Re: patch 2/2 debuginfod server etc.

[Mark Wielaard <mark@klomp.org>]

Hi Frank,

On Fri, 2019-11-15 at 16:00 -0500, Frank Ch. Eigler wrote:
> > > +  string popen_cmd = string("/usr/bin/rpm2cpio " +
> > > shell_escape(b_source0));
> > 
> > Why the hardcoded path?
> > Could you check at startup if rpm2cpio is in the PATH?
> 
> Hm, since this is run under popen(), so it'll do $PATH searching for
> us.  Checking whether it is present at runtime ... hmmm ugh ... how
> about an autoconf test instead?  The worst thing that happens with
> the
> current code is that on a non-rpm system, if it does find .rpm files,
> the code will print errors and otherwise ignore RPMs.

OK, I think how you did it on the branch, just remove the path, let the
shell find rpm2cpio, is fine for now.

> > > +      // extract this file to a temporary file
> > > +      char tmppath[PATH_MAX] = "/tmp/debuginfod.XXXXXX"; // XXX:
> > > $TMP_DIR etc.
> > 
> > Some other code uses:
> >   const char *tmpdir = getenv ("TMPDIR") ?: P_tmpdir;
> >   static const char suffix[] = "/debuginfod.XXXXXX";
> > Also PATH_MAX?
> 
> OK -- and yeah if we getenv() we might need PATH_MAX.
> Will try asprintf() here and the client instead.

It would be really nice if this code at least respected TMPDIR.

> > Also I prefer checking against NULL, it is slightly more obvious (0
> > returns  often means success).
> 
> ... the C++ tradition is 0 for null pointers, but if you insist...

No, if that is the C++ way then that is fine.

> > > +  Dwarf_Off offset = 0;
> > > +  Dwarf_Off old_offset;
> > > +  size_t hsize;
> > > +
> > > +  while (dwarf_nextcu (dbg, old_offset = offset, &offset, &hsize, NULL, NULL, NULL) == 0)
> > 
> > These days I would prefer dwarf_get_units (). It is slightly higher
> > level and immediately gives you the cudie and unit_type.
> 
> Will look into that later.
>
> > > +    {
> > > +      Dwarf_Die cudie_mem;
> > > +      Dwarf_Die *cudie = dwarf_offdie (dbg, old_offset + hsize, &cudie_mem);
> > > +
> > > +      if (cudie == NULL)
> > > +        continue;
> > > +      if (dwarf_tag (cudie) != DW_TAG_compile_unit)
> > > +        continue;
> > > +
> > > +      const char *cuname = dwarf_diename(cudie) ?: "unknown";
> > > +
> > > +      Dwarf_Files *files;
> > > +      size_t nfiles;
> > > +      if (dwarf_getsrcfiles (cudie, &files, &nfiles) != 0)
> > > +        continue;
> > 
> > So you are really only interested in the file/line tables.
> > In that case you could also use dwarf_next_lines which iterates through
> > the debug line units directly, so you don't need to do the whole CU DIE
> > tree iteration yourself (and it handles CUless tables).
> 
> Ditto.

I believe the code works as is, so it isn't urgent.
I just think it
would simplify things a bit.

> > > +          string waldo;
> > > +          if (hat[0] == '/') // absolute
> > > +            waldo = (string (hat));
> > > +          else // comp_dir relative
> > > +            waldo = (string (comp_dir) + string("/") + string (hat));
> > 
> > Do you have to think about/handle a comp_dir that ends with a / ?
> > Old debugedit truncated some strings by adding /// (to fill up the
> > spaces till the '\0'...) Yes, terrible :{
> 
> It should just work(tm) if the debugger uses the documented convention
> and preserves those extra slashes (just as if it preserved ../ and
> such).

See also the other email/review. So, we always add an '/' between
comp_dir and the file. That should probably be explicitly documented
because I wouldn't be surprised if some code doesn't when comp_dir
already ends in a slash.

I just double checked that dwarf_getsrclines always (unconditionally)
adds a '/', so the use of dwarf_filesrc here does the right thing.

Thanks,

Mark