Re: C compiler issue perhaps?
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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Re: C compiler issue perhaps?
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.
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Re: C compiler issue perhaps?
At 12:02 PM 3/15/2008, Chuck Robey wrote:
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
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.
2points:
(1) yes, you are right, without the source code, any guesses are at the
same level as black magic, useless
(2) if the user is learning to use gdb, then it is really bad manners to
suggest that printfs should be used. While I have made massive use
of printfs before I got used to gdb, gdb is incredibly more powerful,
can do any and all that any prints might accomplish, and anyone who
is willing to learn to use that debugger should be encouraged, not
given bad habits that really should be a fallback only to environments
where gdb won't work.
Chuck,
On your point 2 let me say that there are simply times when a developer
needs to check run-time code versus running the code in a
debugger. Debuggers are a great tool, but they do cause some side-effects
as was noted in the original post. If the debugger is not consistent in
the variable values, it is of little use if those values are causing a
problem. What I originally suggested was using conditionally compiled
fprintf's to check those variable values running the program by itself
instead of inside gdb. I know adding additional code, even just fprintf's,
can change the way a program is compiled and optimized. But this at least
gives another way to validate the variables.
-Derek
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Re: C compiler issue perhaps?
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1
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.
2points:
(1) yes, you are right, without the source code, any guesses are at the
same level as black magic, useless
(2) if the user is learning to use gdb, then it is really bad manners to
suggest that printfs should be used. While I have made massive use
of printfs before I got used to gdb, gdb is incredibly more powerful,
can do any and all that any prints might accomplish, and anyone who
is willing to learn to use that debugger should be encouraged, not
given bad habits that really should be a fallback only to environments
where gdb won't work.
>
> -Derek
>
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Re: C compiler issue perhaps?
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.
-Derek
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Re: C compiler issue perhaps?
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.
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Re: C compiler issue perhaps?
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.
-Derek
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Re: C compiler issue perhaps?
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
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Re: C compiler issue perhaps?
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
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C compiler issue perhaps?
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.
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