Re: [XenPPC] [PATCH] Print backtrace on BUG

[Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>]

Bah, it's too early for GCC asm:

> > +    asm("mr %0, 1" :  
> > "=r" (sp));                                          \
> > +    asm("mflr %0" :  
> > "=r" (lr));                                           \
> > +    asm("mflr %0; bl 1f; 1: mflr %1; mtlr %0" : "=r" (tp),  
> > "=r" (pc));    \
>         asm("bl $+4 ; mflr %0; mtlr %1" : "=r"(pc) : "r"(lr));            \
>
> > +    show_backtrace(sp, lr,  
> > pc);                                           \
> > +    __asm__ __volatile__  
> > ( "trap" );                                      \
> > +} while ( 0 )
> ...and the one "asm" where you put "volatile" on is the only one that
> doesn't need it :-)  (and no __ is needed either).
>
> Alternatively (and preferred), you can make a single statement out
> of the first three asm statements.
In fact, you _have_ to make those three into one; even "volatile asm"s
can be reordered by the compiler, if there's no data dependency.

The "trap" asm is always volatile (it has no parameters); it can still
be reordered though.  You can use __builtin_trap() here instead.


Segher


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