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


From: Laurent Vivier
Subject: [Qemu-devel] [PATCH 2/2] linux-user: manage binfmt-misc preserve-arg[0] flag
Date: Sun, 14 Jul 2019 15:40:28 +0200

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

Signed-off-by: Laurent Vivier <address@hidden>
---
 linux-user/main.c           | 18 ++++++++++++++-
 scripts/qemu-binfmt-conf.sh | 44 +++++++++++++++++++++++--------------
 2 files changed, 44 insertions(+), 18 deletions(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index ef8e8cb10eba..eeaba4a7b914 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -647,6 +647,9 @@ 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);
@@ -656,6 +659,19 @@ int main(int argc, char **argv, char **envp)
         }
     }
 
+    /*
+     * Manage binfmt-misc preserve-arg[0] flag
+     *    argv[optind]     full path to the binary
+     *    argv[optind + 1] original argv[0]
+     */
+    if (optind + 1 < argc && argv0 != NULL && argv0[0] == 0) {
+        /*
+         * argv0 with an empty string will set argv[optind + 1]
+         * as target_argv[0]
+         */
+        optind++;
+    }
+
     if (cpu_model == NULL) {
         cpu_model = cpu_get_model(get_elf_eflags(execfd));
     }
@@ -760,7 +776,7 @@ 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]
 
        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
         ;;
-- 
2.21.0




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