bogus bkpt, using #line directives

bogus bkpt, using #line directives

[Allen Hopkins]

I'm using gdb (6.1.1) to debug applications that are 
compiled from C++ code which is, in turn, generated from 
special higher-level code (whose source files have ".mmm" 
extensions).

I've inserted "#line" directives at each .cpp line that 
claim that that line is really from the .mmm file it was 
generated from.

Here's a snippet of code from P.cpp to talk about:

> #line 39 "/tmp/allenh/metro/examples/mgdb/P.mmm"
>               try {
> #line 41 "/tmp/allenh/metro/examples/mgdb/P.mmm"
>                 port1->writeInt(this, w);
> #line 42 "/tmp/allenh/metro/examples/mgdb/P.mmm"
>                 w = w + 1;
> #line 42 "/tmp/allenh/metro/examples/mgdb/P.mmm"
>               } catch (STUCK) {
 > ...

A breakpoint set at line 42 ends up in a bogus place:

(gdb) b P.mmm:41
Breakpoint 6 at 0x805edde: file P.mmm, line 41.
(gdb) b P.mmm:42
Breakpoint 7 at 0x804d54a: file P.mmm, line 42.
(gdb) info b
Num Type           Disp Enb Address    What
6   breakpoint     keep y   0x0805edde in P::thread() at 
P.mmm:41
7   breakpoint     keep y   0x0804d54a in ~node at P.mmm:42

The breakpoint at "~node" is just plain wrong.  The 
breakpoint is set correctly if the "#line" directives are 
removed and the breakpoints are set on the actual .cpp line 
numbers.

The program is very complex & I haven't yet been able to 
make a simple test case to demonstrate this.  I'm sort of 
desperately hoping this looks familiar to somebody who can 
offer me some hope, or suggestions.  I'm left wondering if I 
have to debug gdb, but I'd be in really unfamiliar territory.

-Allen

Re: bogus bkpt, using #line directives

[Daniel Jacobowitz]

On Thu, Dec 02, 2004 at 09:43:25AM -0800, Allen Hopkins wrote:
> The program is very complex & I haven't yet been able to 
> make a simple test case to demonstrate this.  I'm sort of 
> desperately hoping this looks familiar to somebody who can 
> offer me some hope, or suggestions.  I'm left wondering if I 
> have to debug gdb, but I'd be in really unfamiliar territory.

Start by debugging GCC's generated line table.  If you're using
DWARF-2, you can print it with readelf -wl.  Does it put line markers
in sensible places?

-- 
Daniel Jacobowitz