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
NDS32	r10
Nios II	gp
PowerPC	r2
RISC-V	gp (x3)
SuperH	r13
x86 32bit	fs

The sandbox, x86_64, and Xtensa are notable exceptions.

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 defined(CONFIG_LCD) || defined(CONFIG_VIDEO) || defined(CONFIG_DM_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);
  unsigned 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;
#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 defined(CONFIG_SYS_I2C);
  int cur_i2c_bus;
#endif;
  unsigned int timebase_h;
  unsigned int timebase_l;
#if CONFIG_VAL(SYS_MALLOC_F_LEN);
  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;
#ifdef CONFIG_DM_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;
#if CONFIG_IS_ENABLED(WDT);
  struct udevice *watchdog_dev;
#endif;
#ifdef CONFIG_GENERATE_ACPI_TABLE;
  struct acpi_ctx *acpi_ctx;
#endif;
#if CONFIG_IS_ENABLED(GENERATE_SMBIOS_TABLE);
  char *smbios_version;
#endif;
};

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

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

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_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