[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

GDB testsuite overrides default_target_compile and breaks

From: Jacob Bachmeyer
Subject: GDB testsuite overrides default_target_compile and breaks
Date: Wed, 10 Jun 2020 21:43:48 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20090807 MultiZilla/ SeaMonkey/1.1.17 Mnenhy/

[previous Subject: Re: dejagnu version update? [CORRECTION: not a regression in DejaGnu; GDB testsuite bug] ]
[adding Tom Tromey to CC list per advice from Rob Savoye]
[adding main DejaGnu mailing list to CC list]

In brief for those new to this, the GDB testsuite is currently broken when run with the current DejaGnu Git master. The problem was initially reported off-list and traced to a copy of default_target_compile in the GDB testsuite. A recent change to DejaGnu internals included a change to that procedure upstream. Cleanup enabled by that change breaks the old copy of the code in the GDB testsuite.

What is needed in brief:
(1) Merge the features of default_target_compile that the GDB testsuite depends on upstream for 1.6.3. (2) Find the actual extensibility that GDB needs here and add that support to the default_target_compile rewrite slated for 1.6.4.

Maciej W. Rozycki wrote:
[cc-ing Joel as the originator, and <>]

On Tue, 9 Jun 2020, Jacob Bachmeyer wrote:
I ran a quick bisection and the culprit turned out to be:

ba60272a5ac6f6a7012acca03f596a6ed003f044 is the first bad commit
commit ba60272a5ac6f6a7012acca03f596a6ed003f044
Author: Jacob Bachmeyer <>
Date:   Mon May 25 08:40:46 2020 -0600

Establish a default C compiler by evaluating [find_gcc] if no other compiler is given.

 So this regression has to be fixed before any new release is made.
I will look into this. So far, I have confirmed that the problem does occur and that setting the "compiler" board_info key in baseboards/unix.exp seems to avoid it. It looks like the default is not being selected in all cases where it should be used. I still need to find the exact problem to write a regression test to isolate this bug and make it stay squashed.
After further efforts, and a few hours wasted trying to figure out why additional tracing code added to default_target_compile was not producing output, I eventually decided to just make default_target_compile throw a Tcl error -- and I did not get a Tcl error when running the tests...

That is "very interesting" and a quick grep -R reveals the culprit: the GDB testsuite is overriding default_target_compile in gdb/testsuite/lib/future.exp. Comments indicate that that file was intended to temporarily bundle certain features with the GDB testsuite that had not yet been merged into upstream DejaGnu -- in 2004. Now DejaGnu core is continuing to develop, leaving the old code copied into the GDB testsuite broken, and making this NOTOURBUG.

Well, as the name suggests (regrettably there's no adequate documentation there) this procedure is there to be overridden.

No, *_hook indicates a procedure that is there to be overridden, but not by testsuites. Overriding procedures inside DejaGnu is generally for testing lab customization, because a site can update their init files when they update DejaGnu, but testsuites need to work with multiple versions of DejaGnu.

The way it's done in GDB might perhaps be non-standard, as the standard way AFAICS would be by providing a `gdb_compile' handler, but I think this is tangential, and the chosen solution is there possibly because DejaGnu had no `${tool}_compile' knob back then (I haven't checked). That does not really matter though, as the net effect would be the same.

DejaGnu does not have a ${tool}_compile -- that would be a legitimate procedure for a testsuite to define and use, and I believe that the GDB testsuite does so. There is a ${target}_compile customization point that is intended for testing labs to override for specific target boards. (It is not quite correctly handled in target_compile at the moment, but this is slated to be fixed for 1.6.4.) The default_target_compile procedure is intended to be the default handler for target_compile for targets that do not have their own special compilation procedures.

In short, this is not a regression in DejaGnu; this is code duplicated into the GDB testsuite that was slated for removal from that location years ago and needs to be removed from the GDB testsuite, or at least made conditional on running under a version of DejaGnu old enough to require it, if such versions are still supported for running the GDB testsuite. If that code has added features not present in upstream DejaGnu over the years, now is the time to get those patches in.

Well, it clearly is a functional regression as the interface has changed, even if not a formal one, and I would consider it a release stopper.

The changes were to an internal component and broke an out-of-tree copy of same. I have to draw a line somewhere, and "monkeypatching the core is not supported and can break" is necessary for DejaGnu to develop at all. Add that comments in gdb/testsuite/lib/future.exp clearly state (from 2004! 16 years ago!) that that entire file was supposed to only temporarily exist until its features were merged upstream and I say that now is the time to pick that dropped ball back up and get those features merged upstream.

As it happens there are about 2 users of DejaGnu there, which means any fatal regression would have been easily caught in the course of change verification (and running binutils/GDB and GCC test suites natively is about as easy as it can be: `configure && make && make check'), and indeed should have, and then sorted with the respective communities if indeed the interface change is unavoidable, with a transition period so that the users can prepare changes to their frameworks, including backports to various release branches if applicable, before the old interface is removed from DejaGnu.

There will certainly be a lengthy deprecation process for the planned future API cleanups; indeed, the difference between the last release in 1.x and 2.0 is planned to be the removal of compatibility shims, but that is still very far off.

My suggestion would be to revert the change, get the details sorted with GDB people and only reapply it when all parties are ready.

The actual change that broke the out-of-tree copy of default_target_compile was cleaning up the board files to remove the now-optional definition of the "compiler" board_info key. (Some testsuites do not need to compile code and running find_gcc emits useless "verbose noise" in those cases.) A patch to revert this clean up (but not the addition of [find_gcc] as default in default_target_compile) may be reasonable on the release branches for the remaining 1.6.x releases, since it would not significantly affect the core, but the change stays on the master branch. Monkeypatching the DejaGnu core is not supported and cannot be supported long-term. (In the future, default_target_compile may eventually disappear from the global namespace as seen by testsuites. If GDB continues to override it, the rename will end up deleting the compatibility shim while the internal calls still go to the internal copy of the procedure. Then it all blows up with a Tcl error in DejaGnu 2.0 when the compatibility shim is removed.)

GDB seems to have also extended default_target_compile, so a discussion on this is needed because there seems to be a need for some kind of language extensibility feature to allow new language-default-selector options to be defined without overriding the entire default_target_compile procedure (which could also break in a test lab that uses a custom ${target}_compile procedure for a certain board). Since default_target_compile is slated to be rewritten between 1.6.3 and 1.6.4, now is a very good time to get additional features that it needs to have into the DejaGnu core. The API is now documented as "target_compile" in Git master. Backwards-compatible extensions (like adding new language default options) are possible, of course.

If I understand correctly, merging the features currently carried in gdb/testsuite/lib/future.exp upstream will cause all existing GDB releases to correctly use the upstream version of default_target_compile, making the partial reversion patch unnecessary.

Anyway, I have completed the verification I have volunteered to do and therefore I'm done with my part.

Thank you for your help. [To Maciej W. Rozycki: The requests for further efforts in this email are for other people who work more closely with GDB.]

-- Jacob

reply via email to

[Prev in Thread] Current Thread [Next in Thread]