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[PATCH] Fix '-data-read-memory-bytes' typo/assertion

This patch fixes a typo in target.c:read_memory_robust, where
it calls read_whatever_is_readable with the function arguments
in the wrong order.  Depending on the address being read, it
can cause an xmalloc with a huge size, resulting in an assertion
failure, or just read something other than what was requested.

The problem only arises when GDB is handling an MI
"-data-read-memory-bytes" request and the initial target_read returns
an error status.  Note that read_memory_robust is only called from
the MI code.

Function definition:
  static void
  read_whatever_is_readable (struct target_ops *ops,
                             const ULONGEST begin, const ULONGEST end,
                             int unit_size,
                             VEC(memory_read_result_s) **result)

Function call:
    read_whatever_is_readable (ops, offset + xfered_total, unit_size,
                               offset + xfered_total + to_read, &result);

If we debug gdb, generate the error, and break just before the call to
read_whatever_is_readable, we see:

# Generate an error by trying to read a bogus address in the GDB
# that is under debug.
(gdb) interpreter-exec mi "-data-read-memory-bytes 1073741752 216"

# GDB-under-debug stops at the breakpoint on the call to
# read_whatever_is_readable.
Breakpoint 1, read_memory_robust (ops=0xe70150, offset=1073741752, len=216)
    at /scratch/dbreazea/sandbox/gdb-5611/binutils-gdb/gdb/target.c:1825
1825	              read_whatever_is_readable (ops, offset + xfered_total, unit_size,
(top) p unit_size
$1 = 1

# Step into the function.
(top) step
read_whatever_is_readable (ops=0xe70150, begin=1073741752, end=1, 
    unit_size=1073741968, result=0x7fffffffdd40)
    at /scratch/dbreazea/sandbox/gdb-5611/binutils-gdb/gdb/target.c:1658
1658	  gdb_byte *buf = (gdb_byte *) xmalloc (end - begin);

# unit_size was passed as 'end', and we are going to xmalloc a large
# number and assert.
(top) p end-begin
$2 = 18446744072635809865
(top) c
"/scratch/dbreazea/sandbox/gdb-5611/binutils-gdb/gdb/utils.c:1072: internal-error: virtual memory exhausted.\nA problem internal to GDB has been detected,\nfurther debugging may prove unreliable.\nQuit this debugging session? (y or n) "

# With the fixed version, (end - begin) gives the 'len' passed to
# read_memory_robust and specified by -data-read-memory-bytes
(top) p end-begin
$2 = 216

Tested on native x86_64 Linux with the gdb.mi tests.


2015-11-18  Don Breazeal  <>

	* gdb/target.c (read_memory_robust): Call
	read_whatever_is_readable with arguments in the correct order.

 gdb/target.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/gdb/target.c b/gdb/target.c
index 93786c3..950a1b7 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1822,8 +1822,9 @@ read_memory_robust (struct target_ops *ops,
 	      /* Got an error reading full chunk.  See if maybe we can read
 		 some subrange.  */
 	      xfree (buffer);
-	      read_whatever_is_readable (ops, offset + xfered_total, unit_size,
-					 offset + xfered_total + to_read, &result);
+	      read_whatever_is_readable (ops, offset + xfered_total,
+					 offset + xfered_total + to_read,
+					 unit_size, &result);
 	      xfered_total += to_read;

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