0001-HACK-Warn-for-bug-95189.patch

From dcc2606d510cc382fd2a9ab387ac99f2423d3973 Mon Sep 17 00:00:00 2001
From: Tim Ruffing <crypto@timruffing.de>
Date: Fri, 25 Sep 2020 11:51:43 +0200
Subject: [PATCH] HACK: Warn for bug 95189

---
 gcc/builtins.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gcc/builtins.c b/gcc/builtins.c
index 53bae599d3e..0935a668570 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -7663,6 +7663,14 @@ inline_expand_builtin_string_cmp (tree exp, rtx target)
 
   machine_mode mode = TYPE_MODE (TREE_TYPE (exp));
 
+  /* HACK */
+  if (fcode == BUILT_IN_MEMCMP && length < len3)
+    {
+      location_t loc = EXPR_HAS_LOCATION(exp) ? EXPR_LOCATION (exp) : UNKNOWN_LOCATION;
+      loc = expansion_point_location_if_in_system_header(loc);
+      emit_diagnostic(DK_DEBUG, loc, 0, "Potentially miscompiled memcmp");
+    }
+
   /* Now, start inline expansion the call.  */
   return inline_string_cmp (target, (const_str_n == 1) ? arg2 : arg1,
 			    (const_str_n == 1) ? src_str1 : src_str2, length,
-- 
2.28.0

coauthored by @roconnor-blockstream