Re: [PATCH RFC 1/4] Generic BUG handling.

From: Andrew Morton
Date: Thu Sep 28 2006 - 19:34:06 EST

On Thu, 28 Sep 2006 15:54:45 -0700
Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> This patch adds common handling for kernel BUGs, for use by
> architectures as they wish. The code is derived from arch/powerpc.
> The advantages of having common BUG handling are:
> - consistent BUG reporting across architectures
> - shared implementation of out-of-line file/line data
> This means that in inline impact of BUG is just the illegal
> instruction itself, which is an improvement for i386 and x86-64.
> A BUG is represented in the instruction stream as an illegal
> instruction, which has file/line/function information associated with
> it. This extra information is stored in the __bug_table section in
> the ELF file.
> When the kernel gets an illegal instruction, it first confirms it
> might possibly be from a BUG (ie, in kernel mode, the right illegal
> instruction). It then calls report_bug(). This searches __bug_table
> for a matching instruction pointer, and if found, prints the
> corresponding file/line/function information.
> Some architectures (powerpc) implement WARN using the same mechanism;
> if the illegal instruction was the result of a WARN, then report_bug()
> returns 1; otherwise it returns 0.


> lib/bug.c keeps a list of loaded modules which can be searched for
> __bug_table entries. The architecture must call
> module_bug_finalize()/module_bug_cleanup() from its corresponding
> module_finalize/cleanup functions.

What is the locking for these lists? I don't see much in here. It has
implications for code which wants to do BUG while holding that lock..

> This patch also converts i386, x86-64 and powerpc to use this
> infrastructure. I have only tested i386; x86-64 and powerpc are not
> even compile-tested in this patch.
> Because powerpc also records the function name, I added this to i386
> and x86-64 for consistency. Strictly speaking the function name is
> redundant with kallsyms, so perhaps it can be dropped from powerpc.

I agree that the function name is a rather gratuitous space-consumer.

> + /* Support for BUG */
> + struct list_head bug_list;
> + struct bug_entry *bug_table;
> + unsigned num_bugs;

Shouldn't this be u64? ;)

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