[patch] fix tkill_failed gcc warning in gdbserver

[dje@google.com (Doug Evans)]

Hi.

android doesn't have SYS_tkill but it does have __NR_tkill.

I will check this in tomorrow, pending objections.

This includes some minor tweaking to linux-nat.c:kill_lwp.
The code changes are technically better, and I like the consistency.

2009-12-21  Doug Evans  <dje@google.com>

	gdb/
	* linux-nat.c (kill_lwp): Minor cleanup, move definition of
	tkill_failed into ifdef HAVE_TKILL_SYSCALL.  Move setting of errno
	there too.  Delete unnecessary resetting of errno after syscall.
	Minor comment changes to match gdbserver/linux-low.c:kill_lwp.

	gdbserver/
	* configure.ac: Look for both __NR_tkill and SYS_tkill.
	Define TKILL_SYSCALL_NAME to the one we find, if any.
	* config.in: Regenerate.
	* configure: Regenerate.
	* linux-low.c (kill_lwp): Move definition of tkill_failed to
	ifdef TKILL_SYSCALL_NAME to avoid gcc warning.  Move setting of errno
	there too.  Delete unnecessary resetting of errno after syscall.
	Minor comment changes to match gdb/linux-nat.c:kill_lwp.

Index: linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-nat.c,v
retrieving revision 1.156
diff -u -p -r1.156 linux-nat.c
--- linux-nat.c	20 Nov 2009 19:48:45 -0000	1.156
+++ linux-nat.c	21 Dec 2009 19:43:51 -0000
@@ -2034,27 +2034,29 @@ linux_nat_resume (struct target_ops *ops
     target_async (inferior_event_handler, 0);
 }
 
-/* Issue kill to specified lwp.  */
-
-static int tkill_failed;
+/* Send a signal to an LWP.  */
 
 static int
 kill_lwp (int lwpid, int signo)
 {
-  errno = 0;
-
-/* Use tkill, if possible, in case we are using nptl threads.  If tkill
-   fails, then we are not using nptl threads and we should be using kill.  */
+  /* Use tkill, if possible, in case we are using nptl threads.  If tkill
+     fails, then we are not using nptl threads and we should be using kill.  */
 
 #ifdef HAVE_TKILL_SYSCALL
-  if (!tkill_failed)
-    {
-      int ret = syscall (__NR_tkill, lwpid, signo);
-      if (errno != ENOSYS)
-	return ret;
-      errno = 0;
-      tkill_failed = 1;
-    }
+  {
+    static int tkill_failed;
+
+    if (!tkill_failed)
+      {
+	int ret;
+
+	errno = 0;
+	ret = syscall (__NR_tkill, lwpid, signo);
+	if (errno != ENOSYS)
+	  return ret;
+	tkill_failed = 1;
+      }
+  }
 #endif
 
   return kill (lwpid, signo);
Index: gdbserver/configure.ac
===================================================================
RCS file: /cvs/src/src/gdb/gdbserver/configure.ac,v
retrieving revision 1.30
diff -u -p -r1.30 configure.ac
--- gdbserver/configure.ac	17 Nov 2009 17:58:15 -0000	1.30
+++ gdbserver/configure.ac	21 Dec 2009 19:43:51 -0000
@@ -1,5 +1,5 @@
 dnl Autoconf configure script for GDB server.
-dnl Copyright (C) 2000, 2002, 2003, 2004, 2005, 2006, 2007, 2008
+dnl Copyright (C) 2000, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
 dnl Free Software Foundation, Inc.
 dnl
 dnl This file is part of GDB.
@@ -196,6 +205,34 @@ AS_HELP_STRING([--with-libthread-db=PATH
   srv_libs="$srv_libthread_db_path"
 ])
 
+dnl See if sys/syscall.h has __NR_tkill or SYS_tkill.
+AC_CACHE_CHECK([whether <sys/syscall.h> has __NR_tkill],
+               gdb_cv_sys_syscall_h_has_NR_tkill,
+  AC_TRY_COMPILE(
+    [#include <sys/syscall.h>],
+    [int i = __NR_tkill;],
+    gdb_cv_sys_syscall_h_has_NR_tkill=yes,
+    gdb_cv_sys_syscall_h_has_NR_tkill=no
+  )
+)
+if test "x$gdb_cv_sys_syscall_h_has_NR_tkill" != "xyes"; then
+  AC_CACHE_CHECK([whether <sys/syscall.h> has __SYS_tkill],
+                  gdb_cv_sys_syscall_h_has_SYS_tkill,
+    AC_TRY_COMPILE(
+      [#include <sys/syscall.h>],
+      [int i = SYS_tkill;],
+      gdb_cv_sys_syscall_h_has_SYS_tkill=yes,
+      gdb_cv_sys_syscall_h_has_SYS_tkill=no
+    )
+  )
+fi
+dnl See if we can issue tkill syscall.
+if test "x$gdb_cv_sys_syscall_h_has_NR_tkill" = "xyes"; then
+  AC_DEFINE(TKILL_SYSCALL_NAME, __NR_tkill, [Name of the tkill syscall.])
+elif test "x$gdb_cv_sys_syscall_h_has_SYS_tkill" = "xyes"; then
+  AC_DEFINE(TKILL_SYSCALL_NAME, SYS_tkill, [Name of the tkill syscall.])
+fi
+
 if test "$srv_xmlfiles" != ""; then
   srv_xmlbuiltin="xml-builtin.o"
   AC_DEFINE(USE_XML, 1, [Define if an XML target description is available.])
Index: gdbserver/linux-low.c
===================================================================
RCS file: /cvs/src/src/gdb/gdbserver/linux-low.c,v
retrieving revision 1.117
diff -u -p -r1.117 linux-low.c
--- gdbserver/linux-low.c	21 Dec 2009 17:54:03 -0000	1.117
+++ gdbserver/linux-low.c	21 Dec 2009 19:43:51 -0000
@@ -1572,25 +1572,29 @@ linux_wait (ptid_t ptid,
   return event_ptid;
 }
 
-/* Send a signal to an LWP.  For LinuxThreads, kill is enough; however, if
-   thread groups are in use, we need to use tkill.  */
+/* Send a signal to an LWP.  */
 
 static int
 kill_lwp (unsigned long lwpid, int signo)
 {
-  static int tkill_failed;
+  /* Use tkill, if possible, in case we are using nptl threads.  If tkill
+     fails, then we are not using nptl threads and we should be using kill.  */
 
-  errno = 0;
-
-#ifdef SYS_tkill
-  if (!tkill_failed)
-    {
-      int ret = syscall (SYS_tkill, lwpid, signo);
-      if (errno != ENOSYS)
-	return ret;
-      errno = 0;
-      tkill_failed = 1;
-    }
+#ifdef TKILL_SYSCALL_NAME
+  {
+    static int tkill_failed;
+
+    if (!tkill_failed)
+      {
+	int ret;
+
+	errno = 0;
+	ret = syscall (TKILL_SYSCALL_NAME, lwpid, signo);
+	if (errno != ENOSYS)
+	  return ret;
+	tkill_failed = 1;
+      }
+  }
 #endif
 
   return kill (lwpid, signo);