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    SubjectRe: [PATCH] MIPS: Make BUG() __noreturn.
    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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