Date: Mon, 17 Mar 2008 09:37:53 -0500 From: Derek Ragona <derek@computinginnovations.com> To: Doug Hardie <bc979@lafn.org> Cc: freebsd-questions <freebsd-questions@freebsd.org> Subject: Re: C compiler issue perhaps? Message-ID: <6.0.0.22.2.20080317093201.0261ec08@mail.computinginnovations.com> In-Reply-To: <59E2AE8C-70D4-49C8-B495-0F7CCCB042DB@lafn.org> References: <A768FF06-4601-42C6-A491-634F5135DCCD@lafn.org> <6.0.0.22.2.20080314171533.023f7c88@mail.computinginnovations.com> <511EC772-36FD-4799-B4A1-3AE690B6D048@lafn.org> <6.0.0.22.2.20080314202817.025de470@mail.computinginnovations.com> <EE488DB7-2E54-48F5-A3E2-1357BF848978@lafn.org> <6.0.0.22.2.20080315075146.02610a20@mail.computinginnovations.com> <59E2AE8C-70D4-49C8-B495-0F7CCCB042DB@lafn.org>
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At 12:29 AM 3/17/2008, Doug Hardie wrote:
>On Mar 15, 2008, at 05:59, Derek Ragona wrote:
>
>>At 09:49 PM 3/14/2008, Doug Hardie wrote:
>>
>>>On Mar 14, 2008, at 18:31, Derek Ragona wrote:
>>>
>>>>At 06:56 PM 3/14/2008, Doug Hardie wrote:
>>>>>There is no code running at that point. Its just sitting there
>>>>>waiting for me to enter a gdb command.
>>>>>
>>>>>
>>>>>On Mar 14, 2008, at 15:16, Derek Ragona wrote:
>>>>>
>>>>>>At 05:10 PM 3/14/2008, Doug Hardie wrote:
>>>>>>>I have a program I was testing with gdb. I was trying to figure
>>>>>>>out
>>>>>>>why c.rmonths was always zero when it should have been 6.
>>>>>>>Stepped
>>>>>>>through using the gdb n command. Here is the output:
>>>>>>>
>>>>>>>(gdb)
>>>>>>>215 c.rmonths = (edate - tdate) /
>>>>>>>toMONTHS;
>>>>>>>(gdb)
>>>>>>>223 c.dial_in = u.dial_in[0];
>>>>>>>(gdb)
>>>>>>>224 c.dsl = u.dsl[0];
>>>>>>>(gdb) p c.rmonths
>>>>>>>$1 = 0
>>>>>>>(gdb) p c
>>>>>>>$2 = {fa = 0, pwp = 0, disp_email = 0, imonths = 0, rmonths = 6,
>>>>>>> type = 73 'I', cd = 0 '\0', dial_in = 82 'R', dsl = 0 '\0',
>>>>>>> dsl_kit = 0 '\0', ip = 0 '\0', domain = 0 '\0', n_domain = 0
>>>>>>>'\0',
>>>>>>> renewal = 89 'Y', program = "I\000\000"}
>>>>>>>(gdb) p c->rmonths
>>>>>>>$3 = 6
>>>>>>>(gdb) p c.rmonths
>>>>>>>$4 = 6
>>>>>>>
>>>>>>>
>>>>>>>Notice, the first time i print it its zero. The second time
>>>>>>>its 6.
>>>>>>>What gives here? I have seen this before but couldn't pin it
>>>>>>>down.
>>>>>>>The program is not compiled with any optimization. It is in a
>>>>>>>shared
>>>>>>>library though.
>>>>>>
>>>>>>It is hard to tell without the code you used. I would put some
>>>>>>printf's in the code and see what and when that variable gets
>>>>>>set to
>>>>>>in actual running code.
>>>>>>
>>>>>> -Derek
>>>>
>>>>I understand it is waiting at a breakpoint in gdb. What I meant was
>>>>put printf's in your code and run the program and look at the
>>>>output. You can use fprintf's to stderr if your prefer and just
>>>>look at the stderr output.
>>>>
>>>>It is hard to diagnose what could be a compiler error, or a coding
>>>>error. Remember in C you can do many things you really shouldn't.
>>>>It is also advisable to run lint over your source code too.
>>>
>>>All that lint shows is it doesn't like comments using // and lots of
>>>errors in /usr/include files.
>>
>>This sounds more like a c++ program. c++ does a lot of variable
>>initiation in code you usually won't see.
>>
>>If this is a c++ program, put conditional printf's or cout's in to
>>check the code at actual runtime rather than in the debugger.
>>
>>You may want to use asserts.
>
>Nope. Very simple c code. I believe as was pointed out earlier that
>this is a gdb issue. Once gdb found the right value, both it and all
>the printfs show the correct value. I changed nothing. I am a bit
>concerned since this is now in a production system that it may
>eventually start fail again which would have some serious consequences.
Doug,
That reason is why you should put asserts in your program. Also check your
/etc/make.conf file as well as your program's Makefile for any compiler
options you may be using.
Another option you may want to explore is trying a different version of
gcc. There are a few versions of gcc in the ports you can install and try
on your program.
-Derek
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