, passing non-zero address tags to the kernel via > -system calls is forbidden, and using a non-zero address tag for sp is > -strongly discouraged. > +For these reasons, when the userspace application did not opt-in, passing > +non-zero address tags to the kernel via system calls is forbidden, and using > +a non-zero address tag for sp is strongly discouraged. > > Programs maintaining a frame pointer and frame records that use non-zero > address tags may suffer impaired or inaccurate debug and profiling > visibility. > > +A definition of the meaning of ARM64 Tagged Address ABI and of the > +guarantees that the ABI provides when the userspace opts-in via prctl() > +can be found in: Documentation/arm64/tagged-address-abi.txt. > + > > Preserving tags > --------------- > @@ -57,6 +63,9 @@ be preserved. > The architecture prevents the use of a tagged PC, so the upper byte will > be set to a sign-extension of bit 55 on exception return. > > +This behaviours are preserved even when the the userspace opts-in the ARM64 "These" ... "opts in to" > +Tagged Address ABI via the PR_SET_TAGGED_ADDR_CTRL prctl(). > + > > Other considerations > -------------------- > -- > 2.21.0 -- Catalin
