Re: [Qemu-devel] [PATCH] cpu-exec(): also reload CPUClass *cc after longjmp return

[Stefan Weil]

Am 05.10.2013 19:54, schrieb Juergen Lock:
> On Fri, Oct 04, 2013 at 09:15:37AM +0200, Jan Kiszka wrote:
>> On 2013-10-03 18:05, Peter Maydell wrote:
>>> On 3 October 2013 23:09, Juergen Lock <address@hidden> wrote:
>>>> Local variable CPUClass *cc needs to be reloaded after return from longjmp
>>>> too.  (This fixes the mips-softmmu crash observed on FreeBSD when qemu is
>>>> built with clang.)
>>>>
>>>> Signed-off-by: Juergen Lock <address@hidden>
>>>> Found-by: Dimitry Andric <address@hidden>
>>>>
>>>> --- a/cpu-exec.c
>>>> +++ b/cpu-exec.c
>>>> @@ -681,6 +681,10 @@ int cpu_exec(CPUArchState *env)
>>>>               * local variables as longjmp is marked 'noreturn'. */
>>>>              cpu = current_cpu;
>>>>              env = cpu->env_ptr;
>>>> +#if !(defined(CONFIG_USER_ONLY) && \
>>>> +      (defined(TARGET_M68K) || defined(TARGET_PPC) || 
>>>> defined(TARGET_S390X)))
>>>> +            cc = CPU_GET_CLASS(cpu);
>>>> +#endif
>>> This is a c compiler or libc bug -- the C standard says that this
>>> local variable should not be trashed by the longjmp. We were
>>> actually discussing removing the current workarounds there...
>> But we didn't decide if we should stop supporting the affected compiler
>> versions.
>>
>> Does this issue also exist with the latest clang version available for
>> your platform?
>>
> It happens with up to date clang as it's in FreeBSD 10.0-current
> which is due for a release soon.  I think the clang folks are looking
> into this issue but I don't know if a fix will make it into the
> release...  (For now I've added the workaround to the FreeBSD
> qemu-devel port.)
>
>  Thanx,
>       Juergen


Could you try whether QEMU crashes when it was configured with
TCG interpreter (--enable-tcg-interpreter)? If it does not crash, it
might be that TCG does not save / restore enough registers.

Which register is used for the local variable 'cc'?

Regards,
Stefan