Re: another conditional breakpoint question

[Peter Jay Salzman <p at dirac dot org>]

begin Daniel Jacobowitz <drow@mvista.com> 
> On Fri, Sep 20, 2002 at 01:13:04PM -0700, Peter Jay Salzman wrote:
> > in the program:
> > 
> >    #include <math.h>
> >    int main(void)
> >    {
> >         double i = 0.0;
> >         double j = cos(i);
> >         return 0;
> >    }
> > 
> > i set a breakpoint which should never be reached:
> > 
> > p@satan% gdb mymath
> > (gdb) break main if cos(0.0) > 1000.0
> > Breakpoint 1 at 0x8048426: file mymath.c, line 5.
> > 
> > (gdb) run
> > Breakpoint 1, main () at mymath.c:5
> > 5               double i = 0.0;
> > 
> > considering that cosine should be greater than 1 for a real variable,
> > this is quite strange!
> > 
> > 
> > i don't know if this is related, but i notice that cos(0) doesn't have a
> > value of 1.0.  not even close:
> > 
> >    (gdb) p cos(0)
> >    $3 = 14368
> > 
> > but just in case gdb doesn't know that cos() returns a double, i also
> > tried:
> > 
> >    (gdb) p/f cos(0.0)
> >    $1 = 2.00890148e-41
> > 
> > neither of these are even close to being right.
> > 
> > 
> > can someone tell me why gdb is reaching that breakpoint which should
> > never be reaced?  and is there any way of getting gdb to tell me that
> > cos(0) is supposed to be equal to 1?   :*)
> 
> You don't have debug information in your libraries.  Try:
> 
> (gdb) ptype cos
> 
> to see what I mean.  You need debugging info if you want that to wokr.
 
hi daniel,

i see what you mean.  but then i'm confused why strlen works.

   18      int main(void)
   19      {
   20              char *string = "GNU/Linux";
   21              char revstring[255];
   22
   23              reverse(string, revstring);
   24              printf("%s\n", revstring);
   25
   26              return 0;
   27      }
   
   (gdb) break 21 if strlen(string) == 9
   Breakpoint 3 at 0x8048440: file string_reverse.c, line 21.
   
   (gdb) run
   Starting program: /home/p/writing/ddd/src/string_reverse 
   
   Breakpoint 3, main () at string_reverse.c:23
   23              reverse(string, revstring);


i have libc6 and libc6-dev installed on my system, but not libc6-dbg.
other string stuff works to, like:

   break main if ! strcmp("hello", "hello")

considering that i don't have the dbg versions of either libm or libc6,
do you have any idea why the string functions would work in the
conditionals but not the math functions?

thanks!
pete

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