[DTrace-devel] [PATCH v2] dtprobed: use /proc/$pid/map_files, not the filename of the mapping

[Kris Van Hees]

Here is the problem:

        prf = mapp->pr_file;
        if (prf == NULL || (mapp = prf->first_segment) == NULL) { 
                fuse_log(FUSE_LOG_ERR, "%i: dtprobed: cannot look up mapping (process dead?)\n",
                         pid);
                goto out;
        } else if ((fn = Pmap_mapfile_name(P, mapp)) == NULL) {
                fuse_log(FUSE_LOG_ERR, "%i: dtprobed: cannot look up mapname (process dead?)\n",
                         pid);
                goto out;
        }
        mod = strrchr(fn, '/');
        if (mod)
                mod++;
        else
                mod = fn;

Since you changed this to get the mapping filename in map_files, you get a
name that has the address range as its filename, and since that gets used as
the module name, you end up with the wrong module name in the probe spec.

It needs to be the actual filename of the source file that the mapping came
from.

On Thu, Feb 12, 2026 at 06:18:25PM +0000, Nick Alcock wrote:
> On 12 Feb 2026, Eugene Loh outgrape:
> 
> > I do not know what went wrong here.  I would have bet big money that I
> > tested this, but here is what I find now with this patch:
> 
> So did I!
> 
> > test/unittest/usdt/tst.enabled.sh: Running timeout --signal=TERM 41 test/unittest/usdt/tst.enabled.sh /home/.../build/dtrace
> > FAIL: expected results differ.
> > 400000-401000:main:go
> >
> > Diff against expected:
> > --- test/unittest/usdt/tst.enabled.r    2026-02-12 05:31:24.000000000 +0000
> > +++ /tmp/runtest.6196/test.out  2026-02-12 18:09:58.980466976 +0000
> > @@ -1,2 +1,2 @@
> > -test:main:go
> > +400000-401000:main:go
> 
> This suggests that symbol lookup is failing, which it shouldn't be,
> because that *too* uses /proc/$pid/map_files, or should.
> 
> I clearly need to debug this. Got a system on which it goes wrong?