Strange effect in GDB 6.8 when setting breakpoint on symbol with both strong and weak definitions

Antony KING
2008-10-14T13:24:49Z

Consider the following source files a.c and b.c:

== a.c ==
#include <stdio.h>
void f(void) __attribute__((weak));
void f(void)
{
printf("FAIL\n");
}
int main(void)
{
f();
return 0;
}
== a.c ==
== b.c ==
#include <stdio.h>
void f(void)
{
printf("PASS\n");
}
== b.c ==

If I compile them (on RHEL3 but I don't think this is significant) using
"gcc -g a.c b.c" and then debug the resulting executable using the
following GDB script:

file a.out
set trace-commands 1
break f
tbreak main
info breakpoints
run
info breakpoints
break f
continue

I see the following output from GDB:

> +break f
> Breakpoint 1 at 0x8048382: file b.c, line 5.
> +tbreak main
> Breakpoint 2 at 0x8048369: file a.c, line 11.
> +info breakpoints
> Num Type Disp Enb Address What
> 1 breakpoint keep y 0x08048382 in f at b.c:5
> 2 breakpoint del y 0x08048369 in main at a.c:11
> +run
> main () at a.c:11
> 11 f();
> +info breakpoints
> Num Type Disp Enb Address What
> 1 breakpoint keep y 0x0804834a in f at a.c:5
> +break f
> Breakpoint 3 at 0x804834a: file a.c, line 6.
> +info breakpoints
> Num Type Disp Enb Address What
> 1 breakpoint keep y 0x0804834a in f at a.c:5
> 3 breakpoint keep y 0x0804834a in f at a.c:6
> +continue
> PASS
>
> Program exited normally.

As you can see the location of the breakpoint at f() has been shifted
from its definition in b.c (which is what I expected) before the program
is run, to its definition in a.c after the program stopped in main()
(which is not what I would expect). This shift of location seems wrong
to me and quite unexpected. Is this a bug ?

Another problem is that although there are 2 definitions of f() in the
program, only 1 breakpoint is being set. My understanding is that GDB
should set multiple breakpoints on f(). Is this correct (or is this only
a feature that is enabled when debugging C++ applications) ?

[The application I am trying to debug is more complicated embedded
application running on an SH-4 CPU but the example above illustrates the
problems I am encountering.]

Thanks for any illumination.

Cheers,

Antony.