Re: [PATCH] more helpful WARN_ON and BUG_ON messages

[Jeremy Fitzhardinge <jeremy@goop.org>]

Eric Sandeen wrote:
> After a few bugs I encountered in FC6 in buffer.c, with output like:
>
> Kernel BUG at fs/buffer.c: 2791
>
> where buffer.c contains:
>
> ...
>         BUG_ON(!buffer_locked(bh));
>         BUG_ON(!buffer_mapped(bh));
>         BUG_ON(!bh->b_end_io);
> ...
>
> around line 2790, it's awfully tedious to go get the exact failing kernel tree
> just to see -which- BUG_ON was encountered.
>
> Printing out the failing condition as a string would make this more helpful IMHO.
>   

This seems like a generally useful idea - certainly more valuable than 
storing+printing the function name.

You might want to look at the BUG patches I wrote, which are currently 
in -mm.  I added general machinery to allow architectures to easily 
implement BUG() efficiently (ie, with a minimal amount of BUG-related 
icache pollution).  If you were to store the BUG_ON expression, it would 
be best to extend struct bug_entry and store it there - doing it in 
asm-generic BUG_ON() means you still end up with code to set up the 
printk in the mainline code path, and it also won't honour 
CONFIG_DEBUG_BUGVERBOSE being disabled.

    J