Re: [Xen-devel] [PATCH 2/2] Xen/x86: Improve information from domain_crash_synchronous

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.09.13 at 20:18, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> As it currently stands, the string "domain_crash_sync called from entry.S" is
> not helpful at identifying why the domain was crashed, and a debug build of
> Xen doesn't help the matter
> 
> This patch improves the information printed, by pointing to where the crash
> decision was made.

Looks quite useful.

> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -263,6 +263,7 @@ ENTRY(compat_int80_direct_trap)
>  /*   {[ERRCODE,] EIP, CS, EFLAGS, [ESP, SS]}                             */
>  /* %rdx: trap_bounce, %rbx: struct vcpu                                  */
>  /* On return only %rbx and %rdx are guaranteed non-clobbered.            */
> +.globl compat_create_bounce_frame
>  compat_create_bounce_frame:

Is the addition above a left-over? I don't see any use of the
label outside of this file.

> @@ -329,7 +330,12 @@ UNLIKELY_END(compat_bounce_failsafe)
>          movzwl TRAPBOUNCE_cs(%rdx),%eax
>          /* Null selectors (0-3) are not allowed. */
>          testl $~3,%eax
> -        jz    domain_crash_synchronous
> +.Lcompat_bounce_null_selector:
> +UNLIKELY_START(z, compat_bounce_null_selector)
> +        lea   .Lcompat_bounce_null_selector(%rip), %rdi
> +        jmp   asm_domain_crash_synchronous
> +        ud2a
> +UNLIKELY_END(compat_bounce_null_selector)

Here and further down you don't really need the label at the
start of the unlikely section - the place can as well be identified
by using

        lea   (%rip), %rdi

inside that section (the place is still unique, just outside the
original code stream, i.e. just slightly more difficult to
re-associate).

Jan


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