[PATCH] ntdll/tests: Do not write to fs, gs when testing cleared segment regs on x64.

[Zebediah Figura (she/her)]

On 6/23/21 6:57 AM, Paul Gofman wrote:
> Fixes the crash in test.
> 
> Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=51152
> Signed-off-by: Paul Gofman <pgofman at codeweavers.com>
> ---
>   dlls/ntdll/tests/exception.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
> 
> diff --git a/dlls/ntdll/tests/exception.c b/dlls/ntdll/tests/exception.c
> index 328882c1a23..7b83c06a8db 100644
> --- a/dlls/ntdll/tests/exception.c
> +++ b/dlls/ntdll/tests/exception.c
> @@ -2908,13 +2908,27 @@ static const struct exception
>           0x31, 0xc0, /* xor %eax,%eax */
>           0x8e, 0xc0, /* mov %eax,%es */
>           0x8e, 0xd8, /* mov %eax,%ds */
> +#if 0
> +        /* TODO_WINE: fs/gs base is reset on Linux when setting the
> +           segment value and this is not currently handled.
> +           Disable this part to avoid crashing the test. */
>           0x8e, 0xe0, /* mov %eax,%fs */
>           0x8e, 0xe8, /* mov %eax,%gs */
> +#else
> +        0x90, 0x90, /* nop */
> +        0x90, 0x90, /* nop */
> +#endif
>           0xfa,       /* cli */
>           0x58,       /* pop %rax */
> +#if 0
>           0x8e, 0xe8, /* mov %eax,%gs */
>           0x58,       /* pop %rax */
>           0x8e, 0xe0, /* mov %eax,%fs */
> +#else
> +        0x58,       /* pop %rax */
> +        0x90, 0x90, /* nop */
> +        0x90, 0x90, /* nop */
> +#endif
>           0x58,       /* pop %rax */
>           0x8e, 0xd8, /* mov %eax,%ds */
>           0x58,       /* pop %rax */
> 

I don't object to disabling these tests, but I don't think the comment 
is accurate. We've been able to observe fsbase being reset to zero on 
one AMD processor, with Linux 5.12, but not another; the behaviour 
violates the AMD specification, and it's not clear that the kernel is 
actually getting involved.