Re: [RFC PATCH] -fsanitize=pointer-overflow support (PR sanitizer/80998)

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Jun 20, 2017 at 09:41:43AM +0200, Richard Biener wrote:
> > 2) libcpp/line-map.c has this:
> > static int
> > location_adhoc_data_update (void **slot, void *data)
> > {
> >   *((char **) slot) += *((int64_t *) data);
> >   return 1;
> > }
> > where the (why int64_t always?, we really need just intptr_t) adjusts
> > one pointer from an unrelated one (result of realloc).  That is a UB
> > and actually can trigger this sanitization if the two regions are
> > far away from each other, e.g. on i686-linux:
> > ../../libcpp/line-map.c:102:21: runtime error: pointer index expression with base 0x0899e308 overflowed to 0xf74c4ab8
> > ../../libcpp/line-map.c:102:21: runtime error: pointer index expression with base 0x08add7c0 overflowed to 0xf74c9a08
> > ../../libcpp/line-map.c:102:21: runtime error: pointer index expression with base 0x092ba308 overflowed to 0xf741cab8
> > ../../libcpp/line-map.c:102:21: runtime error: pointer index expression with base 0x0a3757c0 overflowed to 0xf7453a08
> > Shall we perform the addition in uintptr_t instead to make it
> > implementation defined rather than UB?
> 
> Yes.

Here is a patch for 2), bootstrap-ubsan bootstrapped/regtested on
x86_64-linux and i686-linux, ok for trunk?

Note both ptrdiff_t and uintptr_t are already used in libcpp, so I think
it shouldn't create new portability issues.

2017-06-21  Jakub Jelinek  <jakub@redhat.com>

	* line-map.c (location_adhoc_data_update): Perform addition in
	uintptr_t type rather than char * type.  Read *data using
	ptrdiff_t type instead of int64_t.
	(get_combined_adhoc_loc): Change offset type to ptrdiff_t from
	int64_t.

--- libcpp/line-map.c.jj	2017-06-19 08:28:18.000000000 +0200
+++ libcpp/line-map.c	2017-06-20 16:43:25.193063344 +0200
@@ -99,7 +99,8 @@ location_adhoc_data_eq (const void *l1,
 static int
 location_adhoc_data_update (void **slot, void *data)
 {
-  *((char **) slot) += *((int64_t *) data);
+  *((char **) slot)
+    = (char *) ((uintptr_t) *((char **) slot) + *((ptrdiff_t *) data));
   return 1;
 }
 
@@ -221,7 +222,7 @@ get_combined_adhoc_loc (struct line_maps
 	  set->location_adhoc_data_map.allocated)
 	{
 	  char *orig_data = (char *) set->location_adhoc_data_map.data;
-	  int64_t offset;
+	  ptrdiff_t offset;
 	  /* Cast away extern "C" from the type of xrealloc.  */
 	  line_map_realloc reallocator = (set->reallocator
 					  ? set->reallocator


	Jakub