Re: [Qemu-devel] [PATCH 2/2] linux-user: manage binfmt-misc preserve-arg[0] flag

[John Paul Adrian Glaubitz]

Hi!

> 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
> flag.
> 
> Now, if QEMU is started with -0 or QEMU_ARGV0 and an empty parameter
> argv[0] (the full pathname provided by binfmt-misc) is removed and
> replaced by argv[1] (the original argv[0] provided by binfmt-misc when
> 'P'/preserve-arg[0] is set)
> 
> For instance:
> 
>  $ sudo QEMU_ARGV0= chroot m68k-chroot sh -c 'echo $0'
>  sh
> 
> without this patch:
> 
>  $ sudo chroot m68k-chroot sh -c 'echo $0'
>  /usr/bin/sh

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.

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.

Thanks,
Adrian

PS: I have disabled receiving messages for this list, so please keep me CC’ed.