Messages in this thread | | | Date | Fri, 21 Nov 2008 15:48:42 -0800 | From | David Daney <> | Subject | Re: [PATCH] MIPS: Make BUG() __noreturn. |
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Andrew Morton wrote: > > > Yup, this change will fix some compile warnings which will never be > fixed in any other way for mips. > >> +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. > > I wonder if there is any clever way in which we can do this without > introducing additional runtime cost.
As I said in the other part of the thread, We are working on a GCC patch that adds a new built-in function '__builtin_noreturn()', that you could substitute for 'for(;;);' that emits no instructions in this case.
David Daney
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