[PATCH] Fix UB in string_slice::operator== (PR 121261)

[Alfie Richards]

Hi,

Small fix to resolve an UBSAN diagnostic.

Reg tested for Aarch64

Thanks,
Alfie

-- >8 --

This adds a nullptr check to fix a regression where it is possible to call
`memcmp (NULL, NULL, 0)` which is UB.

This should fix the bootstrap-ubsan build.

gcc/ChangeLog:
        PR middle-end/121261
        * vec.h: Add null ptr check.
---
 gcc/vec.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/vec.h b/gcc/vec.h
index 9604edb1c3c..1277a881f1c 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -2514,6 +2514,10 @@ public:
       return false;
     if (lhs.size () != rhs.size ())
       return false;
+    /* Case where either is a NULL pointer and therefore, as both are valid,
+       both are empty slices with length 0.  */
+    if (lhs.begin () == NULL || rhs.begin () == NULL)
+      return true;
     return memcmp (lhs.begin (), rhs.begin (), lhs.size ()) == 0;
   }
 
-- 
2.34.1