Re: [PATCH 1/23] Make register values available to panic notifiers

From: David Howells
Date: Mon Apr 12 2010 - 08:46:33 EST


Russell King <rmk@xxxxxxxxxxxxxxxx> wrote:

> Can you explain why you want this?
>
> I'm wondering about the value of saving the registers; normally when a panic
> occurs, it's because of a well defined reason, and not because something
> went wrong in some CPU register; to put it another way, a panic() is a
> more controlled exception than a BUG() or a bad pointer dereference.

+1.

I found in FS-Cache and CacheFiles that often the things I most wanted to know
when I had something of the form:

if (A == B)
BUG();

was a and b, so I made the following macro:

#define ASSERTCMP(X, OP, Y) \
do { \
if (unlikely(!((X) OP (Y)))) { \
printk(KERN_ERR "\n"); \
printk(KERN_ERR "AFS: Assertion failed\n"); \
printk(KERN_ERR "%lu " #OP " %lu is false\n", \
(unsigned long)(X), (unsigned long)(Y)); \
printk(KERN_ERR "0x%lx " #OP " 0x%lx is false\n", \
(unsigned long)(X), (unsigned long)(Y)); \
BUG(); \
} \
} while(0)

which I could then call like this:

ASSERTCMP(A, ==, B);

and if the assertion failed, it prints A and B explicitly. This is much
easier than trying to pick the values out of a register dump, especially as
the compiler may be free to clobber A or B immediately after testing them.

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/