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    Subject[PATCH] a more efficient BUG() macro
    I was poking around in a vmlinux the other day and was surprised at the 
    amount of repetitive crap text that was in there. For example, try:

    strings vmlinux|grep $PWD|wc -c

    which gets some 70KB in my case - depends on strlen($PWD) obviously. The
    culprit is BUG() in a static inline that is in a header file. In this
    case cpp expands __FILE__ to the full path of the header file in question.
    (IIRC there is a __BASEFILE__ that would be a better choice than __FILE__)

    There is also some 5 to 10k worth of "kernel BUG at %s:%d!\n" scattered
    through a typical vmlinux. Note that neither of these show up in [b]zImage
    size since they compress to something like 99%, but they do cost memory once
    the kernel is booted.

    Anyway this small patch makes sure there is only one "kernel BUG..." string,
    and dumps __FILE__ in favour of an address value since data is
    needed to make full use of the BUG() dump anyways. The memory stats of two
    otherwise identical kernels:

    Memory: 22004k/24576k available (1163k kernel code, 2184k reserved,
    309k data, 64k init, 0k highmem)
    Memory: 22076k/24576k available (1163k kernel code, 2112k reserved,
    238k data, 64k init, 0k highmem)

    so the lightweight BUG() nets a worthwhile (IMHO) saving of 72KB for this
    particular kernel. (Which is even more than the __init goodies recover.)
    Patch is against 2.4.2pre3 and is fully contained within i386 files.
    I can supply a 2.2.x version of the patch if there is demand for it.


    diff -ur linux~/arch/i386/kernel/i386_ksyms.c linux/arch/i386/kernel/i386_ksyms.c
    --- linux-g/arch/i386/kernel/i386_ksyms.c Thu Jan 11 09:06:12 2001
    +++ linux-g-bug/arch/i386/kernel/i386_ksyms.c Thu Feb 15 03:50:18 2001
    @@ -78,6 +78,7 @@
    /* Networking helper routines. */
    /* Delay loops */
    diff -ur linux~/arch/i386/kernel/setup.c linux/arch/i386/kernel/setup.c
    --- linux-g/arch/i386/kernel/setup.c Wed Feb 14 02:39:58 2001
    +++ linux-g-bug/arch/i386/kernel/setup.c Thu Feb 15 04:13:31 2001
    @@ -105,6 +105,8 @@
    char ignore_irq13; /* set if exception 16 works */
    struct cpuinfo_x86 boot_cpu_data = { 0, 0, 0, 0, -1, 1, 0, 0, -1 };

    +const char *bugstring="<1>kernel BUG at 0x%p\n";
    unsigned long mmu_cr4_features;

    diff -ur linux~/include/asm-i386/page.h linux/include/asm-i386/page.h
    --- linux-g/include/asm-i386/page.h Sat Dec 16 04:02:20 2000
    +++ linux-g-bug/include/asm-i386/page.h Thu Feb 15 04:25:29 2001
    @@ -86,10 +86,13 @@
    * Tell the user there is some problem. Beep too, so we can
    * see^H^H^Hhear bugs in early bootup as well!
    -#define BUG() do { \
    - printk("kernel BUG at %s:%d!\n", __FILE__, __LINE__); \
    +extern const char *bugstring; /* in i386/kernel/setup.c - Paul G. */
    +#define BUG() ({ \
    + __label__ bugaddr; \
    +bugaddr: \
    + printk(bugstring, &&bugaddr); \
    __asm__ __volatile__(".byte 0x0f,0x0b"); \
    -} while (0)

    #define PAGE_BUG(page) do { \
    BUG(); \

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