[PATCH v7 1/6] efi: add EFI_SYSTEM_TABLE_POINTER for debug
Heinrich Schuchardt
xypron.glpk at gmx.de
Tue Jul 1 08:29:43 CEST 2025
On 01.07.25 05:49, Ying-Chun Liu (PaulLiu) wrote:
> From: "Ying-Chun Liu (PaulLiu)" <paul.liu at linaro.org>
>
> 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.
>
> Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu at linaro.org>
> Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
> Cc: Peter Robinson <pbrobinson at gmail.com>
> Cc: Simon Glass <sjg at chromium.org>
> ---
> V2: add Kconfig options to turn on/off this feature.
> V3: make efi_initialize_system_table_pointer() do the job as described.
> V4: use efi_alloc_aligned_pages() for system_table_pointer.
> V5: move the code into a separate module.
> V6: Use macros to replace size_4MB
> V7: Fix the code based on the review. Update license field.
> ---
> include/efi_api.h | 16 ++++++++++++
> include/efi_loader.h | 2 ++
> lib/efi_loader/Kconfig | 8 ++++++
> lib/efi_loader/Makefile | 1 +
> lib/efi_loader/efi_debug_support.c | 40 ++++++++++++++++++++++++++++++
> lib/efi_loader/efi_setup.c | 7 ++++++
> 6 files changed, 74 insertions(+)
> create mode 100644 lib/efi_loader/efi_debug_support.c
>
> diff --git a/include/efi_api.h b/include/efi_api.h
> index eb61eafa028..6c4c1a0cc7b 100644
> --- a/include/efi_api.h
> +++ b/include/efi_api.h
> @@ -259,6 +259,22 @@ struct efi_capsule_result_variable_header {
> efi_status_t capsule_status;
> } __packed;
>
> +/**
> + * struct efi_system_table_pointer - struct to store the pointer of system
> + * table.
> + * @signature: The signature of this struct.
> + * @efi_system_table_base: The physical address of System Table.
> + * @crc32: CRC32 checksum
> + *
> + * This struct is design for hardware debugger to search through memory to
> + * get the address of EFI System Table.
> + */
> +struct efi_system_table_pointer {
> + u64 signature;
> + efi_physical_addr_t efi_system_table_base;
> + u32 crc32;
> +};
> +
> struct efi_memory_range {
> efi_physical_addr_t address;
> u64 length;
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index 8f9f2bcf1cb..8f065244d8e 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -646,6 +646,8 @@ efi_status_t efi_tcg2_measure_dtb(void *dtb);
> efi_status_t efi_root_node_register(void);
> /* Called by bootefi to initialize runtime */
> efi_status_t efi_initialize_system_table(void);
> +/* Called by bootefi to initialize debug */
> +efi_status_t efi_initialize_system_table_pointer(void);
> /* efi_runtime_detach() - detach unimplemented runtime functions */
> void efi_runtime_detach(void);
> /* efi_convert_pointer() - convert pointer to virtual address */
> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> index 7f02a83e2a2..f9d75cbc3fd 100644
> --- a/lib/efi_loader/Kconfig
> +++ b/lib/efi_loader/Kconfig
> @@ -71,6 +71,14 @@ config EFI_SECURE_BOOT
> config EFI_SIGNATURE_SUPPORT
> bool
>
> +config EFI_DEBUG_SUPPORT
> + bool "EFI Debug Support"
> + help
> + Select this option if you want to setup the EFI Debug Support
> + Table and the EFI_SYSTEM_TABLE_POINTER which is used by the debug
> + agent or an external debugger to determine loaded image information
> + in a quiescent manner.
> +
> menu "UEFI services"
>
> config EFI_GET_TIME
> diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
> index cf050e5385d..51ccf1cd87e 100644
> --- a/lib/efi_loader/Makefile
> +++ b/lib/efi_loader/Makefile
> @@ -70,6 +70,7 @@ obj-$(CONFIG_EFI_RISCV_BOOT_PROTOCOL) += efi_riscv.o
> obj-$(CONFIG_EFI_LOAD_FILE2_INITRD) += efi_load_initrd.o
> obj-$(CONFIG_EFI_SIGNATURE_SUPPORT) += efi_signature.o
> obj-$(CONFIG_EFI_ECPT) += efi_conformance.o
> +obj-$(CONFIG_EFI_DEBUG_SUPPORT) += efi_debug_support.o
>
> EFI_VAR_SEED_FILE := $(subst $\",,$(CONFIG_EFI_VAR_SEED_FILE))
> $(obj)/efi_var_seed.o: $(srctree)/$(EFI_VAR_SEED_FILE)
> diff --git a/lib/efi_loader/efi_debug_support.c b/lib/efi_loader/efi_debug_support.c
> new file mode 100644
> index 00000000000..c9773feaa5b
> --- /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. <paul.liu at linaro.org>
> + */
> +
> +#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;
> + }
> +
> + memset(systab_pointer, 0, sizeof(struct efi_system_table_pointer));
> +
> + systab_pointer->signature = EFI_SYSTEM_TABLE_SIGNATURE;
> + systab_pointer->efi_system_table_base = (efi_physical_addr_t)&systab;
> + systab_pointer->crc32 = crc32(0,
> + (const unsigned char *)systab_pointer,
> + sizeof(struct efi_system_table_pointer));
> +
> + return EFI_SUCCESS;
> +}
> diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c
> index 48f91da5df7..78c5059256a 100644
> --- a/lib/efi_loader/efi_setup.c
> +++ b/lib/efi_loader/efi_setup.c
> @@ -278,6 +278,13 @@ efi_status_t efi_init_obj_list(void)
> if (ret != EFI_SUCCESS)
> goto out;
>
> + /* Initialize system table pointer */
> + if (IS_ENABLED(CONFIG_EFI_DEBUG_SUPPORT)) {
> + ret = efi_initialize_system_table_pointer();
> + if (ret != EFI_SUCCESS)
> + goto out;
> + }
> +
> if (IS_ENABLED(CONFIG_EFI_ECPT)) {
> ret = efi_ecpt_register();
> if (ret != EFI_SUCCESS)
In the EFI shell I found:
RT_Data 00000000BDC00000-00000000BDC00FFF 0000000000000001
8000000000000008
And in gdb:
(gdb) p/x *(char[80]*)0x00000000bdc00000
$1 = {0x49, 0x42, 0x49, 0x20, 0x53, 0x59, 0x53, 0x54, 0xd0, 0xdf, 0x6b,
0xbf, 0x0, 0x0, 0x0, 0x0, 0x1d, 0x9a, 0x19, 0x33,
0x0 <repeats 60 times>}
(gdb) p/x *(char[16]*)0xbf6bdfd0
$2 = {0x49, 0x42, 0x49, 0x20, 0x53, 0x59, 0x53, 0x54, 0x6e, 0x0, 0x2,
0x0, 0x78, 0x0, 0x0, 0x0}
(gdb) p *(char[16]*)0xbf6bdfd0
$3 = "IBI SYSTn\000\002\000x\000\000"
This matches EFI_SYSTEM_TABLE_SIGNATURE 0x5453595320494249.
Tested-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
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