On Tue, Sep 29, 2026 at 05:27:28PM +0100, Mark Rutland wrote: > On Tue, Sep 01, 2026 at 06:06:43PM +0100, Mark Brown wrote: > > When they detect corruption the fp-stress test loads print load specific > > diagnostics and exits with a failure status. In preparation for > > building versions intended to run as KVM guests factor the exits into > > asm-utils-linux.S. > > > > No functional change. > > This is a good cleanup, but I do think it'd be worth noting that some of > the existing asm was wrong and worked by coincidence. > > I did mention that in the patches I linked you to a while back: > > > https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?id=922d15ef46cb486a79f168949e103f6df26f4fba
Sorry, that was the wrong link; I meant to share: https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?id=2db277185f5c252decdf49b25cd461782e890cd1 ... which was another patch from that cleanup series: https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/selftests/cleanup The description of the problem from the commit message was: | The barf functions in the fp-stress sub-tests erroneously place the | status value into x1 (rather than x0) when invoking the exit syscall, | potentially returning a different status than expected. | | By coincidence, the low 8 bits of x0 happen to be non-zero for all of | these cases, and the exit will be treated as a failure by the fp-stress | harness, which is the desired behaviour. Hence this doesn't lead to | failing tests being reported as passing. | | In all cases x0 contains either: | | * The result of the prior write syscall made by the puts macro, which is | a write of the two character string "]\n". | | * The result of the prior write syscall made by the putdecn() function, | which is a write of the single-character '\n'. | | In either case, the return value of that write syscall may be a non-zero | number of bytes written, or a negative error code. As the relevant | strings are fewer than 256 characters, and all (positive) error codes | are less than 256, the value in the low 8 bits of x0 will not be zero. Mark.
