Broken autoconf mmap test (was Re: 1.7] BUG - GREP slows to a crawl with large number of matches on a single file)

Sun Nov 8 16:12:00 GMT 2009

On Sun, Nov 08, 2009 at 10:51:56AM -0500, Ralph Hempel wrote:
>Corinna Vinschen wrote:
>> On Nov 8 14:56, Corinna Vinschen wrote:
>>> Btw., the check for mmap in grep's configure file is broken. It tries
>>> to mmap to a fixed address formerly allocated via malloc(). This doesn't
>>> work on Windows. An autoconf run with a newer version of autoconf would
>>> be nice.
>>>> I just found that the latest autoconf *still* has this broken test
>> for mmap, which basically calls
>>>> data2 = malloc (size);
>> mmap(data2, ...);
>>>> Why has this test never been fixed? Chuck?
>>I can't answer that question but this thread points out very important
>lessons in debugging specifically and projects in general.
>>1. Easily reproducible test cases are critical to getting somone
> interested in fixing your problem.
>>2. Having the good fortune to have somebody run the test case and
> duplicate the problem helps a bit more.
>>3. Having that person challenge the assumptions under which the code
> has been working for YEARS without a complaint helps a bit more.
>>4. Having that person do a great analysis that shows why the problem
> exists helps even more.
>>5. Going even one step further and trying to figure out why the
> problem has existed for years and what else might be wrong is
> just the icing on the cake.
>>Bravo Corinna - on a Sunday no less...

6. googling for the problem is always a good thing to do.
Once it was clear that this was a character set issue in grep it was
easy enough to find a fix since it was already in a couple of linux bug
trackers.
cgf
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