From 1c5985148c8e03fddb1df1e4dccc10b14f2b583f Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Mon, 30 Oct 2023 17:51:18 +0200
Subject: [PATCH] Kernel: Allow offsetof with packed fields

This is not standard C++ but should be fine with my toolchain.
---
 kernel/CMakeLists.txt  | 3 +++
 kernel/kernel/ACPI.cpp | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/CMakeLists.txt b/kernel/CMakeLists.txt
index d7e140a5..bbc24efc 100644
--- a/kernel/CMakeLists.txt
+++ b/kernel/CMakeLists.txt
@@ -148,6 +148,9 @@ target_compile_options(kernel PUBLIC $<$<COMPILE_LANGUAGE:CXX>:-Wno-literal-suff
 target_compile_options(kernel PUBLIC -fmacro-prefix-map=${CMAKE_CURRENT_SOURCE_DIR}=.)
 target_compile_options(kernel PUBLIC -fstack-protector -ffreestanding -Wall -Werror=return-type -Wstack-usage=1024 -fno-omit-frame-pointer -mgeneral-regs-only)
 
+# This might not work with other toolchains
+target_compile_options(kernel PUBLIC $<$<COMPILE_LANGUAGE:CXX>:-Wno-invalid-offsetof>)
+
 if(ENABLE_KERNEL_UBSAN)
 	target_compile_options(kernel PUBLIC -fsanitize=undefined)
 endif()
diff --git a/kernel/kernel/ACPI.cpp b/kernel/kernel/ACPI.cpp
index 86ac0a3a..e853a253 100644
--- a/kernel/kernel/ACPI.cpp
+++ b/kernel/kernel/ACPI.cpp
@@ -213,7 +213,7 @@ namespace Kernel
 				auto* fadt = (FADT*)header;
 
 				paddr_t dsdt_paddr = 0;
-				if (fadt->length > 140) // 140 is the offset of x_dsdt
+				if (fadt->length > offsetof(FADT, x_dsdt))
 					dsdt_paddr = fadt->x_dsdt;
 				if (dsdt_paddr == 0 || !PageTable::is_valid_pointer(dsdt_paddr))
 					dsdt_paddr = fadt->dsdt;