fs, devices: fix undefined behavior in registration

1 files changed, 13 insertions, 4 deletions

diff --git a/arch/x86_64/kapi/devices.cpp b/arch/x86_64/kapi/devices.cpp
index 39dbc010..b2e9cba5 100644
--- a/arch/x86_64/kapi/devices.cpp
+++ b/arch/x86_64/kapi/devices.cpp
@@ -9,6 +9,7 @@
 #include <kstd/memory.hpp>
 #include <kstd/print.hpp>
 
+#include <new>
 #include <ranges>
 #include <span>
 #include <utility>
@@ -24,16 +25,24 @@ namespace kapi::devices
   extern "C"
   {
     // We need to suppress clang-tidy linting warnings here, since these symbols are generated by the linker and we
-    // cannot choose their names, unless we wanted to extend the linker script needlessly.
+    // cannot choose their names, unless we want to write a bht linker script for no reason. Additionally, these symbols
+    // need to be arrays, because otherwise any pointer arithmetic on them, beyond trivial cases of adding 0 or 1, is
+    // undefined behavior by the rules of the C++ abstract machine. To ensure the compiler does not try to perform
+    // constant folding, the pointers, these arrays of unknown bound decay to, need to be laundered before dereferencing
+    // them.
+
     // NOLINTBEGIN(readability-identifier-naming)
-    extern kstd::observer_ptr<kapi::devices::driver_descriptor> const __start_platform_drivers;
-    extern kstd::observer_ptr<kapi::devices::driver_descriptor> const __stop_platform_drivers;
+    extern kstd::observer_ptr<kapi::devices::driver_descriptor> const __start_platform_drivers[];
+    extern kstd::observer_ptr<kapi::devices::driver_descriptor> const __stop_platform_drivers[];
     // NOLINTEND(readability-identifier-naming)
   }
 
   auto init_platform_drivers() -> void
   {
-    auto descriptors = std::span{&__start_platform_drivers, &__stop_platform_drivers} |  //
+    auto clean_start = std::launder(__start_platform_drivers);
+    auto clean_stop = std::launder(__stop_platform_drivers);
+
+    auto descriptors = std::span{clean_start, clean_stop} |  //
                        std::views::filter([](auto p) { return p != nullptr; });
 
     for (auto driver : descriptors)