Re: [Xen-devel] [PATCH ARM v3 7/7] mini-os: initial ARM support

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>]

Ian Campbell, le Thu 12 Jun 2014 08:41:54 +0100, a écrit :
> On Wed, 2014-06-11 at 21:24 +0200, Samuel Thibault wrote:
> > > +static inline unsigned long __xchg(unsigned long x, volatile void * ptr, 
> > > int size)
> > > +{
> > > +    //TODO
> > > +    unsigned volatile long y, tmp = 0;
> > > +    switch(size){
> > > +    case 1:
> > > +#if CPU_EXCLUSIVE_LDST
> > > +        __asm__ __volatile__("1:ldrexb %0, [%1]\n"
> > > +            "strexb %3, %2, [%1]\n"
> > > +            "cmp %3, #1\n"
> > > +            "beq 1b\n\n"
> > > +            "dmb\n":"=&r"(y):"r"(ptr), "r"(x), "r"(tmp):"memory");
> > > +#else
> > > +        y = (*(char *)ptr) & 0x000000ff;
> > > +        *((char *)ptr) = (char)x;
> > 
> > The second version is very fragile :) I'd rather put a strong #warning
> > here, to make sure nobody ever uses that code for anything close to
> > production level.
> 
> ldrexb is guaranteed to be available on any platform which can run Xen.
> For one thing xen uses them (unconditionally) itself.

I'd rather see minios us them unconditionally then, to avoid the risk of
running unsafe code :)

Samuel

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