corefiles not created in armhf chroot on arm64 porter

I was using the following version of gdb in both chroots:

GNU gdb (Ubuntu 7.11.90.20161005-0ubuntu1) 7.11.90.20161005-git

Manually running cat in gdb and executing the same commands as found in generate-sigsegv-crash.py had the following results:

(yakkety-armhf)brian@rugby:~$ gdb --args cat
GNU gdb (Ubuntu 7.11.90.20161005-0ubuntu1) 7.11.90.20161005-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from cat...(no debugging symbols found)...done.
(gdb) run
Starting program: /bin/cat
Cannot parse expression `.L954 4@r4'.
warning: Probes-based dynamic linker interface failed.
Reverting to original interface.

Program received signal SIGSEGV, Segmentation fault.
0xf772f9e4 in read () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) generate-core-file /tmp/my.core
Unable to fetch the floating point registers.: Invalid argument.

I thought this might be https://bugzilla.redhat.com/show_bug.cgi?id=1196181 but we seem to have the related patches in yakkety.

The issue also occurs in a zesty chroot:

brian@rugby:~$ schroot -c zesty-armhf
(zesty-armhf)brian@rugby:~$ sudo apt-get install screen
sudo: main: unable to allocate memory
(zesty-armhf)brian@rugby:~$ gdb
GNU gdb (Ubuntu 7.12-0ubuntu2) 7.12
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
(gdb) quit
(zesty-armhf)brian@rugby:~$ gdb --args cat
GNU gdb (Ubuntu 7.12-0ubuntu2) 7.12
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from cat...(no debugging symbols found)...done.
(gdb) run
Starting program: /bin/cat
Cannot parse expression `.L954 4@r4'.
warning: Probes-based dynamic linker interface failed.
Reverting to original interface.

^Z
Program received signal SIGTSTP, Stopped (user).
0xf7763b74 in read () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) generate-core-file /tmp/my.core
Unable to fetch the floating point registers.: Invalid argument.

ptrace(PTRACE_GETREGSET, 27642, NT_FPREGSET, 0xffcc67f0) = -1 EINVAL (Invalid argument)

NT_FPREGSET is "2", which the kernel calls NT_PRFPREG.

arm64 kernels don't implement this for compat processes, they only support NT_ARM_VFP. If I understand correctly, VFP is hard float, so it seems like this is a bug in gdb: it should only ask for NT_ARM_VFP, not NT_PRFPREG.

If I'm mistaken, then the kernel is missing support for compat tasks to issue NT_PRFPREG requests...

Kees provided me the following debdiffs for testing on zesty and yakkety armhf chroots.

I couldn't build the zesty debdiff on the arm64 porter box due to not being able to install the dependencies to build it. I did get the yakkety one to build and then extracted the package contents and used gdb from there. I was then able to create core files with this new gdb.

GNU gdb (Ubuntu 7.11.90.20161005-0ubuntu1.1) 7.11.90.20161005-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from cat...(no debugging symbols found)...done.
(gdb) Starting program: /bin/cat
Cannot parse expression `.L954 4@r4'.
warning: Probes-based dynamic linker interface failed.
Reverting to original interface.

Program received signal SIGSEGV, Segmentation fault.
0xf772f9e4 in read () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) Saved corefile /tmp/tmp8x5x1scn/my.core

I went so far as to run the generate-crashes script and it created core files for multiple applications.

This bug was fixed in the package gdb - 7.12-0ubuntu3

---------------
gdb (7.12-0ubuntu3) zesty; urgency=medium

  * Add debian/patches/armhf-fpregset.patch. LP: #1645501.

 -- Kees Cook <email address hidden> Tue, 29 Nov 2016 15:30:20 -0800

There is some discussion going on upstream regarding how to solve this, after that's sorted I'll redo the zesty patch and upload SRUs for this.

This was merged upstream:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=4bd2e1b2aee122b46e335d932f7833f9c86610d0

Hello Brian, or anyone else affected,

Accepted gdb into yakkety-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/gdb/7.11.90.20161005-0ubuntu2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Setting up gdb (7.11.90.20161005-0ubuntu2) ...
(yakkety-armhf)brian@rugby:~$ gdb --args cat
GNU gdb (Ubuntu 7.11.90.20161005-0ubuntu2) 7.11.90.20161005-git
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from cat...(no debugging symbols found)...done.
(gdb) run
Starting program: /bin/cat
Cannot parse expression `.L954 4@r4'.
warning: Probes-based dynamic linker interface failed.
Reverting to original interface.

^Z
Program received signal SIGTSTP, Stopped (user).
0xf772f9e4 in read () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) generate-core-file /tmp/my.core
Saved corefile /tmp/my.core

Setting to verification-done.

This bug was fixed in the package gdb - 7.11.90.20161005-0ubuntu2

---------------
gdb (7.11.90.20161005-0ubuntu2) yakkety; urgency=medium

  * Add debian/patches/armhf-fpregset.patch. LP: #1645501.

 -- Brian Murray <email address hidden> Wed, 18 Jan 2017 12:41:08 -0800

The verification of the Stable Release Update for gdb has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.