Fix gdbserver --debug issues caught by Valgrind

Running gdbserver --debug under Valgrind shows:

 ==4803== Invalid read of size 4
 ==4803==    at 0x432B62: linux_write_memory (linux-low.c:5320)
 ==4803==    by 0x4143F7: write_inferior_memory (target.c:83)
 ==4803==    by 0x415895: remove_memory_breakpoint (mem-break.c:362)
 ==4803==    by 0x432EF5: linux_remove_point (linux-low.c:5460)
 ==4803==    by 0x416319: delete_raw_breakpoint (mem-break.c:802)
 ==4803==    by 0x4163F3: release_breakpoint (mem-break.c:842)
 ==4803==    by 0x416477: delete_breakpoint_1 (mem-break.c:869)
 ==4803==    by 0x4164EF: delete_breakpoint (mem-break.c:891)
 ==4803==    by 0x416843: delete_gdb_breakpoint_1 (mem-break.c:1069)
 ==4803==    by 0x4168D8: delete_gdb_breakpoint (mem-break.c:1098)
 ==4803==    by 0x4134E3: process_serial_event (server.c:4051)
 ==4803==    by 0x4138E4: handle_serial_event (server.c:4196)
 ==4803==  Address 0x4c6b930 is 0 bytes inside a block of size 1 alloc'd
 ==4803==    at 0x4A0645D: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
 ==4803==    by 0x4240C6: xmalloc (common-utils.c:43)
 ==4803==    by 0x41439C: write_inferior_memory (target.c:80)
 ==4803==    by 0x415895: remove_memory_breakpoint (mem-break.c:362)
 ==4803==    by 0x432EF5: linux_remove_point (linux-low.c:5460)
 ==4803==    by 0x416319: delete_raw_breakpoint (mem-break.c:802)
 ==4803==    by 0x4163F3: release_breakpoint (mem-break.c:842)
 ==4803==    by 0x416477: delete_breakpoint_1 (mem-break.c:869)
 ==4803==    by 0x4164EF: delete_breakpoint (mem-break.c:891)
 ==4803==    by 0x416843: delete_gdb_breakpoint_1 (mem-break.c:1069)
 ==4803==    by 0x4168D8: delete_gdb_breakpoint (mem-break.c:1098)
 ==4803==    by 0x4134E3: process_serial_event (server.c:4051)
 ==4803==

And:

 ==7272== Conditional jump or move depends on uninitialised value(s)
 ==7272==    at 0x3615E48361: vfprintf (vfprintf.c:1634)
 ==7272==    by 0x414E89: debug_vprintf (debug.c:60)
 ==7272==    by 0x42800A: debug_printf (common-debug.c:35)
 ==7272==    by 0x43937B: my_waitpid (linux-waitpid.c:149)
 ==7272==    by 0x42D740: linux_wait_for_event_filtered (linux-low.c:2441)
 ==7272==    by 0x42DADA: linux_wait_for_event (linux-low.c:2552)
 ==7272==    by 0x42E165: linux_wait_1 (linux-low.c:2860)
 ==7272==    by 0x42F5D8: linux_wait (linux-low.c:3453)
 ==7272==    by 0x4144A4: mywait (target.c:107)
 ==7272==    by 0x413969: handle_target_event (server.c:4214)
 ==7272==    by 0x41A1A6: handle_file_event (event-loop.c:429)
 ==7272==    by 0x41996D: process_event (event-loop.c:184)

gdb/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* nat/linux-waitpid.c (my_waitpid): Only print *status if waitpid
	returned > 0.

gdb/gdbserver/ChangeLog:
2015-08-06  Pedro Alves  <palves@redhat.com>

	* linux-low.c (linux_write_memory): Rewrite debug output to avoid
	reading beyond the passed in buffer length.

4 files changed, 24 insertions, 10 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 591fe25..193581f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-06  Pedro Alves  <palves@redhat.com>
+
+	* nat/linux-waitpid.c (my_waitpid): Only print *status if waitpid
+	returned > 0.
+
 2015-08-06  Pierre Langlois  <pierre.langlois@arm.com>
 
 	* common/agent.c (symbol_list) <required>: Remove.
diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index e45050a..79904d9 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-06  Pedro Alves  <palves@redhat.com>
+
+	* linux-low.c (linux_write_memory): Rewrite debug output to avoid
+	reading beyond the passed in buffer length.
+
 2015-08-06  Pierre Langlois  <pierre.langlois@arm.com>
 
 	* tracepoint.c (symbol_list) <required>: Remove.
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 98fffc9..2146a2c 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5336,15 +5336,19 @@ linux_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len)
   if (debug_threads)
     {
       /* Dump up to four bytes.  */
-      unsigned int val = * (unsigned int *) myaddr;
-      if (len == 1)
-	val = val & 0xff;
-      else if (len == 2)
-	val = val & 0xffff;
-      else if (len == 3)
-	val = val & 0xffffff;
-      debug_printf ("Writing %0*x to 0x%08lx in process %d\n",
-		    2 * ((len < 4) ? len : 4), val, (long)memaddr, pid);
+      char str[4 * 2 + 1];
+      char *p = str;
+      int dump = len < 4 ? len : 4;
+
+      for (i = 0; i < dump; i++)
+	{
+	  sprintf (p, "%02x", myaddr[i]);
+	  p += 2;
+	}
+      *p = '\0';
+
+      debug_printf ("Writing %s to 0x%08lx in process %d\n",
+		    str, (long) memaddr, pid);
     }
 
   /* Fill start and end extra bytes of buffer with existing memory data.  */
diff --git a/gdb/nat/linux-waitpid.c b/gdb/nat/linux-waitpid.c
index 97149bd..cbcdd95 100644
--- a/gdb/nat/linux-waitpid.c
+++ b/gdb/nat/linux-waitpid.c
@@ -144,7 +144,7 @@ my_waitpid (int pid, int *status, int flags)
     }
 
   linux_debug ("my_waitpid (%d, 0x%x): status(%x), %d\n",
-	       pid, flags, status ? *status : -1, ret);
+	       pid, flags, (ret > 0 && status != NULL) ? *status : -1, ret);
 
   errno = out_errno;
   return ret;