[OB PATCH] Fix gdbserver build failure on targets without fork

Gary Benson
2016-01-18T11:44:43Z

Gary Benson wrote:
> Yao Qi wrote:
> > Function fork isn't available on uclinux target, so it causes
> > a compilation error like this below. Since my work touches
> > linux-bfin-low.c, I build GDBserver for bfin-uclinux, and the
> > error is found.
> [snip]
> > I don't know much about linux namespace stuff, so I didn't give
> > a fix here. Could you have a look?
>
> It probably needs a configure check, I'll add one.

Added.

---
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.
---
gdb/ChangeLog | 5 +
gdb/gdbserver/ChangeLog | 6 +
gdb/gdbserver/config.in | 21 +++
gdb/gdbserver/configure | 333 +++++++++++++++++++++++++++++++++++++-------
gdb/gdbserver/configure.ac | 1 +
gdb/nat/linux-namespaces.c | 15 ++-
6 files changed, 326 insertions(+), 55 deletions(-)

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
diff --git a/gdb/nat/linux-namespaces.c b/gdb/nat/linux-namespaces.c
index fb1467c..e9626ab 100644
--- a/gdb/nat/linux-namespaces.c
+++ b/gdb/nat/linux-namespaces.c
@@ -32,6 +32,19 @@
/* See nat/linux-namespaces.h. */
int debug_linux_namespaces;

+/* Handle systems without fork. */
+
+static inline pid_t
+do_fork (void)
+{
+#ifdef HAVE_FORK
+ return fork ();
+#else
+ errno = ENOSYS;
+ return -1;
+#endif
+}
+
/* Handle systems without setns. */

static inline int
@@ -644,7 +657,7 @@ linux_mntns_get_helper (void)
if (gdb_socketpair_cloexec (AF_UNIX, SOCK_STREAM, 0, sv) < 0)
return NULL;

- h.pid = fork ();
+ h.pid = do_fork ();
if (h.pid < 0)
{
int saved_errno = errno;
--
1.7.1