linux-kernel - Re: [PATCH v5 5/8] kbuild: add fine grained build dependencies for exported symbols

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Date:	Fri, 4 Mar 2016 23:53:53 +0100
From:	Michal Marek <mmarek@...e.cz>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/8] kbuild: add fine grained build dependencies for
 exported symbols

Dne 4.3.2016 v 23:51 Michal Marek napsal(a):
> Dne 4.3.2016 v 06:40 Nicolas Pitre napsal(a):
>> +cmd_and_fixdep =                                                             \
>> +	$(echo-cmd) $(cmd_$(1));                                             \
>> +	$(ksym_dep_filter) |                                                 \
>> +		scripts/basic/fixdep -e $(depfile) $@ '$(make-cmd)'          \
>> +			> $(dot-target).tmp;	                             \
>> +	rm -f $(depfile);                                                    \
>> +	mv -f $(dot-target).tmp $(dot-target).cmd;
> 
> While trying this, I got a SIGBUS from fixdep once. My theory is that
> the depfile is mmap()ed by fixdep and modified by the preprocesor run at
> the same time. I could not reproduce this so far (still trying). But if
> it's really this race, the fix would be to disable dependency generation
> in the preprocessor by passing -Wp,MD,/dev/null or somesuch. But we
> never had this problem with genksyms, which is weird. It could as well
> be that my build machine's memory is faulty :(.

Actually, genksyms does not ran in parallel. neither before nor after
this patch.

Michal