On Thu, 28 Sep 2006, Andi Kleen wrote:
> On Thu, Sep 28, 2006 at 03:30:12AM -0700, Jeremy Fitzhardinge wrote:
> > Andi Kleen wrote:
> > >But no out of line section. So overall it's smaller, although the cache
> > >footprint
> > >is 2 bytes larger. But then is 2 bytes larger really an issue? We don't
> > >have
> > >_that_ many BUGs anyways.
> > >
> >
> > I think the out of line section is a feature; no point in crufting up
> > the icache with BUG gunk, especially since a number of them are on
> > fairly hot paths.
>
> It's 10 bytes per BUG.
Or 9 bytes per BUG: I protested about the disassembly problem back
when the minimized BUG() first went in, and have been using "ljmp"
in my i386 builds ever since:
--- 2.6.18-git9/arch/i386/kernel/traps.c 2006-09-28 12:03:47.000000000 +0100
+++ linux/arch/i386/kernel/traps.c 2006-09-28 16:23:56.000000000 +0100
@@ -422,10 +422,10 @@ static void handle_BUG(struct pt_regs *r
char *file;
char c;
- if (probe_kernel_address((unsigned short __user *)(eip + 2),
+ if (probe_kernel_address((unsigned short __user *)(eip + 7),
line))
break;
- if (__get_user(file, (char * __user *)(eip + 4)) ||
+ if (__get_user(file, (char * __user *)(eip + 3)) ||
(unsigned long)file < PAGE_OFFSET || __get_user(c, file))
file = "<bad filename>";
--- 2.6.18-git9/include/asm-i386/bug.h 2006-09-20 04:42:06.000000000 +0100
+++ linux/include/asm-i386/bug.h 2006-09-28 16:23:56.000000000 +0100
@@ -13,9 +13,11 @@
#ifdef CONFIG_DEBUG_BUGVERBOSE
#define BUG() \
__asm__ __volatile__( "ud2\n" \
- "\t.word %c0\n" \
- "\t.long %c1\n" \
- : : "i" (__LINE__), "i" (__FILE__))
+ "\t.byte 0xea\n" \
+ "\t.long %c0\n" \
+ "\t.word %c1\n" \
+ : : "i" (__FILE__), "i" (__LINE__))
+ /* "ljmp long short" so disassemblers can make sense of it */
#else
#define BUG() __asm__ __volatile__("ud2\n")
#endif
-
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