* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > +static inline void __noreturn BUG(void)
> > +{
> > + __asm__ __volatile__("break %0" : : "i" (BRK_BUG));
> > + /* Fool GCC into thinking the function doesn't return. */
> > + while (1)
> > + ;
> > +}
>
> This kind of sucks, doesn't it? It adds instructions into the
> kernel text, very frequently on fast paths. Those instructions are
> never executed, and we're blowing away i-cache just to quash
> compiler warnings.
>
> For example, this:
>
> --- a/arch/x86/include/asm/bug.h~a
> +++ a/arch/x86/include/asm/bug.h
> @@ -22,14 +22,12 @@ do { \
> ".popsection" \
> : : "i" (__FILE__), "i" (__LINE__), \
> "i" (sizeof(struct bug_entry))); \
> - for (;;) ; \
> } while (0)
>
> #else
> #define BUG() \
> do { \
> asm volatile("ud2"); \
> - for (;;) ; \
> } while (0)
> #endif
>
> _
>
> reduces the size of i386 mm/vmalloc.o text by 56 bytes.
yes - the total image effect is significantly - recently looked at how
much larger !CONFIG_BUG builds would get if we inserted an infinite
loop into them - it was in the 50K text range (!).
but in the x86 ud2 case we could guarantee that we wont ever return
from that exception. Mind sending a patch with a signoff, a
description and an infinite loop in the u2d handler?
Ingo
