Global data

Globally required fields are held in the global data structure. A pointer to the structure is available as symbol gd. The symbol is made available by the macro %DECLARE_GLOBAL_DATA_PTR.

Register pointing to global data

On most architectures the global data pointer is stored in a register.

ARC	r25
ARM 32bit	r9
ARM 64bit	x18
M68000	d7
MicroBlaze	r31
Nios II	gp
PowerPC	r2
RISC-V	gp (x3)
SuperH	r13
x86 32bit	fs

The sandbox, x86_64, and Xtensa are notable exceptions.

Current implementation uses a register for the GD pointer because this results in smaller code. However, using plain global data for the GD pointer would be possible too (and simpler, as it does not require the reservation of a specific register for it), but the resulting code is bigger.

Clang for ARM does not support assigning a global register. When using Clang gd is defined as an inline function using assembly code. This adds a few bytes to the code size.

Binaries called by U-Boot are not aware of the register usage and will not conserve gd. UEFI binaries call the API provided by U-Boot and may return to U-Boot. The value of gd has to be saved every time U-Boot is left and restored whenever U-Boot is reentered. This is also relevant for the implementation of function tracing. For setting the value of gd function set_gd() can be used.

Global data structure

struct global_data: global data structure

Definition

struct global_data {
  struct bd_info *bd;
  unsigned long flags;
  unsigned int baudrate;
  unsigned long cpu_clk;
  unsigned long bus_clk;
  unsigned long pci_clk;
  unsigned long mem_clk;
#if CONFIG_IS_ENABLED(VIDEO);
  unsigned long fb_base;
#endif;
#if defined(CONFIG_POST);
  unsigned long post_log_word;
  unsigned long post_log_res;
  unsigned long post_init_f_time;
#endif;
#ifdef CONFIG_BOARD_TYPES;
  unsigned long board_type;
#endif;
  unsigned long have_console;
#if CONFIG_IS_ENABLED(PRE_CONSOLE_BUFFER);
  long precon_buf_idx;
#endif;
  unsigned long env_addr;
  unsigned long env_valid;
  unsigned long env_has_init;
  int env_load_prio;
  unsigned long ram_base;
  phys_addr_t ram_top;
  unsigned long relocaddr;
  phys_size_t ram_size;
  unsigned long mon_len;
  unsigned long irq_sp;
  unsigned long start_addr_sp;
  unsigned long reloc_off;
  struct global_data *new_gd;
#ifdef CONFIG_DM;
  struct udevice *dm_root;
  struct udevice *dm_root_f;
  struct list_head uclass_root_s;
  struct list_head *uclass_root;
# if CONFIG_IS_ENABLED(OF_PLATDATA_DRIVER_RT);
  struct driver_rt *dm_driver_rt;
# endif;
#if CONFIG_IS_ENABLED(OF_PLATDATA_RT);
  struct udevice_rt *dm_udevice_rt;
  void *dm_priv_base;
# endif;
#endif;
#ifdef CONFIG_TIMER;
  struct udevice *timer;
#endif;
  const void *fdt_blob;
  void *new_fdt;
  unsigned long fdt_size;
  enum fdt_source_t fdt_src;
#if CONFIG_IS_ENABLED(OF_LIVE);
  struct device_node *of_root;
#endif;
#if CONFIG_IS_ENABLED(MULTI_DTB_FIT);
  const void *multi_dtb_fit;
#endif;
  struct jt_funcs *jt;
  char env_buf[32];
#ifdef CONFIG_TRACE;
  void *trace_buff;
#endif;
#if CONFIG_IS_ENABLED(SYS_I2C_LEGACY);
  int cur_i2c_bus;
#endif;
  unsigned int timebase_h;
  unsigned int timebase_l;
#if CONFIG_IS_ENABLED(CMD_BDINFO_EXTRA);
  unsigned long malloc_start;
#endif;
#if CONFIG_IS_ENABLED(SYS_MALLOC_F);
  unsigned long malloc_base;
  unsigned long malloc_limit;
  unsigned long malloc_ptr;
#endif;
#ifdef CONFIG_PCI;
  struct pci_controller *hose;
  phys_addr_t pci_ram_top;
#endif;
#ifdef CONFIG_PCI_BOOTDELAY;
  int pcidelay_done;
#endif;
  struct udevice *cur_serial_dev;
  struct arch_global_data arch;
#ifdef CONFIG_CONSOLE_RECORD;
  struct membuff console_out;
  struct membuff console_in;
#endif;
#if CONFIG_IS_ENABLED(VIDEO);
  ulong video_top;
  ulong video_bottom;
#endif;
#ifdef CONFIG_BOOTSTAGE;
  struct bootstage_data *bootstage;
  struct bootstage_data *new_bootstage;
#endif;
#ifdef CONFIG_LOG;
  int log_drop_count;
  int default_log_level;
  struct list_head log_head;
  int log_fmt;
  bool processing_msg;
  int logc_prev;
  int logl_prev;
  bool log_cont;
#endif;
#if CONFIG_IS_ENABLED(BLOBLIST);
  struct bloblist_hdr *bloblist;
  struct bloblist_hdr *new_bloblist;
#endif;
#if CONFIG_IS_ENABLED(HANDOFF);
  struct spl_handoff *spl_handoff;
#endif;
#if defined(CONFIG_TRANSLATION_OFFSET);
  fdt_addr_t translation_offset;
#endif;
#ifdef CONFIG_ACPI;
  struct acpi_ctx *acpi_ctx;
  ulong acpi_start;
#endif;
#if CONFIG_IS_ENABLED(GENERATE_SMBIOS_TABLE);
  char *smbios_version;
#endif;
#if CONFIG_IS_ENABLED(EVENT);
  struct event_state event_state;
#endif;
#ifdef CONFIG_CYCLIC;
  struct hlist_head cyclic_list;
#endif;
  struct list_head dmtag_list;
};

