Re: CVS commit: src/tests/lib/libc/gen (address alignment)

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On 21.04.12 19:38, Jean-Yves Migeon wrote:
> Le 21/04/12 16:31, Jean-Yves Migeon a écrit :
>>> Okay, thanks for the report. So this rules out Virtual Box, it seems to
>>> happen on native amd64 too.
>>>
>>> I am taking a look right now.
>>
>> This seems to be a bug in the trap handling code. The signal is caught
>> correctly (it reaches T_ALIGNFLT|T_USER in trap()), but things blow up
>> just after: we end signalling the process with a SIGILL (which does not
>> come from trap()).
>>
>> Using 32 bits compat mode (cc -m 32) also causes the crash. So something
>> in e_trapsignal() or userret() goes wrong. Still digging.
> 
> Interesting. The "uncatchable" SIGILL comes from sendsig_siginfo [1] and
> is used in a way that the signal will force-exit the program (when the
> copyout fails). It's a "feature" I was not aware of.
> 
> Anyway, upon entering trap() for this exception (trap11), it looks like
> the trapframe is a mess:
> 
> pid 470 (malign): BUS/SEGV (107) at rip 0 addr 7f7ff7701020
> rip 0x0 rsp 0x50202 rfl 0x1f
> rdi 0x7f7ff7701080 rsi 0x8 rdx 0xf7701078
> rcx 0x0 r8 0x7 r9 0x7f7ff770178
> [...]
> 
> rip 0x0 and rsp 0x50202 look really abnormal to me. I'll have a look in
> FreeBSD, that's probably a group of exceptions that have to be handled
> differently.

rip 0x0 often means that a function pointer has been called which is NULL.

Christoph