From: Alex Rousskov <rousskov@measurement-factory.com>
Date: Sun, 2 Apr 2023 07:42:10 +0000 (+0000)
Subject: Fix GCC v13 build [-Warray-bounds] (#1318)
X-Git-Tag: SQUID_7_0_1~457
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6f6db8c5b76b4e49059cd348d0e7afb3616f0e6b;p=thirdparty%2Fsquid.git

Fix GCC v13 build [-Warray-bounds] (#1318)

    src/ipc/mem/FlexibleArray.h:34:52: error: array subscript -1 is
    below array bounds of 'int [1]' [-Werror=array-bounds]

We suspect this warning is a GCC v13 regression bug because the callers
marked as problematic by GCC (e.g., Rock::LoadingEntry::LoadingEntry) do
not use "array subscript -1", and the Ipc::StoreMapItems::at() operator
they use even asserts that the subscript is not negative. It might be
GCC bug 107699: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107699

This change replaces the fake one-item array hack with a properly
aligned byte (still used as the "start of the real array" marker).

Also removed some unused and problematic code (instead of polishing it).
---

diff --git a/src/ipc/mem/FlexibleArray.h b/src/ipc/mem/FlexibleArray.h
index 6a0a4360b3..53ecd39a74 100644
--- a/src/ipc/mem/FlexibleArray.h
+++ b/src/ipc/mem/FlexibleArray.h
@@ -9,7 +9,7 @@
 #ifndef SQUID_IPC_MEM_FLEXIBLE_ARRAY_H
 #define SQUID_IPC_MEM_FLEXIBLE_ARRAY_H
 
-// sometimes required for placement-new operator to be declared
+#include <cstddef>
 #include <new>
 
 namespace Ipc
@@ -27,20 +27,15 @@ class FlexibleArray
 {
 public:
     explicit FlexibleArray(const int capacity) {
-        if (capacity > 1) // the first item is initialized automatically
-            new (raw()+1) Item[capacity-1];
+        new (raw()) Item[capacity];
     }
 
-    Item &operator [](const int idx) { return items[idx]; }
-    const Item &operator [](const int idx) const { return items[idx]; }
+    Item &operator [](const int idx) { return *(raw() + idx); }
 
-    //const Item *operator ()() const { return items; }
-    //Item *operator ()() { return items; }
-
-    Item *raw() { return items; }
+    Item *raw() { return reinterpret_cast<Item*>(&start_); }
 
 private:
-    Item items[1]; // ensures proper alignment of array elements
+    alignas(Item) std::byte start_; ///< the first byte of the first array item
 };
 
 } // namespace Mem