Improve SDT checksum functions

Makefile

@@ -7,7 +7,7 @@ LIBS    = -L$(GNUEFI_LIB) -lefi -lgcc
 GNUEFI_INC = /usr/$(CC_PREFIX)/include/efi
 GNUEFI_LIB = /usr/$(CC_PREFIX)/lib
 
-FILES_C = src/main.c src/util.c src/config.c
+FILES_C = src/main.c src/util.c src/types.c src/config.c
 FILES_H = $(wildcard src/*.h)
 
 .PHONY: all

src/main.c

@@ -95,8 +95,7 @@ static void FillBGRT(ACPI_BGRT* bgrt, BMP* new_bmp, int new_x, int new_y) {
 	bgrt->image_offset_y = SelectCoordinate(new_y, y_auto, bgrt0.image_offset_y);
 	Debug(L"HackBGRT: BMP at (%d, %d).\n", (int) bgrt->image_offset_x, (int) bgrt->image_offset_y);
 
-	bgrt->header.checksum = 0;
+	SetAcpiSdtChecksum(bgrt);
-	bgrt->header.checksum = CalculateAcpiChecksum(bgrt, bgrt->header.length);
 }
 
 /**

src/types.c

@@ -0,0 +1,37 @@
+#include "types.h"
+
+UINT8 SumBytes(const UINT8* arr, UINTN size) {
+	UINT8 sum = 0;
+	for (UINTN i = 0; i < size; ++i) {
+		sum += arr[i];
+	}
+	return sum;
+}
+
+int VerifyAcpiRsdp2Checksums(const void* data) {
+	const UINT8* arr = data;
+	UINTN size = *(const UINT32*)&arr[20];
+	return SumBytes(arr, 20) == 0 && SumBytes(arr, size) == 0;
+}
+
+void SetAcpiRsdp2Checksums(void* data) {
+	UINT8* arr = data;
+	UINTN size = *(const UINT32*)&arr[20];
+	arr[9] = 0;
+	arr[32] = 0;
+	arr[9] = -SumBytes(arr, 20);
+	arr[32] = -SumBytes(arr, size);
+}
+
+int VerifyAcpiSdtChecksum(const void* data) {
+	const UINT8* arr = data;
+	UINTN size = *(const UINT32*)&arr[4];
+	return SumBytes(arr, size) == 0;
+}
+
+void SetAcpiSdtChecksum(void* data) {
+	UINT8* arr = data;
+	UINTN size = *(const UINT32*)&arr[4];
+	arr[9] = 0;
+	arr[9] = -SumBytes(arr, size);
+}

src/types.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <efi.h>
+
 #pragma pack(push, 1)
 
 /** RSDP (Root System Description Pointer) */
@@ -51,4 +53,35 @@ typedef struct {
 	UINT16 planes;
 	UINT16 bpp;
 } BMP;
+
+/**
+ * Verify the checksums of an ACPI RSDP version 2.
+ *
+ * @param data Pointer to the table.
+ * @return 1 if the checksum is correct, 0 otherwise.
+ */
+extern int VerifyAcpiRsdp2Checksums(const void* data);
+
+/**
+ * Set the correct checksums of an ACPI RSDP version 2.
+ *
+ * @param data Pointer to the table.
+ */
+extern void SetAcpiRsdp2Checksums(void* data);
+
+/**
+ * Verify the checksum of an ACPI SDT.
+ *
+ * @param data Pointer to the table.
+ * @return 1 if the checksum is correct, 0 otherwise.
+ */
+extern int VerifyAcpiSdtChecksum(const void* data);
+
+/**
+ * Set the correct checksum for an ACPI SDT.
+ *
+ * @param data Pointer to the table.
+ */
+extern void SetAcpiSdtChecksum(void* data);
+
 #pragma pack(pop)

src/util.c

@@ -18,15 +18,6 @@ UINTN NullPrint(IN CHAR16 *fmt, ...) {
 	return 0;
 }
 
-UINT8 CalculateAcpiChecksum(void* data, UINTN size) {
-	UINT8 sum = 0;
-	UINT8* arr = data;
-	for (UINTN i = 0; i < size; ++i) {
-		sum += arr[i];
-	}
-	return 256 - sum;
-}
-
 const CHAR16* TrimLeft(const CHAR16* s) {
 	// Skip white-space and BOM.
 	while (s[0] == L'\xfeff' || s[0] == ' ' || s[0] == '\t') {

src/util.h

@@ -16,15 +16,6 @@ extern const CHAR16* TmpStr(CHAR8 *src, int length);
  */
 extern UINTN NullPrint(IN CHAR16 *fmt, ...);
 
-/**
- * Calculate the checksum for an ACPI table.
- *
- * @param data Pointer to the table.
- * @param size Table length in bytes.
- * @return Checksum.
- */
-extern UINT8 CalculateAcpiChecksum(void* data, UINTN size);
-
 /**
  * Return the greater of two numbers.
  */