Re: [RFC PATCH v2 2/2] selftests/x86: sysret_rip: Add more syscall tests with respect to `%rcx` and `%r11`

H. Peter Anvin
2023-01-24T06:18:55Z

On 1/23/23 18:27, Ammar Faizi wrote:
> From: Ammar Faizi <ammarfaizi2@gnuweeb.org>
>
> Test that:
>
> - "syscall" in a FRED system doesn't clobber %rcx and %r11.
> - "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags.
>
> Test them out with a trivial system call like __NR_getppid and friends
> which are extremely likely to return with SYSRET on an IDT system; check
> that it returns a nonnegative value and then save the result.
>

"Nonnegative" here should be "valid"; it is an implementation detail
that the error value is -1.

However, you are not checking that you don't get a mix of REGS_SAVED and
REGS_SYSRET, which is a major part of the point.

-hpa