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Re: [Qemu-devel] [PATCH 2/2] linux-user: manage binfmt-misc preserve-arg
Re: [Qemu-devel] [PATCH 2/2] linux-user: manage binfmt-misc preserve-arg flag
Wed, 17 Jul 2019 12:07:09 +0200
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2
Le 14/07/2019 à 18:19, John Paul Adrian Glaubitz a écrit :
>> On Jul 14, 2019, at 3:40 PM, Laurent Vivier <address@hidden> wrote:
>> Add --preserve-arg0 in qemu-binfmt-conf.sh to configure the preserve-arg0
>> Now, if QEMU is started with -0 or QEMU_ARGV0 and an empty parameter
>> argv (the full pathname provided by binfmt-misc) is removed and
>> replaced by argv (the original argv provided by binfmt-misc when
>> 'P'/preserve-arg is set)
>> For instance:
>> $ sudo QEMU_ARGV0= chroot m68k-chroot sh -c 'echo $0'
>> without this patch:
>> $ sudo chroot m68k-chroot sh -c 'echo $0'
> As a regular user of qemu-user (we’re using qemu-user to run Debian’s buildds
> for m68k and sh4), I would like to add that the idea of having to pass
> additional environment variables to make qemu behave as expected, i.e. as the
> real hardware, is sub-optimal.
> I would prefer that enabling the preserve flag with the qemu-binfmt.sh script
> would make qemu-user behave correctly.
QEMU is not able to detect if it has been started by binfmt_misc with
the preserve-arg enabled or not, so it can't adapt the args analysis
to get the correct list.
> If I understand correctly, the current design with the environment variable
> was chosen because my preferred approach would break compatibility in certain
> cases. However, I think that correct emulation is more important than
> compatibility to an old broken behavior and I would therefore be in favor to
> make the correct behavior default.
> This will also be necessary when using qemu-user with Debian’s sbuild to
> “cross”-build packages with qemu-user. This particular bug was actually
> discovered while building Debian packages for m68k and sh4 using qemu-user.
The problem we have here is we don't know how qemu-user is used in the
wild. In my knowledge you are the most involved user, but you're not the
only one reporting problem via launchpad. Moreover, distros provide
qemu-user statically linked and binfmt configuration files, so we can
guess we have other users.
And I don't like to break existing things...
What I can propose:
1- modify this patch to add a configure option:
by default qemu will need the QEMU_ARGV0 but we will be able to
define at configure time it always runs with preserve-arg flag
enabled (something like "--enable-preserve-arg0")
[So debian will be able to provide qemu-user-static with this enabled by
default if you're not afraid to break debian users environment]
2- try (again) to push in the kernel the binfmt_misc namespace that
allows to have per chroot basis binfmt configuration
3- once 3 done, enable preserve-arg by default