Members

bd

board information

flags

global data flags

See enum gd_flags

baudrate

baud rate of the serial interface

cpu_clk

CPU clock rate in Hz

bus_clk

platform clock rate in Hz

pci_clk

PCI clock rate in Hz

mem_clk

memory clock rate in Hz

fb_base

base address of frame buffer memory

post_log_word

active POST tests

post_log_word is a bit mask defining which POST tests are recorded (see constants POST_*).

post_log_res

POST results

post_log_res is a bit mask with the POST results. A bit with value 1 indicates successful execution.

post_init_f_time

time in ms when post_init_f() started

board_type

board type

If a U-Boot configuration supports multiple board types, the actual board type may be stored in this field.

have_console

console is available

A value of 1 indicates that serial_init() was called and a console is available. A value of 0 indicates that console input and output drivers shall not be called.

precon_buf_idx

pre-console buffer index

precon_buf_idx indicates the current position of the buffer used to collect output before the console becomes available. When negative, the pre-console buffer is temporarily disabled (used when the pre-console buffer is being written out, to prevent adding its contents to itself).

env_addr

address of environment structure

env_addr contains the address of the structure holding the environment variables.

env_valid

environment is valid

See enum env_valid

env_has_init

bit mask indicating environment locations

enum env_location defines which bit relates to which location

env_load_prio

priority of the loaded environment

ram_base

base address of RAM used by U-Boot

ram_top

top address of RAM used by U-Boot

relocaddr

start address of U-Boot in RAM

After relocation this field indicates the address to which U-Boot has been relocated. It can be displayed using the bdinfo command. Its value is needed to display the source code when debugging with GDB using the ‘add-symbol-file u-boot <relocaddr>’ command.

ram_size

RAM size in bytes

mon_len

monitor length in bytes

irq_sp

IRQ stack pointer

start_addr_sp

initial stack pointer address

reloc_off

relocation offset

new_gd

pointer to relocated global data

dm_root

root instance for Driver Model

dm_root_f

pre-relocation root instance

uclass_root_s

head of core tree when uclasses are not in read-only memory.

When uclasses are in read-only memory, uclass_root_s is not used and uclass_root points to the root node generated by dtoc.

uclass_root

pointer to head of core tree, if uclasses are in read-only memory and cannot be adjusted to use uclass_root as a list head.

When not in read-only memory, uclass_root_s is used to hold the uclass root, and uclass_root points to the address of uclass_root_s.

dm_driver_rt

Dynamic info about the driver

dm_udevice_rt

Dynamic info about the udevice

dm_priv_base

Base address of the priv/plat region used when udevices and uclasses are in read-only memory. This is NULL if not used

timer

timer instance for Driver Model

fdt_blob

U-Boot’s own device tree, NULL if none

new_fdt

relocated device tree

fdt_size

space reserved for relocated device space

fdt_src

Source of FDT

of_root

root node of the live tree

multi_dtb_fit

pointer to uncompressed multi-dtb FIT image

jt

jump table

The jump table contains pointers to exported functions. A pointer to the jump table is passed to standalone applications.

env_buf

buffer for env_get() before reloc

trace_buff

trace buffer

When tracing function in U-Boot this field points to the buffer recording the function calls.

cur_i2c_bus

currently used I2C bus

timebase_h

high 32 bits of timer

timebase_l

low 32 bits of timer

malloc_start

start of malloc() region

malloc_base

base address of early malloc()

malloc_limit

limit address of early malloc()

malloc_ptr

current address of early malloc()

hose

PCI hose for early use

pci_ram_top

top of region accessible to PCI

pcidelay_done

delay time before scanning of PIC hose expired

If CONFIG_PCI_BOOTDELAY=y, pci_hose_scan() waits for the number of milliseconds defined by environment variable pcidelay before scanning. Once this delay has expired the flag pcidelay_done is set to 1.

cur_serial_dev

current serial device

arch

architecture-specific data

console_out

output buffer for console recording

This buffer is used to collect output during console recording.

console_in

input buffer for console recording

If console recording is activated, this buffer can be used to emulate input.

video_top