[patch] ON_STACK: Warn on buggy Linux i386 kernels
Marc Khouzam
marc.khouzam@ericsson.com
Sat Jul 21 02:58:00 GMT 2012
> ________________________________________
> From: Jan Kratochvil [jan.kratochvil@redhat.com]
> Sent: July 3, 2012 10:27 AM
> To: gdb-patches@sourceware.org
> Subject: [patch] ON_STACK: Warn on buggy Linux i386 kernels
>
> Hi,
>
> as discussed in:
> Possible future NX ON_STACk regression Re: [patch 3/3] Use ON_STACK for i386/amd64 (gdb2495.exp regression)
> http://sourceware.org/ml/gdb-patches/2012-06/msg00568.html
>
> I have found the problem with ON_STACK inferior calls affects only i386 Linux
> kernels (not x86_64, nor Fedora i386 PAE). It was fixed/removed in Fedora by
> commit 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd
> Author: Dave Jones <davej@redhat.com>
> Date: Mon Jun 4 11:56:08 2012 -0400
> disable 32bit nx, it seems to be broken
> http://pkgs.fedoraproject.org/gitweb/?p=kernel.git;a=commitdiff;h=88fa1f0332d188795ed73d7ac2b1564e11a0b4cd
> http://pkgs.fedoraproject.org/gitweb/?p=kernel.git;a=blob_plain;f=linux-2.6-32bit-mmap-exec-randomization.patch;hb=88fa1f0332d188795ed73d7ac2b1564e11a0b4cd
> http://pkgs.fedoraproject.org/gitweb/?p=kernel.git;a=blob_plain;f=linux-2.6-i386-nx-emulation.patch;hb=88fa1f0332d188795ed73d7ac2b1564e11a0b4cd
> http://pkgs.fedoraproject.org/gitweb/?p=kernel.git;a=blob_plain;f=nx-emu-remove-cpuinitdata-for-disable_nx-on-x86_32.patch;hb=88fa1f0332d188795ed73d7ac2b1564e11a0b4cd
> http://pkgs.fedoraproject.org/gitweb/?p=kernel.git;a=blob_plain;f=shlib_base_randomize.patch;hb=88fa1f0332d188795ed73d7ac2b1564e11a0b4cd
> So the last Fedora kernel where it was reproducible is: kernel-3.4.0-1.fc17.i686
>
> It does not seem to be ever present in upstream ("vanilla") Linux kernels.
>
> But I have found ubuntu-12.04-dvd-i386.iso (both GA and latest updates) which
> is LTS (=still maintained) is also affected by this problem so I expect there
> maybe vocal feedback.
That's me :) I'm seeing this warning. IIUC I can safely ignore this warning?
The warning is pretty intimidating:
(gdb) run
Starting program: myapp.exe
warning: Cannot call inferior functions, you have broken Linux kernel i386 NX (non-executable pages) support!
Thanks for having investigated this.
Marc
> It puts there only a warning. As it is both off-trunk patch and also the
> patch is present in neither old or new (at least Fedora) kernels and as it
> does not affect the most basic debugging I did not find it worth a workaround.
> Rather Ubuntu should provide a fix IMO.
>
>
> Thanks,
> Jan
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