[Libguestfs] [PATCH libnbd 0/3] generator: Reset line directive after included code in lib/states.c

[Eric Blake]

On Fri, Dec 03, 2021 at 07:11:46PM +0000, Richard W.M. Jones wrote:
> On Fri, Dec 03, 2021 at 07:02:07PM +0000, Richard W.M. Jones wrote:
> > This restores the #line directives (probably?)  The output looks
> > right, but I didn't test it beyond opening it in the editor.  Do #line
> > directives have a way to indicate "current file"?
> 
> What I mean is that if you have:
> 
> lib/states.c ----------------------------------------
>   #line 10 "generator/states.c"
>   ...
>   #line 20
> --------------------
> 
> does the second #line refer to generator/states.c or lib/states.c?

Alas, generator/states.c.  Here's how I tested.  In particular, note
that you MUST use an off-by-one #line directive for the current file
(the directive #line 10 must appear on line 9, for gdb to display the
code at line 10 on the next step of the program).

$ cat foo.c
#include <stdio.h>

int main(void)
{
    int i = 1;
#line 1 "bar.c"
    i++; // real line 7
    i++; // real line 8
#line 10
    i++; // real line 10
    i++; // real line 11
#line 13 "foo.c"
    i++; // real line 13
    printf("%d\n", i);
    return 0;
}
$ cat bar.c
i--; // fake line 1
i--; // fake line 2
i--; // fake line 3
i--; // fake line 4
i--; // fake line 5
i--; // fake line 6
i--; // fake line 7
i--; // fake line 8
i--; // fake line 9
i--; // fake line 10
i--; // fake line 11
i--; // fake line 12
i--; // fake line 13
i--; // fake line 14
i--; // fake line 15
$ gcc -g -o foo -Wall foo.c
$ gdb ./foo
GNU gdb (GDB) Fedora 11.1-5.fc35
...
(gdb) b main
Breakpoint 1 at 0x40112e: file foo.c, line 5.
(gdb) r
Starting program: /home/eblake/libnbd/foo 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Breakpoint 1, main () at foo.c:5
5	    int i = 1;
(gdb) n
1	i--; // fake line 1
(gdb) 
2	i--; // fake line 2
(gdb) 
10	i--; // fake line 10
(gdb) 
11	i--; // fake line 11
(gdb) 
13	    i++; // real line 13
(gdb) 
14	    printf("%d\n", i);
(gdb) 
6
15	    return 0;
(gdb) c
Continuing.
[Inferior 1 (process 3800760) exited normally]
(gdb) q



-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org