Prelimit number of bytes to read in "vFile:pread:"

While handling "vFile:pread:" packets, gdbserver would read the
number of bytes requested regardless of whether this would fit
into the reply packet.  gdbserver would then return a packet's
worth of data and discard the remainder.  When accessing large
binaries GDB (via BFD) routinely makes large "vFile:pread:"
requests, resulting in gdbserver allocating large unnecessary
buffers and reading some portions of the file many times over.

This commit causes gdbserver to limit the number of bytes to be
read to a sensible maximum prior to allocating buffers and reading
data.

gdb/gdbserver/ChangeLog:

	* hostio.c (handle_pread): Do not attempt to read more data
	than hostio_reply_with_data can fit in a packet.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 2764d28f59bffbc376b640d4058ef2764be7affe..ef497492d952333e2f922e19f2797f006284cdc2 100644 (file)
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2015-08-19  Gary Benson  <gbenson@redhat.com>
+
+       * hostio.c (handle_pread): Do not attempt to read more data
+       than hostio_reply_with_data can fit in a packet.
+
 2015-08-18  Joel Brobecker  <brobecker@adacore.com>
 
        * linux-aarch32-low.c (NT_ARM_VFP): Define if not already defined.

diff --git a/gdb/gdbserver/hostio.c b/gdb/gdbserver/hostio.c
index b38a6bd05649a79677f0b0f8cdd89967c5daab04..8788f0739180f7c2642c6ea7487c24bc9fd49acf 100644 (file)
--- a/gdb/gdbserver/hostio.c
+++ b/gdb/gdbserver/hostio.c
@@ -344,6 +344,7 @@ handle_pread (char *own_buf, int *new_packet_len)
 {
   int fd, ret, len, offset, bytes_sent;
   char *p, *data;
+  static int max_reply_size = -1;
 
   p = own_buf + strlen ("vFile:pread:");
 
@@ -359,6 +360,17 @@ handle_pread (char *own_buf, int *new_packet_len)
       return;
     }
 
+  /* Do not attempt to read more than the maximum number of bytes
+     hostio_reply_with_data can fit in a packet.  We may still read
+     too much because of escaping, but this is handled below.  */
+  if (max_reply_size == -1)
+    {
+      sprintf (own_buf, "F%x;", PBUFSIZ);
+      max_reply_size = PBUFSIZ - strlen (own_buf);
+    }
+  if (len > max_reply_size)
+    len = max_reply_size;
+
   data = xmalloc (len);
 #ifdef HAVE_PREAD
   ret = pread (fd, data, len, offset);