Re: [Qemu-devel] qemu-x86_64 on i386 host: SIGSEGV

[Michael Tokarev <mjt@tls.msk.ru>]

24.03.2013 14:59, Peter Maydell wrote:
> On 24 March 2013 10:43, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> $ ./x86_64-linux-user/qemu-x86_64 bash64
>> qemu: uncaught target signal 11 (Segmentation fault) - core dumped
>> Segmentation Fault
> 
> Are 64 bit linux-user guests on 32 bit hosts supposed to work?
> I would expect them to be at best pretty unreliable.

What's the reason we build these binaries in that case?

What about qemu-x86_64 on other 32bit arches (arm)?  Is
there a list of combinations (host/target) which are
supposed to work and which don't, somewhere?

>> $ gdb x86_64-linux-user/qemu-x86_64
>> (gdb) ru bash64
>> Program received signal SIGSEGV, Segmentation fault.
>> disas_insn (s=s@entry=0xffffcf98, pc_start=18446744073699066880)
>>     at target-i386/translate.c:4107
>> 4107        b = ldub_code(s->pc);
>> (gdb) p *s
>> $1 = {override = -1, prefix = 1484501952, aflag = 1, dflag = 1484503884,
>>   pc = 18446744073699066880, is_jmp = 0, cs_base = 0, pe = 1, code32 = 1,
> 
> PC is FFFFFFFFFF600400 so either we've messed it up already or this
> is just "64 bit address space doesn't fit in a 32 bit one".

>> Some binaries works - for example, gzip (it prints "qemu: Unsupported syscall:
>> 202" on the way which is a different issue).
> 
> Yes. That is just the usual "x86 linux-user isn't really supported":
> 202 is TARGET_NR_futex, which works on other target archs but
> won't on x86 until somebody actually fixes support for threaded
> guests in x86 to at least the level it is for other targets.

Maybe we should stop building x86 linux-user completely?

Thanks,

/mjt