From a4b36cd0d5901f6142596bda39ddad67c86a71cc Mon Sep 17 00:00:00 2001
From: Sergey Sharybin <sergey@blender.org>
Date: Fri, 12 Apr 2024 17:22:46 +0200
Subject: [PATCH] Guarded allocator: Ensure alignment and size of MemHead

Ensure that the MemHead and MemHeadAligned are such that memory
allocation followed with the head offset keeps the allocation
aligned to at least MEM_MIN_CPP_ALIGNMENT.

Pull Request: https://projects.blender.org/blender/blender/pulls/120582
---
 intern/guardedalloc/MEM_guardedalloc.h              | 7 +++++++
 intern/guardedalloc/intern/mallocn_guarded_impl.cc  | 2 ++
 intern/guardedalloc/intern/mallocn_lockfree_impl.cc | 4 ++++
 3 files changed, 13 insertions(+)

diff --git a/intern/guardedalloc/MEM_guardedalloc.h b/intern/guardedalloc/MEM_guardedalloc.h
index e142802e6c5..02011da11cb 100644
--- a/intern/guardedalloc/MEM_guardedalloc.h
+++ b/intern/guardedalloc/MEM_guardedalloc.h
@@ -258,6 +258,13 @@ void MEM_use_guarded_allocator(void);
 #  include <type_traits>
 #  include <utility>
 
+/* Conservative value of memory alignment returned by non-aligned OS-level memory allocation
+ * functions. For alignments smaller than this value, using non-aligned versions of allocator API
+ * functions is okay, allowing use of calloc, for example. */
+#  define MEM_MIN_CPP_ALIGNMENT \
+    (__STDCPP_DEFAULT_NEW_ALIGNMENT__ < alignof(void *) ? __STDCPP_DEFAULT_NEW_ALIGNMENT__ : \
+                                                          alignof(void *))
+
 /**
  * Allocate new memory for and constructs an object of type #T.
  * #MEM_delete should be used to delete the object. Just calling #MEM_freeN is not enough when #T
diff --git a/intern/guardedalloc/intern/mallocn_guarded_impl.cc b/intern/guardedalloc/intern/mallocn_guarded_impl.cc
index 39c389e9e7e..3efeea6f039 100644
--- a/intern/guardedalloc/intern/mallocn_guarded_impl.cc
+++ b/intern/guardedalloc/intern/mallocn_guarded_impl.cc
@@ -129,6 +129,8 @@ typedef struct MemHead {
 #endif
 
 } MemHead;
+static_assert(MEM_MIN_CPP_ALIGNMENT <= alignof(MemHead), "Bad alignment of MemHead");
+static_assert(MEM_MIN_CPP_ALIGNMENT <= sizeof(MemHead), "Bad size of MemHead");
 
 typedef MemHead MemHeadAligned;
 
diff --git a/intern/guardedalloc/intern/mallocn_lockfree_impl.cc b/intern/guardedalloc/intern/mallocn_lockfree_impl.cc
index 82d14e990db..e154c17cf6d 100644
--- a/intern/guardedalloc/intern/mallocn_lockfree_impl.cc
+++ b/intern/guardedalloc/intern/mallocn_lockfree_impl.cc
@@ -32,11 +32,15 @@ typedef struct MemHead {
   /* Length of allocated memory block. */
   size_t len;
 } MemHead;
+static_assert(MEM_MIN_CPP_ALIGNMENT <= alignof(MemHead), "Bad alignment of MemHead");
+static_assert(MEM_MIN_CPP_ALIGNMENT <= sizeof(MemHead), "Bad size of MemHead");
 
 typedef struct MemHeadAligned {
   short alignment;
   size_t len;
 } MemHeadAligned;
+static_assert(MEM_MIN_CPP_ALIGNMENT <= alignof(MemHeadAligned), "Bad alignment of MemHeadAligned");
+static_assert(MEM_MIN_CPP_ALIGNMENT <= sizeof(MemHeadAligned), "Bad size of MemHeadAligned");
 
 static bool malloc_debug_memset = false;