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Re: [PATCH][BZ #16004] Check overlaps in memcpy_chk.

On Mon, Oct 21, 2013 at 05:50:12PM +0000, Joseph S. Myers wrote:
> On Mon, 21 Oct 2013, Ondrej Bilka wrote:
> > On Sat, Oct 05, 2013 at 07:28:27PM +0000, Joseph S. Myers wrote:
> > > There are tests for *_chk functions in debug/.  If you add a new check you 
> > > should also add testcases for it to confirm that the error is caught at 
> > > runtime.  This does of course require also adding the same check to the 
> > > generic version of the function, and in the case of memcpy_chk to the x86 
> > > (32-bit) versions as well.
> > > 
> > It also requires to edit compile time check. I spend hour trying to
> > write testcase and wondering where is error until I realized that it got
> > optimized away at compile time.
> I'm not clear what compile-time check you're referring to.  If it's 
> something in GCC, it's certainly reasonable to build testcases with 
> -fno-builtin-<function>.  But really, if the error can be detected at 
> compile time, GCC should be able to do so - and for examples that can't be 
> detected at compile time, you can always use "volatile" to ensure the 
> compiler has no information about the actual values of function arguments.
> -- 
> Joseph S. Myers

I tried to add it in following way. As buf has size 10 current checker
decided that no overflow was possible.

diff --git a/debug/tst-chk1.c b/debug/tst-chk1.c
index 6ca8d9d..51aea96 100644
--- a/debug/tst-chk1.c
+++ b/debug/tst-chk1.c
@@ -281,6 +281,12 @@ do_test (void)
+  /* Now check if all overlapping buffers are caught at runtime.  */
+  memcpy (buf, buf + 3, 5);
   /* Now check if all buffer overflows are caught at runtime.  */

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