kernel generates spurious SIGTRAPs in debugged applications

[Frédéric RIss]

Binary package hint: linux-image-2.6.24-19-generic

--> lsb_release -rd
Description: Ubuntu 8.04.1
Release: 8.04

linux-image-2.6.24-19-generic version 2.6.24-19.36

Under some conditions, the kernel generates spurious SIGTRAPs when debugging a program. It seems the kernel executes PTRACE_SINGLESTEP instead of the requested PTRACE_CONTINUE. The easiest way to see this effect is in the GDB testsuite, in the shlib-call.exp test (I checked that the GDB package in hardy exposes this).

[Frédéric RIss (frederic-riss)]

Something wasn't very clear in what I said above. This isn't only some bizarre testsuite FAIL. This affects real life debugging. I can't debug my C++ code at all due to this bug. The bug manifests itself with some sequences of stepping and calling debuggee functions. It does it all the time when I debug C++ code because then the debugger calls functions for operators.

I'd just like to be sure that this bug doesn't get any answer because there're more serious issues than making some programs undebugable, and not because it looks like some totally theoretical issue.

[Leann Ogasawara (leannogasawara)]

The Ubuntu Kernel Team is planning to move to the 2.6.27 kernel for the upcoming Intrepid Ibex 8.10 release. As a result, the kernel team would appreciate it if you could please test this newer 2.6.27 Ubuntu kernel. There are one of two ways you should be able to test:

1) If you are comfortable installing packages on your own, the linux-image-2.6.27-* package is currently available for you to install and test.

--or--

2) The upcoming Alpha5 for Intrepid Ibex 8.10 will contain this newer 2.6.27 Ubuntu kernel. Alpha5 is set to be released Thursday Sept 4. Please watch http://www.ubuntu.com/testing for Alpha5 to be announced. You should then be able to test via a LiveCD.

Please let us know immediately if this newer 2.6.27 kernel resolves the bug reported here or if the issue remains. More importantly, please open a new bug report for each new bug/regression introduced by the 2.6.27 kernel and tag the bug report with 'linux-2.6.27'. Also, please specifically note if the issue does or does not appear in the 2.6.26 kernel. Thanks again, we really appreicate your help and feedback.

[Neil Munro (neilmunro-deactivatedaccount)]

The Intrepid Ibex 8.10 Beta release was most recently announced - http://www.ubuntu.com/testing/intrepid/beta . It contains the 2.6.27 Ubuntu kernel. It would be great if you could test and verify if this is still an issue. The status is being set to Incomplete until we receive further feedback. Thanks.

[Frédéric RIss (frederic-riss)]

I'll test as soon as I install the final Intrepid on one of my boxes.

However I'm quite disappointed about the way this bug is handled. It's a serious bug that most users will attribute to GDB being unable to debug C++ code. I've seen at least one user asking about it on the GDB development mailing list. You're aware that 99,9% of users won't even try to find the cause of the issue.

This bug is present in your LTS release and has been introduced by the Ubuntu specific patches... such failures in a mainline kernel would have been caught by the GDB guys (to be sure, I checked that vanilla 2.6.24 doesn't expose the issue). Moreover, I provided an easy way to reproduce.

As I said, I'll check soon after Intrepid final will be released, but I don't see how this will help fixing the bug in your LTS release :-(

[Dimitrios Symeonidis (azimout)]

Frederic, any news on this? Is this still an issue for you?

[Jeremy Foshee (jeremyfoshee)]

This bug report was marked as Incomplete and has not had any updated comments for quite some time. As a result this bug is being closed. Please reopen if this is still an issue in the current Ubuntu release http://www.ubuntu.com/getubuntu/download . Also, please be sure to provide any requested information that may have been missing. To reopen the bug, click on the current status under the Status column and change the status back to "New". Thanks.

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