efi: add EFI_SYSTEM_TABLE_POINTER for debug

Add EFI_SYSTEM_TABLE_POINTER structure for remote debugger to locate
the address of EFI_SYSTEM_TABLE.

This feature is described in UEFI SPEC version 2.10. Section 18.4.2.
The implementation ensures support for hardware-assisted debugging and
provides a standardized mechanism for debuggers to discover the EFI
system table.

Cc: Peter Robinson <[email protected]>
Cc: Simon Glass <[email protected]>
Signed-off-by: Ying-Chun Liu (PaulLiu) <[email protected]>
Reviewed-by: Ilias Apalodimas <[email protected]>
Tested-by: Heinrich Schuchardt <[email protected]>
Reviewed-by: Heinrich Schuchardt <[email protected]> # change memset(systab_pointer, 0 ...) -> systab_pointer->crc32 = 0;
Signed-off-by: Ilias Apalodimas <[email protected]>

1 files changed, 40 insertions, 0 deletions

diff --git a/lib/efi_loader/efi_debug_support.c b/lib/efi_loader/efi_debug_support.c
new file mode 100644
index 00000000000..649d21ef829
--- /dev/null
+++ b/lib/efi_loader/efi_debug_support.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * EFI debug support
+ *
+ * Copyright (c) 2025 Ying-Chun Liu, Linaro Ltd. <[email protected]>
+ */
+
+#include <efi_loader.h>
+#include <linux/sizes.h>
+#include <u-boot/crc.h>
+
+struct efi_system_table_pointer __efi_runtime_data * systab_pointer = NULL;
+
+/**
+ * efi_initialize_system_table_pointer() - Initialize system table pointer
+ *
+ * Return:	status code
+ */
+efi_status_t efi_initialize_system_table_pointer(void)
+{
+	/* Allocate efi_system_table_pointer structure with 4MB alignment. */
+	systab_pointer = efi_alloc_aligned_pages(sizeof(struct efi_system_table_pointer),
+						 EFI_RUNTIME_SERVICES_DATA,
+						 SZ_4M);
+
+	if (!systab_pointer) {
+		log_err("Installing EFI system table pointer failed\n");
+		return EFI_OUT_OF_RESOURCES;
+	}
+
+	systab_pointer->crc32 = 0;
+
+	systab_pointer->signature = EFI_SYSTEM_TABLE_SIGNATURE;
+	systab_pointer->efi_system_table_base = (uintptr_t)&systab;
+	systab_pointer->crc32 = crc32(0,
+				      (const unsigned char *)systab_pointer,
+				      sizeof(struct efi_system_table_pointer));
+
+	return EFI_SUCCESS;
+}