[RFA/commit] Memory leak in on reading frame register

[Joel Brobecker <brobecker@adacore.com>]

[On behalf of Jerome  Guitton]

When using a conditional breakpoint where the condition evaluated
to false a large number of times before the program stopped,
a user reported that GDB's memory consumption was growing very
quickly until it ran out of memory.

The problem was tracked down to temporary struct values being created
each time the program stops and we evaluate those conditions. This
patch fixes the issue by releasing the temporary values, and adds
a comment explaining why we do that.

gdb/ChangeLog:

        Jerome Guitton  <guitton@adacore.com>:
	* findvar.c (read_frame_register_value): Fix a memory leak.

Tested on x86_64-linux. No regression.

I'll push the patch in a week or so, pending comments.

Thanks,
-- 
Joel

---
 gdb/findvar.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/gdb/findvar.c b/gdb/findvar.c
index 2079b4b..8ccf267 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -686,6 +686,17 @@ read_frame_register_value (struct value *value, struct frame_info *frame)
 
       value_contents_copy (value, offset, regval, reg_offset, reg_len);
 
+      /* Release regval right away, as we know we do not need it anymore.
+	 Otherwise, those values just keep accumulating until they finally
+	 get released when the current command finishes (as part of the
+	 all_values chain cleanup).  While this works most of the time,
+	 we have observed that, when using a conditional breakpoint where
+	 the condition gets repeatedly evaluated to false, keeping those
+	 values in memory causes a rapid and measurable growth in memory
+	 consumption, eventually leading us to running out of memory.  */
+      release_value (regval);
+      value_free (regval);
+
       offset += reg_len;
       len -= reg_len;
       reg_offset = 0;
-- 
1.9.1