[PATCH v6 2/5] x86: Add SFrame support for x86 architecture

[Florian Weimer]

* Adhemerval Zanella Netto:

>> +  if (*(unsigned char *)(pc+0) == 0x48
>> +      && *(unsigned long long *)(pc+1) == RT_SIGRETURN_SYSCALL)
>
> This is strictly UB, although x86_64 supports unaligned access.  You can 
> use something like:
>
> #define __read_unaligned_t(__type, __ptr) ({                            \
>         const struct { type x; } __attribute__((__packed__)) * __pptr = \
>           (typeof(_pptr))(__ptr);                                       \
>         __pptr->x;                                                      \
> })
> #define read_unaligned(ptr)   __read_unaligned_t(typeof(*(ptr)), (ptr))
>
> Or the memcpy to a temporary (as we do on some code internally).  Afaik 
> the packet attribute tend to generate better code.

I would just use memcmp.  GCC will expand it inline if the ordering is
not used.

Thanks,
Florian