Re: add set cp-abi command

Jim Ingham
2002-03-14T21:14:17Z

Daniel,

On Wednesday, March 13, 2002, at 12:11 PM, Daniel Jacobowitz wrote:

> On Wed, Mar 13, 2002 at 10:56:22AM -0800, Jim Ingham wrote:
>> Hi, all...
>>
>> gdb assumes that it will never see a mix of gcc2 & gcc3 compiled C++
>> code in a single executable. So it determines which abi to use by
>> setting it to gnu-v2, and then if it EVER sees a v3 style mangled name,
>> it switches it to v3. This breaks down in the case where you have some
>> shared libraries compiled with gcc3, but the user code is compiled with
>> gcc2. This is a perfectly okay thing to do if the libraries don't
>> export any C++ symbols, but gdb will get the abi wrong, and you won't
>> be
>> able to print any C++ objects in the user code. Ouch!
>>
>> I am not currently proposing any fancy mechanism to try to switch on
>> the
>> fly between the two. The problem is temporary so I don't really think
>> it is worth the effort to cook up such a scheme. Rather, I just
>> added a
>> "set cp-abi" command so that my users can fix the problem by hand when
>> they notice it arising.
>
> We could reasonably have an ABI per-objfile. In fact, we probably
> should... it's not clear how that would interact with this patch. But
> I'm not going to ask you to do that.

Thanks... I am not sure it is really worth the effort. It is not
really something we want to encourage folks to do, after all, and in
time the issue will fade away...

>
> I think it might be wiser to have cp-abi default to "auto" and
> condition the autoselection magic based on that. Otherwise, if you set
> it to v2, it is likely to autorevert to v3 unexpectedly. Could you add
> that change?

Okay. I almost got this working last night, and thought I would have
time to finish it today, but got hung up on some other emergency...

>
>> 2002-03-12 James Ingham <jingham@apple.com>
>>
>> * cp-abi.c (set_cp_abi_cmd, show_cp_abi_cmd,
>> show_cp_abis_cmd): New functions, allow you to set & show
>> cplus abi's in case gdb gets it wrong.
>> (_initialize_cp_abi): Define the cp-abi switching commands.
>
> Also, a couple of small changes (below).
>
>> ***************
>> *** 103,109 ****
>> --- 106,164 ----
>> int i;
>> for (i = 0; i < num_cp_abis; i++)
>> if (strcmp (cp_abis[i].shortname, short_name) == 0)
>> + {
>> current_cp_abi = cp_abis[i];
>> return 1;
>> + }
>> +
>> + return 0;
>> + }
>
> Indentation, of course.

This is actually mailer mangling, it was right in the sources. $%#$#$$#
GUI mailers...

>
>> +
>> + void
>> + set_cp_abi_cmd (char *args, int from_tty)
>> + {
>> +
>> + if (!switch_to_cp_abi (args))
>> + error ("Could not find ABI: \"%s\" in ABI list\n", args);
>> + }
>> +
>> + void
>> + show_cp_abi_cmd (char *args, int from_tty)
>> + {
>> + ui_out_text (uiout, "The current cplus abi is: ");
>
> "currently selected C++ ABI", please.

As you wish...

>
>> +
>> + ui_out_field_string (uiout, "cp-abi", current_cp_abi.shortname);
>> + ui_out_text (uiout, ".\n");
>> + }
>> +
>> + void
>> + show_cp_abis_cmd (char *args, int from_tty)
>> + {
>> + int i;
>> + ui_out_text (uiout, "The valid cplus abi's are:\n");
>
> "C++ ABIs" (or ABI's? ABIs, I think, if there isn't a precedent)

We actually checked Strunk & White, and as of the mid 30's, this should
be ABIs...

>
>> +
>> + ui_out_tuple_begin (uiout, "cp-abi-list");
>> + for (i = 0; i < num_cp_abis; i++)
>> + {
>> + ui_out_field_string (uiout, "cp-abi", cp_abis[i].shortname);
>> + ui_out_text (uiout, "\n");
>> + }
>> + ui_out_tuple_end (uiout);
>> +
>> + }
>> +
>> + void
>> + _initialize_cp_abi (void)
>> + {
>> + struct cmd_list_element *cmd;
>> +
>> + cmd = add_cmd ("cp-abi", class_obscure , set_cp_abi_cmd,
>> + "Set the ABI used for inspecting C++ objects",
>> &setlist);
>> +
>> + cmd = add_cmd ("cp-abi", class_obscure, show_cp_abi_cmd,
>> + "Show the ABI used for inspecting C++ objects",
>> &showlist);
>> + cmd = add_cmd ("cp-abis", class_obscure, show_cp_abis_cmd,
>> + "List the available ABIs for inspecting C++ objects",
>> &showlist);
>
> I believe 'show cp-abi' should show the available ABIs. That's more in
> keeping with existing code.

How would you find out the current ABI, then? Probably better is to
chuck the show abis, and let "set cp-abi" (with no arguments) perform
this function. This is the way "set language" works, so it has
precedent. I was sure that there was another command that used the
singular lists current, plural lists all, but I can't find it so maybe I
was just out of my mind...

Jim
--
Jim Ingham jingham@apple.com
Developer Tools - gdb
Apple Computer