Re: [Qemu-devel] [PATCH v2 2/2] linux-user: manage binfmt-misc preserve-arg[0] flag

[Christophe de Dinechin <dinechin@redhat.com>]

Laurent Vivier writes:

> Add --preserve-arg0 in qemu-binfmt-conf.sh to configure the preserve-arg0
> flag.

There is an inconsistency below, where some parts use preserve-argv0
and others preserve-arg0 (no v)

Frankly, I would accept both ;-)

>
> 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
>
> QEMU can be forced to always use preserve-argv[0] at configuration
> time with --force-preserve-argv0

Example of 'argv0' case

>
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
>
> Notes:
>     v2: add --force-preserve-argv0 configure option
>
>  configure                   |  8 +++++++
>  linux-user/main.c           | 24 +++++++++++++++++++-
>  scripts/qemu-binfmt-conf.sh | 44 +++++++++++++++++++++++--------------
>  3 files changed, 58 insertions(+), 18 deletions(-)
>
> diff --git a/configure b/configure
> index 95134c0180b2..3568e192776c 100755
> --- a/configure
> +++ b/configure
> @@ -498,6 +498,7 @@ libxml2=""
>  docker="no"
>  debug_mutex="no"
>  libpmem=""
> +force_preserve_argv0="no"
>  default_devices="yes"
>
>  # cross compilers defaults, can be overridden with --cross-cc-ARCH
> @@ -1543,6 +1544,8 @@ for opt do
>    ;;
>    --disable-libpmem) libpmem=no
>    ;;
> +  --force-preserve-argv0) force_preserve_argv0=yes
> +  ;;
>    *)
>        echo "ERROR: unknown option $opt"
>        echo "Try '$0 --help' for more information"
> @@ -1740,6 +1743,8 @@ Advanced options (experts only):
>    --enable-profiler        profiler support
>    --enable-debug-stack-usage
>                             track the maximum stack usage of stacks created by qemu_alloc_stack
> +  --force-preserve-argv0   for linux-user only, force the use of binfmt_misc 'P'
> +                           flag (preserve-argv[0])
>
>  Optional features, enabled with --enable-FEATURE and
>  disabled with --disable-FEATURE, default is enabled if available:
> @@ -7736,6 +7741,9 @@ if test "$target_user_only" = "yes" ; then
>  fi
>  if test "$target_linux_user" = "yes" ; then
>    echo "CONFIG_LINUX_USER=y" >> $config_target_mak
> +  if test "$force_preserve_argv0" = "yes" ; then
> +    echo "CONFIG_FORCE_PRESERVE_ARGV0=y" >> $config_target_mak
> +  fi
>  fi
>  list=""
>  if test ! -z "$gdb_xml_files" ; then
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 28f0065b6ddf..02354d58e866 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -605,6 +605,7 @@ int main(int argc, char **argv, char **envp)
>      int i;
>      int ret;
>      int execfd;
> +    bool preserve_argv0;
>
>      error_init(argv[0]);
>      module_call_init(MODULE_INIT_TRACE);
> @@ -653,6 +654,9 @@ int main(int argc, char **argv, char **envp)
>
>      init_qemu_uname_release();
>
> +    /*
> +     * Manage binfmt-misc open-binary flag
> +     */
>      execfd = qemu_getauxval(AT_EXECFD);
>      if (execfd == 0) {
>          execfd = open(exec_path, O_RDONLY);
> @@ -662,6 +666,24 @@ int main(int argc, char **argv, char **envp)
>          }
>      }
>
> +     /*
> +      * argv0 with an empty string will set argv[optind + 1]
> +      * as target_argv[0]
> +      */
> +#ifdef CONFIG_FORCE_PRESERVE_ARGV0
> +    preserve_argv0 = true;
> +#else
> +    preserve_argv0 = (argv0 != NULL && argv0[0] == 0);
> +#endif
> +    /*
> +     * Manage binfmt-misc preserve-arg[0] flag
> +     *    argv[optind]     full path to the binary
> +     *    argv[optind + 1] original argv[0]
> +     */
> +    if (optind + 1 < argc && preserve_argv0) {
> +        optind++;
> +    }
> +
>      if (cpu_model == NULL) {
>          cpu_model = cpu_get_model(get_elf_eflags(execfd));
>      }
> @@ -766,7 +788,7 @@ int main(int argc, char **argv, char **envp)
>       * argv[0] pointer with the given one.
>       */
>      i = 0;
> -    if (argv0 != NULL) {
> +    if (argv0 != NULL && argv0[0] != 0) {
>          target_argv[i++] = strdup(argv0);
>      }
>      for (; i < target_argc; i++) {
> diff --git a/scripts/qemu-binfmt-conf.sh b/scripts/qemu-binfmt-conf.sh
> index b5a16742a149..7c9a4609c232 100755
> --- a/scripts/qemu-binfmt-conf.sh
> +++ b/scripts/qemu-binfmt-conf.sh
> @@ -170,25 +170,27 @@ usage() {
>  Usage: qemu-binfmt-conf.sh [--qemu-path PATH][--debian][--systemd CPU]
>                             [--help][--credential yes|no][--exportdir PATH]
>                             [--persistent yes|no][--qemu-suffix SUFFIX]
> +                           [--preserve-arg0 yes|no]

