Re: [RFC PATCH] kernel/kallsyms.c: only show legal kernel symbol

From: Ming Lei
Date: Thu Oct 24 2013 - 01:42:21 EST

On Thu, Oct 24, 2013 at 9:21 AM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> Ming Lei <tom.leiming@xxxxxxxxx> writes:
>> Address of non-module kernel symbol should always be located
>> from CONFIG_PAGE_OFFSET on, so only show these legal kernel
>> symbols in /proc/kallsyms.
>> On ARM, some symbols(see below) may drop in relocatable code, so
>> perf can't parse kernel symbols any more from /proc/kallsyms, this
>> patch fixes the problem.
>> 00000000 t __vectors_start
>> 00000020 A cpu_v7_suspend_size
>> 00001000 t __stubs_start
>> 00001004 t vector_rst
>> 00001020 t vector_irq
>> 000010a0 t vector_dabt
>> 00001120 t vector_pabt
>> 000011a0 t vector_und
>> 00001220 t vector_addrexcptn
>> 00001224 t vector_fiq
>> 00001224 T vector_fiq_offset
>> The issue can be fixed in scripts/kallsyms.c too, but looks this
>> approach is easier.
> This fix looks hacky; if these symbols are not available, don't just
> remove them from /proc/kallsyms, but don't put them in the kernel at
> all.
> That way, they won't interfere with other kallsyms uses (eg. backtrace).

Yes, I agree.

> Or, better, figure out a smart way of excluding them by knowing why
> these symbol addresses are wrong.

Actually the problem is caused by commit b9b32bf70f2(ARM: use linker
magic for vectors and vector stubs), maybe Russell can figure out a smart
way to exclude these symbols.

Ming Lei
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