linux-kernel - Re: [PATCH] genksyms: Duplicate function pointer type definitions segfault

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Message-ID: <55D5CE04.2050705@suse.cz>
Date:	Thu, 20 Aug 2015 14:54:28 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Richard Yao <ryao@...too.org>, linux-kernel@...r.kernel.org
Cc:	Richard Yao <richard.yao@...sterhq.com>,
	Madhuri Yechuri <madhuriyechuri@...sterhq.com>
Subject: Re: [PATCH] genksyms: Duplicate function pointer type definitions
 segfault

On 2015-07-21 01:52, Richard Yao wrote:
> From: Richard Yao <richard.yao@...sterhq.com>
> 
> I noticed that genksyms will segfault when it sees duplicate function
> pointer type declaration when I placed the same function pointer
> definition in two separate headers in a local branch as an intermediate
> step of some refactoring. This can be reproduced by piping the following
> minimal test case into `genksyms -r /dev/null` or alternatively, putting
> it into a C file attempting a build:
> 
> int (*f)();
> int (*f)();
> 
> Attaching gdb to genksyms to understand this failure is useless without
> changing CFLAGS to emit debuginfo. Once you have debuginfo, you will
> find that the failure is that `char *s` was NULL and the program
> executed `while(*s)`. At which point, further debugging requires
> familiarity with compiler front end / parser development.
> 
> What happens is that flex identifies the first instance of the token "f"
> as IDENT and the yacc parser adds it to the symbol table. On the second
> instance, flex will identify "f" as TYPE, which triggers an error case
> in the yacc parser. Given that TYPE would have been IDENT had it not
> been in the symbol table, the the segmentaion fault could be avoided by
> treating TYPE as IDENT in the affected rule.
> 
> Some might consider placing identical function pointer type declarations
> in different headers to be poor style might consider a failure to be
> beneficial. However, failing through a segmentation fault makes the
> cause non-obvious and can waste the time of anyone who encounters it.
> 
> Signed-off-by: Richard Yao <richard.yao@...sterhq.com>
> Acked-by: Madhuri Yechuri <madhuriyechuri@...sterhq.com>

Applied to kbuild.git#kbuild.

Michal

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