From a5850e1097515b9afd401a9bc6b265ced288c360 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <pitrou@free.fr>
Date: Fri, 18 Oct 2024 18:51:32 +0200
Subject: [PATCH] GH-44372: [C++] Fix unaligned load/store implementation for
 clang-18 (#44468)

### Rationale for this change

CLang 18 complains about undefined behavior when memcpy is called on a T-unaligned `T*` pointer.
This is due to this upstream change: https://github.com/llvm/llvm-project/pull/67766

### What changes are included in this PR?

Workaround by casting to `void*`.

### Are these changes tested?

By existing CI tests.

### Are there any user-facing changes?

No.

* GitHub Issue: #44372

Lead-authored-by: Antoine Pitrou <pitrou@free.fr>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>
---
 cpp/src/arrow/util/ubsan.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cpp/src/arrow/util/ubsan.h b/cpp/src/arrow/util/ubsan.h
index 900d8011dfd69..2308ee33519ca 100644
--- a/cpp/src/arrow/util/ubsan.h
+++ b/cpp/src/arrow/util/ubsan.h
@@ -63,7 +63,7 @@ inline std::enable_if_t<std::is_trivially_copyable_v<T>, T> SafeLoadAs(
 template <typename T>
 inline std::enable_if_t<std::is_trivially_copyable_v<T>, T> SafeLoad(const T* unaligned) {
   std::remove_const_t<T> ret;
-  std::memcpy(&ret, unaligned, sizeof(T));
+  std::memcpy(&ret, static_cast<const void*>(unaligned), sizeof(T));
   return ret;
 }
 
@@ -73,7 +73,7 @@ inline std::enable_if_t<std::is_trivially_copyable_v<T> &&
                         U>
 SafeCopy(T value) {
   std::remove_const_t<U> ret;
-  std::memcpy(&ret, &value, sizeof(T));
+  std::memcpy(&ret, static_cast<const void*>(&value), sizeof(T));
   return ret;
 }