[PATCH v2 1/1] efi_loader: implement a HOB list

[Heinrich Schuchardt]

The debug version of the UEFI shell on x86 requires a HOB list.
This implementation allows to generate an empty HOB list.

Generate the HOB list on the sandbox and on x86 by default.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
v2:
	Free allocated memory if efi_install_configuration_table() fails.
---
 include/efi_hob.h          | 32 ++++++++++++++++++++++++++++++++
 include/efi_loader.h       |  9 +++++++++
 lib/efi_loader/Kconfig     |  8 ++++++++
 lib/efi_loader/Makefile    |  1 +
 lib/efi_loader/efi_hob.c   | 38 ++++++++++++++++++++++++++++++++++++++
 lib/efi_loader/efi_setup.c |  7 +++++++
 6 files changed, 95 insertions(+)
 create mode 100644 include/efi_hob.h
 create mode 100644 lib/efi_loader/efi_hob.c

diff --git a/include/efi_hob.h b/include/efi_hob.h
new file mode 100644
index 00000000000..b401e6c2fa1
--- /dev/null
+++ b/include/efi_hob.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  HOB list
+ *
+ *  Copyright (c) 2025 Heinrich Schuchardt
+ */
+
+#ifndef _EFI_HOB_H
+#define _EFI_HOB_H 1
+
+#include <efi.h>
+
+/**
+ * define EFI_HOB_TYPE_END_OF_HOB_LIST - end of hob list
+ */
+#define EFI_HOB_TYPE_END_OF_HOB_LIST	0xFFFF
+
+/**
+ * struct efi_hob_header - EFI_HOB_GENERIC_HEADER
+ */
+struct efi_hob_header {
+	/** @hob_type:		type of HOB data structure */
+	u16 hob_type;
+	/** @hob_length:	HOB length including header in bytes */
+	u16 hob_length;
+	/** @reserved:		always 0 */
+	u32 reserved;
+};
+
+extern const efi_guid_t efi_guid_hob_list;
+
+#endif /* _EFI_HOB_H */
diff --git a/include/efi_loader.h b/include/efi_loader.h
index 3e70ac07055..6183da64196 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -714,6 +714,15 @@ efi_status_t efi_acpi_register(void);
  */
 efi_status_t efi_smbios_register(void);
 
+/**
+ * efi_hob_list_register() - install HOB list
+ *
+ * The EFI shell on X86 requires a HOB list
+ *
+ * Return:	status code
+ */
+efi_status_t efi_hob_list_register(void);
+
 struct efi_simple_file_system_protocol *
 efi_fs_from_path(struct efi_device_path *fp);
 
diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index 13e44be1d06..b4f0d1dc23a 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -406,6 +406,14 @@ config EFI_LOADER_HII
 	  U-Boot implements enough of its features to be able to run the UEFI
 	  Shell, but not more than that.
 
+config EFI_HOB
+	bool 'HOB list'
+	default y if SANDBOX || X86
+	help
+	  Install a HOB list. The UEFI shell on x86 requires a HOB list
+	  to be present. Our list is empty as we don't implement the
+	  UEFI Platform Initialization Specification.
+
 config EFI_UNICODE_COLLATION_PROTOCOL2
 	bool "Unicode collation protocol"
 	default y
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index bfa607c8827..f010101125f 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -39,6 +39,7 @@ obj-y += efi_dt_fixup.o
 obj-y += efi_fdt.o
 obj-y += efi_file.o
 obj-$(CONFIG_EFI_LOADER_HII) += efi_hii.o efi_hii_config.o
+obj-$(CONFIG_EFI_HOB) += efi_hob.o
 obj-y += efi_image_loader.o
 obj-y += efi_load_options.o
 obj-y += efi_memory.o
diff --git a/lib/efi_loader/efi_hob.c b/lib/efi_loader/efi_hob.c
new file mode 100644
index 00000000000..f15439d31e0
--- /dev/null
+++ b/lib/efi_loader/efi_hob.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Provide HOB list
+ *
+ *  Copyright (c) 2025 Heinrich Schuchardt
+ */
+
+#include <efi_hob.h>
+#include <efi_loader.h>
+
+const efi_guid_t efi_guid_hob_list = EFI_HOB_LIST;
+
+/**
+ * efi_hob_list_register() - install HOB list
+ *
+ * The EFI shell on X86 requires a HOB list
+ *
+ * Return:	status code
+ */
+efi_status_t efi_hob_list_register(void)
+{
+	struct efi_hob_header *hob;
+	efi_status_t ret;
+
+	hob = efi_alloc(sizeof(struct efi_hob_header));
+	if (!hob)
+		return EFI_OUT_OF_RESOURCES;
+
+	hob->hob_type = EFI_HOB_TYPE_END_OF_HOB_LIST;
+	hob->hob_length = sizeof(struct efi_hob_header);
+	hob->reserved = 0;
+
+	ret = efi_install_configuration_table(&efi_guid_hob_list, hob);
+	if (ret != EFI_SUCCESS)
+		efi_free_pool(hob);
+
+	return ret;
+}
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c
index f06cf49e443..e9b6ffd27b8 100644
--- a/lib/efi_loader/efi_setup.c
+++ b/lib/efi_loader/efi_setup.c
@@ -7,6 +7,7 @@
 
 #define LOG_CATEGORY LOGC_EFI
 
+#include <efi_hob.h>
 #include <efi_loader.h>
 #include <efi_variable.h>
 #include <log.h>
@@ -308,6 +309,12 @@ efi_status_t efi_init_obj_list(void)
 			goto out;
 	}
 
+	if (IS_ENABLED(CONFIG_EFI_HOB)) {
+		ret = efi_hob_list_register();
+		if (ret != EFI_SUCCESS)
+			goto out;
+	}
+
 	if (IS_ENABLED(CONFIG_EFI_TCG2_PROTOCOL)) {
 		ret = efi_tcg2_register();
 		if (ret != EFI_SUCCESS)
-- 
2.51.0