Example of arg0 case

>
>         Configure binfmt_misc to use qemu interpreter
>
> -       --help:        display this usage
> -       --qemu-path:   set path to qemu interpreter ($QEMU_PATH)
> -       --qemu-suffix: add a suffix to the default interpreter name
> -       --debian:      don't write into /proc,
> -                      instead generate update-binfmts templates
> -       --systemd:     don't write into /proc,
> -                      instead generate file for systemd-binfmt.service
> -                      for the given CPU. If CPU is "ALL", generate a
> -                      file for all known cpus
> -       --exportdir:   define where to write configuration files
> -                      (default: $SYSTEMDDIR or $DEBIANDIR)
> -       --credential:  if yes, credential and security tokens are
> -                      calculated according to the binary to interpret
> -       --persistent:  if yes, the interpreter is loaded when binfmt is
> -                      configured and remains in memory. All future uses
> -                      are cloned from the open file.
> +       --help:          display this usage
> +       --qemu-path:     set path to qemu interpreter ($QEMU_PATH)
> +       --qemu-suffix:   add a suffix to the default interpreter name
> +       --debian:        don't write into /proc,
> +                        instead generate update-binfmts templates
> +       --systemd:       don't write into /proc,
> +                        instead generate file for systemd-binfmt.service
> +                        for the given CPU. If CPU is "ALL", generate a
> +                        file for all known cpus
> +       --exportdir:     define where to write configuration files
> +                        (default: $SYSTEMDDIR or $DEBIANDIR)
> +       --credential:    if yes, credential and security tokens are
> +                        calculated according to the binary to interpret
> +       --persistent:    if yes, the interpreter is loaded when binfmt is
> +                        configured and remains in memory. All future uses
> +                        are cloned from the open file.
> +       --preserve-arg0  preserve arg[0]
>
>      To import templates with update-binfmts, use :
>
> @@ -261,6 +263,9 @@ qemu_generate_register() {
>      if [ "$PERSISTENT" = "yes" ] ; then
>          flags="${flags}F"
>      fi
> +    if [ "$PRESERVE_ARG0" = "yes" ] ; then
> +        flags="${flags}P"
> +    fi
>
>      echo ":qemu-$cpu:M::$magic:$mask:$qemu:$flags"
>  }
> @@ -322,9 +327,10 @@ DEBIANDIR="/usr/share/binfmts"
>  QEMU_PATH=/usr/local/bin
>  CREDENTIAL=no
>  PERSISTENT=no
> +PRESERVE_ARG0=no
>  QEMU_SUFFIX=""
>
> -options=$(getopt -o ds:Q:S:e:hc:p: -l debian,systemd:,qemu-path:,qemu-suffix:,exportdir:,help,credential:,persistent: -- "$@")
> +options=$(getopt -o ds:Q:S:e:hc:p:0: -l debian,systemd:,qemu-path:,qemu-suffix:,exportdir:,help,credential:,persistent:,preserve-arg0: -- "$@")
>  eval set -- "$options"
>
>  while true ; do
> @@ -380,6 +386,10 @@ while true ; do
>          shift
>          PERSISTENT="$1"
>          ;;
> +    -0|--preserve-arg0)
> +        shift
> +        PRESERVE_ARG0="$1"
> +        ;;
>      *)
>          break
>          ;;


--
Cheers,
Christophe de Dinechin (IRC c3d)