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Re: SEGFAULT if bash script make "source" for itself


From: Eric Blake
Subject: Re: SEGFAULT if bash script make "source" for itself
Date: Thu, 28 Aug 2014 16:32:06 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0

On 08/28/2014 04:11 PM, address@hidden wrote:
>> If gcc segfaults because it implements #include via recursion, and I
>> wrote a recursion loop of #includes into my source, then I'd say the bug
>> was mine, not gcc's.  Just the same as if you write a recursion loop
>> into your bash program.
>>
>> It's not the compiler's fault that input that requests recursion can
>> abuse the stack.  Rather, it is the fault of the input.
>>
> Unhanded program termination - is not input problem, it is program problem.
> 
> Looks like gcc programmers not so dumb.
> 
> $ gcc a.c
> In file included from a.h:1:0,
...
>                  from a.h:1,
>                  from a.c:1:
> a.h:1:15: error: #include nested too deeply

If you think the gcc programmers have imposed an artificial limit, raise
a bug report on their list.  Although the GNU Coding Standards request
no artificial limits, we cannot enforce what other programs choose to do
or not do by having a conversation on this list.

Also, it's not obvious whether gcc actually implements includes via
recursion, or whether it uses some other means - so even if they lifted
their limit for how much is too much include nesting, it's not readily
obvious whether that would turn into a stack overflow or a more generic
out of memory error.

Furthermore, the C language standard documents that compilers must allow
at least a certain amount of nesting, and declares that programs written
with more than that level of nesting are not strictly defined, and
therefore a compiler can do what it wants when it gets past that limit.
 Arguably, the fact that gcc errors out gracefully is a product of the
language definition that they are parsing - the language itself imposes
a design limit, and once you go beyond the guarantees of the language,
the compiler does not have to recurse forever.  But there is no such
comparable wording in POSIX for a minimum level of mandatory recursion
support in the shell.

> 
> I should make patch and add libsigsegv?

Patches speak louder than words in open source projects.  If you are up
to taking on the task, go for it.  You can use GNU m4 and gawk as
examples of programs that have integrated in libsigsegv stack overflow
detection.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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