Le 08/12/2020 à 17:04, Matteo Croce a écrit : > On Tue, Dec 8, 2020 at 9:21 AM Laurent Vivier <laur...@vivier.eu> wrote: >> >> Le 08/12/2020 à 01:17, Matteo Croce a écrit : >>> From: Matteo Croce <mcr...@microsoft.com> >>> >>> Add a '-c' option which does a chroot() just before starting the >>> emulation. This is useful when the static QEMU user binary can't >>> be copied into the target root filesystem, e.g. if it's readonly. >> >> Did you try to use the binfmt_misc 'F' flag (fix binary)? >> >> https://www.kernel.org/doc/Documentation/admin-guide/binfmt-misc.rst >> >> ``F`` - fix binary >> >> The usual behaviour of binfmt_misc is to spawn the >> binary lazily when the misc format file is invoked. However, >> this doesn``t work very well in the face of mount namespaces and >> changeroots, so the ``F`` mode opens the binary as soon as the >> emulation is installed and uses the opened image to spawn the >> emulator, meaning it is always available once installed, >> regardless of how the environment changes. >> >> This can be configured with scripts/qemu-binfmt-conf.sh and >> "--persistent yes"" option >> > > Yes, this works too. > Basically it's the same trick, open the binary early and then emulate. > The only difference is that with binfmt emulation the procfs open > still fails: > > # strace -feopenat chroot debian /bin/true 2>&1 |grep /proc/sys > [pid 9359] openat(AT_FDCWD, "/proc/sys/vm/mmap_min_addr", O_RDONLY) = > -1 ENOENT (No such file or directory) > > vs > > # strace -feopenat qemu-aarch64 -c debian /bin/true 2>&1 |grep /proc/sys > [pid 9348] openat(AT_FDCWD, "/proc/sys/vm/mmap_min_addr", O_RDONLY) = 3 >
If you want to have the /proc mounted earlier you can use "unshare". something like: unshare --mount-proc -R debian /bin/true There is also the "-L" option, something like: qemu-aarch64 -L debian debian/bin/true Thanks, Laurent
