Re: [PATCH PR gdb/15236] gdbserver write to linux memory with zero length corrupts stack

[Jeremy Bennett <jeremy.bennett@embecosm.com>]

On Wed, 2013-03-06 at 19:06 +0000, Pedro Alves wrote: 
> Hi Jeremy,
> 
> Thanks for the diagnosis and the patch.

Pedro, thanks for the comments. I've revised the patch accordingly.
Since I don't have write permission, would you commit it for me. Here is
the corrected ChangeLog entry:

2013-03-07  Jeremy Bennett  <jeremy.bennett@embecosm.com>

	PR gdb/15236
	* linux-low.c (linux_write_memory): Return early success if LEN is
	zero.

Here is the corrected patch:

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index a8cf78c..d7202fd 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,9 @@
+2013-03-07  Jeremy Bennett  <jeremy.bennett@embecosm.com>
+
+	PR gdb/15236
+	* linux-low.c (linux_write_memory): Return early success if LEN is
+	zero.
+
 2013-03-05  Corinna Vinschen  <vinschen@redhat.de>
 
 	* configure.srv: Add x86_64-*-cygwin* as target.
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index c52cd2e..8eb5dac 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -4481,7 +4481,7 @@ linux_read_memory (CORE_ADDR memaddr, unsigned char *myaddr, int len)
 
 /* Copy LEN bytes of data from debugger memory at MYADDR to inferior's
    memory at MEMADDR.  On failure (cannot write to the inferior)
-   returns the value of errno.  */
+   returns the value of errno.  Succeeds immediately if LEN is zero. */
 
 static int
 linux_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len)
@@ -4500,6 +4500,12 @@ linux_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len)
 
   int pid = lwpid_of (get_thread_lwp (current_inferior));
 
+  if (len == 0)
+    {
+      /* Zero length write always succeeds. */
+      return 0;
+    }
+
   if (debug_threads)
     {
       /* Dump up to four bytes.  */

Best wishes,


Jeremy

-- 
Tel:      +44 (1590) 610184
Cell:     +44 (7970) 676050
SkypeID: jeremybennett
Email:   jeremy.bennett@embecosm.com
Web:     www.embecosm.com