[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] Xen/x86: Improve information from domain_crash_synchronous
>>> On 05.09.13 at 11:44, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote: > On 05/09/13 09:15, Jan Beulich wrote: >>>>> 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. > > This is for the benifit of print_symbol(), which will now give > create_bounce_frame()+some rather than trap_nop()+loads. That shouldn't be happening - whether a symbol is local or global should not matter to symbol table generation and consumption. The matter would be different is the label started with .L... >>> @@ -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). > > But in an unlikely section, %rip is shifted quite a lot from %rip of the > code immediately before. This is also for the benefit of print_symbol() > which will pick up the {compat_,}create_bounce_frame rather than the > global symbol surrounding the unlikely section. I understand that, but stray labels are at clear risk of getting deleted by a subsequent cleanup patch anyway. Hence either we need a solution without stray labels, or live with the need to re-associate the address pointed to be the crash log messages to the original function. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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