Re: [Xen-devel] [PATCH] x86emul: correct stub invocation constraints

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.04.17 at 16:01, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 04/25/2017 05:04 AM, Jan Beulich wrote:
>> Stub invocations need to have the space the stub occupies as an input,
>> to prevent the compiler from re-ordering (or omitting) writes to it.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>> @@ -837,7 +837,8 @@ do{ asm volatile (
>>                     ".popsection\n\t"                                    \
>>                     _ASM_EXTABLE(.Lret%=, .Lfix%=)                       \
>>                     : [exn] "+g" (res_), constraints,                    \
>> -                     [stub] "rm" (stub.func) );                         \
>> +                     [stub] "rm" (stub.func),                           \
>> +                     "m" (*(uint8_t(*)[MAX_INST_LEN + 1])stub.ptr) );   \
>>      if ( unlikely(~res_.raw) )                                          \
>>      {                                                                   \
>>          gprintk(XENLOG_WARNING,                                         \
>> @@ -853,7 +854,8 @@ do{ asm volatile (
>>  #else
>>  # define invoke_stub(pre, post, constraints...)                         \
>>      asm volatile ( pre "\n\tcall *%[stub]\n\t" post                     \
>> -                   : constraints, [stub] "rm" (stub.func) )
>> +                   : constraints, [stub] "rm" (stub.func),              \
>> +                     "m" (*(uint8_t(*)[MAX_INST_LEN + 1])stub.buf) )
>>  #endif
>>  
>>  #define emulate_stub(dst, src...) do {                                  \
>>
> 
> 
> This breaks on old compilers:
> 
> FC-64
> <build@build-mk2:~/xtt-x86_64/bootstrap/xen.git/tools/fuzz/x86_instruction_em
> ulator>
> gcc --version
> gcc (GCC) 4.4.4 20100503 (Red Hat 4.4.4-2)

Btw., I've just realized that I did use an old gcc only on the
hypervisor build. Do you see the same issue there, or is this tools
side specific?

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel