question about conditional breaking

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

dear gdb mailing list,

the gdb user's manual doesn't have a lot to say about conditional
breaking, but i think i'm beginning to understand it more thoroughly.

first, we know that the boolean expressions you'd expect to be able to
use, work as advertised.

break 1 if x > 0
break 2 if y <= x

parenthesis seem to be purely optional.

break 3 if (! x >= -1)


but there seems to be more to the story.  you can use functions too.
here's a test program:

#include <math.h>

int main(void)
{
   double l = cos(i);
   double m = y0(i);

   return 0;
}


where y0 is a bessel function of the 2nd kind (a von neumann function)
of the zeroth order.

it seems like you can use functions, like math library functions.  but
with a privisio:

   (gdb) break main if cos(3) == 0
   Breakpoint 1 at 0x8048456: file math.c, line 5.
   
   (gdb) break main if sin(3) == 0
   No symbol "sin" in current context.
   
   (gdb) break main if exp(3) == 0
   No symbol "exp" in current context.
   
   (gdb) break main if y0(3) == 0
   Note: breakpoint 1 also set at pc 0x8048456.
   Breakpoint 2 at 0x8048456: file math.c, line 5.
   
   (gdb) break main if y1(3) == 0
   No symbol "y1" in current context.


so it appears that here's the rule:

you're allowed to use any function, even library functions, provided that:

1. the library is linked to your application
2. you actually _use_ the function somewhere in your code.

to be honest, i'm not the least surprised by condition 1, but i'm
shocked by condition 2.


does anyone have anything to add to this?  am i on the right track here?

pete

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