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Re: rules for conditional breakpoints
On Wed, Sep 25, 2002 at 11:40:06PM -0700, Peter Jay Salzman wrote:
> hi eli,
>
> unfortunately, the user manual doesn't really say much about this. the
> relevent section is 5.1.6 (break conditions) which references section
> 8.1 (expressions).
>
> in the first paragraph os 5.1.6:
>
> A condition is just a Boolean expression in your programming language
> (see section 8.1 Expressions).
>
> but this is where my confusion is coming from. here is a boolean
> expression:
>
> break main if cos(0.0) == 1.0
>
> the condition "cos(0.0) == 1.0" is a boolean expression. it's either
> true or false. yet it's not valid in a conditional breakpoint.
If you had debugging information in your library, it would work, as I
tried to explain last time. Or you can do this:
(gdb) set $p = (double (*) (double)) cos
(gdb) ptype $p
type = double (*)()
(gdb) p cos(2.)
$2 = 14880
(gdb) p $p(2.)
$4 = -0.41614683654714241
> looking further down the section 5.1.6, it mentions that user defined
> functions are allowed in conditions.
>
>
>
> looking at section 8.1, it has something relevent:
>
> Any kind of constant, variable or operator defined by the programming
> language you are using is valid in an expression in GDB. This
> includes conditional expressions, function calls, casts and string
> constants. It unfortunately does no include symbols defined by
> preprocessor #define commands.
That's out of date. Macros work now if you have the right debug info.
> this is kind of ambiguous whether "the programming language" includes
> glibc or not. if it doesn't, then i'm unsure what "functions" this
> paragraph is talking about. if it does, then it directly conflicts with
> my "cos(0.0) == 1.0" as an example of something that should work but
> doesn't.
Perhaps it could be clearer. What it means is, the _concept_ of a
function call, as an operation, is valid. The function you call has to
be defined with debug info. This is actually misleading since a lot of
what is in glibc is specified by the language standard...
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer