Fix gdbserver build failure on targets without fork

This commit fixes nat/linux-namespaces.c to build correctly on
targets without fork.

gdb/ChangeLog:

	* nat/linux-namespaces.c (do_fork): New function.
	(linux_mntns_get_helper): Use the above.

gdb/gdbserver/ChangeLog:

	* configure.ac (AC_FUNC_FORK): New check.
	* config.in: Regenerate.
	* configure: Likewise.

4 files changed, 307 insertions, 54 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index a76bb14..2311d03 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,9 @@
+2016-01-18  Gary Benson  <gbenson@redhat.com>
+
+	* configure.ac (AC_FUNC_FORK): New check.
+	* config.in: Regenerate.
+	* configure: Likewise.
+
 2016-01-14  Yao Qi  <yao.qi@linaro.org>
 
 	* linux-aarch32-low.c (thumb2_breakpoint): Make it static.
diff --git a/gdb/gdbserver/config.in b/gdb/gdbserver/config.in
index e2566a9..2c3a69a 100644
--- a/gdb/gdbserver/config.in
+++ b/gdb/gdbserver/config.in
@@ -99,6 +99,9 @@
 /* Define to 1 if you have the `fdwalk' function. */
 #undef HAVE_FDWALK
 
+/* Define to 1 if you have the `fork' function. */
+#undef HAVE_FORK
+
 /* Define to 1 if you have the `getauxval' function. */
 #undef HAVE_GETAUXVAL
 
@@ -286,9 +289,21 @@
 /* Define if UST is available */
 #undef HAVE_UST
 
+/* Define to 1 if you have the `vfork' function. */
+#undef HAVE_VFORK
+
+/* Define to 1 if you have the <vfork.h> header file. */
+#undef HAVE_VFORK_H
+
 /* Define to 1 if you have the <wait.h> header file. */
 #undef HAVE_WAIT_H
 
+/* Define to 1 if `fork' works. */
+#undef HAVE_WORKING_FORK
+
+/* Define to 1 if `vfork' works. */
+#undef HAVE_WORKING_VFORK
+
 /* Define to the address where bug reports for this package should be sent. */
 #undef PACKAGE_BUGREPORT
 
@@ -393,3 +408,9 @@
 
 /* Define to 1 if you need to in order for `stat' and other things to work. */
 #undef _POSIX_SOURCE
+
+/* Define to `int' if <sys/types.h> does not define. */
+#undef pid_t
+
+/* Define as `fork' if `vfork' does not work. */
+#undef vfork
diff --git a/gdb/gdbserver/configure b/gdb/gdbserver/configure
index 57af951..763c77d 100755
--- a/gdb/gdbserver/configure
+++ b/gdb/gdbserver/configure
@@ -1772,6 +1772,60 @@ fi
 
 } # ac_fn_c_try_link
 
+# ac_fn_c_check_type LINENO TYPE VAR INCLUDES
+# -------------------------------------------
+# Tests whether TYPE exists after having included INCLUDES, setting cache
+# variable VAR accordingly.
+ac_fn_c_check_type ()
+{
+  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2" >&5
+$as_echo_n "checking for $2... " >&6; }
+if { as_var=$3; eval "test \"\${$as_var+set}\" = set"; }; then :
+  $as_echo_n "(cached) " >&6
+else
+  eval "$3=no"
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+$4
+int
+main ()
+{
+if (sizeof ($2))
+	 return 0;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+$4
+int
+main ()
+{
+if (sizeof (($2)))
+	    return 0;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+else
+  eval "$3=yes"
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+eval ac_res=\$$3
+	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+  eval $as_lineno_stack; test "x$as_lineno_stack" = x && { as_lineno=; unset as_lineno;}
+
+} # ac_fn_c_check_type
+
 # ac_fn_c_check_func LINENO FUNC VAR
 # ----------------------------------
 # Tests whether FUNC exists, setting the cache variable VAR accordingly
@@ -1929,60 +1983,6 @@ $as_echo "$ac_res" >&6; }
 
 } # ac_fn_cxx_check_decl
 
-# ac_fn_c_check_type LINENO TYPE VAR INCLUDES
-# -------------------------------------------
-# Tests whether TYPE exists after having included INCLUDES, setting cache
-# variable VAR accordingly.
-ac_fn_c_check_type ()
-{
-  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2" >&5
-$as_echo_n "checking for $2... " >&6; }
-if { as_var=$3; eval "test \"\${$as_var+set}\" = set"; }; then :
-  $as_echo_n "(cached) " >&6
-else
-  eval "$3=no"
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-$4
-int
-main ()
-{
-if (sizeof ($2))
-	 return 0;
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-$4
-int
-main ()
-{
-if (sizeof (($2)))
-	    return 0;
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-
-else
-  eval "$3=yes"
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-fi
-eval ac_res=\$$3
-	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
-$as_echo "$ac_res" >&6; }
-  eval $as_lineno_stack; test "x$as_lineno_stack" = x && { as_lineno=; unset as_lineno;}
-
-} # ac_fn_c_check_type
-
 # ac_fn_c_compute_int LINENO EXPR VAR INCLUDES
 # --------------------------------------------
 # Tries to find the compile-time value of EXPR in a program that includes
@@ -5360,6 +5360,231 @@ fi
 
 done
 
+ac_fn_c_check_type "$LINENO" "pid_t" "ac_cv_type_pid_t" "$ac_includes_default"
+if test "x$ac_cv_type_pid_t" = x""yes; then :
+
+else
+
+cat >>confdefs.h <<_ACEOF
+#define pid_t int
+_ACEOF
+
+fi
+
+for ac_header in vfork.h
+do :
+  ac_fn_c_check_header_mongrel "$LINENO" "vfork.h" "ac_cv_header_vfork_h" "$ac_includes_default"
+if test "x$ac_cv_header_vfork_h" = x""yes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_VFORK_H 1
+_ACEOF
+
+fi
+
+done
+
+for ac_func in fork vfork
+do :
+  as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
+ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
+eval as_val=\$$as_ac_var
+   if test "x$as_val" = x""yes; then :
+  cat >>confdefs.h <<_ACEOF
+#define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
+_ACEOF
+
+fi
+done
+
+if test "x$ac_cv_func_fork" = xyes; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for working fork" >&5
+$as_echo_n "checking for working fork... " >&6; }
+if test "${ac_cv_func_fork_works+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test "$cross_compiling" = yes; then :
+  ac_cv_func_fork_works=cross
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+$ac_includes_default
+int
+main ()
+{
+
+	  /* By Ruediger Kuhlmann. */
+	  return fork () < 0;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_run "$LINENO"; then :
+  ac_cv_func_fork_works=yes
+else
+  ac_cv_func_fork_works=no
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
+  conftest.$ac_objext conftest.beam conftest.$ac_ext
+fi
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_func_fork_works" >&5
+$as_echo "$ac_cv_func_fork_works" >&6; }
+
+else
+  ac_cv_func_fork_works=$ac_cv_func_fork
+fi
+if test "x$ac_cv_func_fork_works" = xcross; then
+  case $host in
+    *-*-amigaos* | *-*-msdosdjgpp*)
+      # Override, as these systems have only a dummy fork() stub
+      ac_cv_func_fork_works=no
+      ;;
+    *)
+      ac_cv_func_fork_works=yes
+      ;;
+  esac
+  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: result $ac_cv_func_fork_works guessed because of cross compilation" >&5
+$as_echo "$as_me: WARNING: result $ac_cv_func_fork_works guessed because of cross compilation" >&2;}
+fi
+ac_cv_func_vfork_works=$ac_cv_func_vfork
+if test "x$ac_cv_func_vfork" = xyes; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for working vfork" >&5
+$as_echo_n "checking for working vfork... " >&6; }
+if test "${ac_cv_func_vfork_works+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test "$cross_compiling" = yes; then :
+  ac_cv_func_vfork_works=cross
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+/* Thanks to Paul Eggert for this test.  */
+$ac_includes_default
+#include <sys/wait.h>
+#ifdef HAVE_VFORK_H
+# include <vfork.h>
+#endif
+/* On some sparc systems, changes by the child to local and incoming
+   argument registers are propagated back to the parent.  The compiler
+   is told about this with #include <vfork.h>, but some compilers
+   (e.g. gcc -O) don't grok <vfork.h>.  Test for this by using a
+   static variable whose address is put into a register that is
+   clobbered by the vfork.  */
+static void
+#ifdef __cplusplus
+sparc_address_test (int arg)
+# else
+sparc_address_test (arg) int arg;
+#endif
+{
+  static pid_t child;
+  if (!child) {
+    child = vfork ();
+    if (child < 0) {
+      perror ("vfork");
+      _exit(2);
+    }
+    if (!child) {
+      arg = getpid();
+      write(-1, "", 0);
+      _exit (arg);
+    }
+  }
+}
+
+int
+main ()
+{
+  pid_t parent = getpid ();
+  pid_t child;
+
+  sparc_address_test (0);
+
+  child = vfork ();
+
+  if (child == 0) {
+    /* Here is another test for sparc vfork register problems.  This
+       test uses lots of local variables, at least as many local
+       variables as main has allocated so far including compiler
+       temporaries.  4 locals are enough for gcc 1.40.3 on a Solaris
+       4.1.3 sparc, but we use 8 to be safe.  A buggy compiler should
+       reuse the register of parent for one of the local variables,
+       since it will think that parent can't possibly be used any more
+       in this routine.  Assigning to the local variable will thus
+       munge parent in the parent process.  */
+    pid_t
+      p = getpid(), p1 = getpid(), p2 = getpid(), p3 = getpid(),
+      p4 = getpid(), p5 = getpid(), p6 = getpid(), p7 = getpid();
+    /* Convince the compiler that p..p7 are live; otherwise, it might
+       use the same hardware register for all 8 local variables.  */
+    if (p != p1 || p != p2 || p != p3 || p != p4
+	|| p != p5 || p != p6 || p != p7)
+      _exit(1);
+
+    /* On some systems (e.g. IRIX 3.3), vfork doesn't separate parent
+       from child file descriptors.  If the child closes a descriptor
+       before it execs or exits, this munges the parent's descriptor
+       as well.  Test for this by closing stdout in the child.  */
+    _exit(close(fileno(stdout)) != 0);
+  } else {
+    int status;
+    struct stat st;
+
+    while (wait(&status) != child)
+      ;
+    return (
+	 /* Was there some problem with vforking?  */
+	 child < 0
+
+	 /* Did the child fail?  (This shouldn't happen.)  */
+	 || status
+
+	 /* Did the vfork/compiler bug occur?  */
+	 || parent != getpid()
+
+	 /* Did the file descriptor bug occur?  */
+	 || fstat(fileno(stdout), &st) != 0
+	 );
+  }
+}
+_ACEOF
+if ac_fn_c_try_run "$LINENO"; then :
+  ac_cv_func_vfork_works=yes
+else
+  ac_cv_func_vfork_works=no
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
+  conftest.$ac_objext conftest.beam conftest.$ac_ext
+fi
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_func_vfork_works" >&5
+$as_echo "$ac_cv_func_vfork_works" >&6; }
+
+fi;
+if test "x$ac_cv_func_fork_works" = xcross; then
+  ac_cv_func_vfork_works=$ac_cv_func_vfork
+  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: result $ac_cv_func_vfork_works guessed because of cross compilation" >&5
+$as_echo "$as_me: WARNING: result $ac_cv_func_vfork_works guessed because of cross compilation" >&2;}
+fi
+
+if test "x$ac_cv_func_vfork_works" = xyes; then
+
+$as_echo "#define HAVE_WORKING_VFORK 1" >>confdefs.h
+
+else
+
+$as_echo "#define vfork fork" >>confdefs.h
+
+fi
+if test "x$ac_cv_func_fork_works" = xyes; then
+
+$as_echo "#define HAVE_WORKING_FORK 1" >>confdefs.h
+
+fi
+
 for ac_func in getauxval pread pwrite pread64 setns
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
diff --git a/gdb/gdbserver/configure.ac b/gdb/gdbserver/configure.ac
index 8476fbd..f15ee1f 100644
--- a/gdb/gdbserver/configure.ac
+++ b/gdb/gdbserver/configure.ac
@@ -94,6 +94,7 @@ AC_CHECK_HEADERS(sgtty.h termio.h termios.h sys/reg.h string.h dnl
 		 fcntl.h signal.h sys/file.h dnl
 		 sys/ioctl.h netinet/in.h sys/socket.h netdb.h dnl
 		 netinet/tcp.h arpa/inet.h)
+AC_FUNC_FORK
 AC_CHECK_FUNCS(getauxval pread pwrite pread64 setns)
 
 GDB_AC_COMMON