[PATCH 1/7] Emit a warning when writing to a readonly section and trust_readonly is true

[Yao Qi <yao@codesourcery.com>]

If users write a readonly section, such as .text, the contents of the inferior
and of the executable become out of sync.  It is better to emit a warning
to ask users to "set trust-readonly-sections off".

(gdb) set trust-readonly-sections on
(gdb) p /x* (char *) 0x080484c1 = 0xcc
warning: Writing to a readonly section so that the contents in the
inferior and in the executable are out of sync.  Please 'set
trust-readonly-sections off'.
$1 = 0xcc

gdb:

2013-09-08  Yao Qi  <yao@codesourcery.com>

	* target.c (memory_xfer_partial_1): Emit a warning if GDB
	writes to a readonly section and 'trust_readonly' is true.
---
 gdb/target.c |   31 ++++++++++++++++++++++---------
 1 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/gdb/target.c b/gdb/target.c
index d55712d..f6a58ff 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1471,11 +1471,13 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
 	}
     }
 
-  /* Try the executable files, if "trust-readonly-sections" is set.  */
-  if (readbuf != NULL && trust_readonly)
+  /* If "trust-readonly-sections" is set, read from the executable
+     files.  When GDB writes to a readonly section of the inferior,
+     emit a warning that option 'trust-readonly-sections' should be
+     turned off.  */
+  if (trust_readonly)
     {
       struct target_section *secp;
-      struct target_section_table *table;
 
       secp = target_section_by_addr (ops, memaddr);
       if (secp != NULL
@@ -1483,12 +1485,23 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
 				     secp->the_bfd_section)
 	      & SEC_READONLY))
 	{
-	  table = target_get_section_table (ops);
-	  return section_table_xfer_memory_partial (readbuf, writebuf,
-						    memaddr, len,
-						    table->sections,
-						    table->sections_end,
-						    NULL);
+
+	  if (readbuf != NULL)
+	    {
+	      struct target_section_table *table;
+
+	      table = target_get_section_table (ops);
+	      return section_table_xfer_memory_partial (readbuf, writebuf,
+							memaddr, len,
+							table->sections,
+							table->sections_end,
+							NULL);
+	    }
+
+	  if (writebuf != NULL)
+	    warning (_("Writing to a readonly section so that the contents"
+		       " in the inferior and in the executable are out of"
+		       " sync.  Please 'set trust-readonly-sections off'."));
 	}
     }
 
-- 
1.7.7.6