meminfo command

Synopsis

meminfo

Description

The meminfo command shows the amount of memory. If CONFIG_CMD_MEMINFO_MAP is enabled, then it also shows the layout of memory used by U-Boot and the region which is free for use by images. In architectures that support it, it also prints the mapped pages and their permissions. The latter is architecture specific.

The layout of memory is set up before relocation, within the init sequence in board_init_f(), specifically the various reserve_...() functions. This ‘reservation’ of memory starts from the top of RAM and proceeds downwards, ending with the stack. This results in the maximum possible amount of memory being left free for image-loading.

The meminfo command writes the DRAM size. If the architecture also supports it, page table entries will be shown next. Finally the rest of the outputs are printed in 5 columns:

Region: Name of the region
Base: Base address of the region, i.e. where it starts in memory
Size: Size of the region, which may be a little smaller than the actual size reserved, e.g. due to alignment
End: End of the region. The last byte of the region is one lower than the address shown here
Gap: Gap between the end of this region and the base of the one above

Regions shown are:

video: Memory reserved for video framebuffers. This reservation happens in the bind() methods of all video drivers which are present before relocation, so the size depends on that maximum amount of memory which all such drivers want to reserve. This may be significantly greater than the amount actually needed, if the display is ultimately set to a smaller resolution or colour depth than the maximum supported.
code: U-Boot’s code and Block-Starting Symbol (BSS) region. Before relocation, U-Boot copies its code to a high region and sets up a BSS immediately after that. The size of this region is generally therefore __bss_end - __image_copy_start
malloc: Contains the malloc() heap. The size of this is set by CONFIG_SYS_MALLOC_LEN.
board_info: Contains the bd_info structure, with some information about the current board.
global_data: Contains the global-data structure, pointed to by gd. This includes various pointers, values and flags which control U-Boot.
devicetree: Contains the flatted devicetree blob (FDT) being used by U-Boot to configure itself and its devices.
bootstage: Contains the bootstage records, which keep track of boot time as U-Boot executes. The size of this is determined by CONFIG_BOOTSTAGE_RECORD_COUNT, with each record taking approximately 32 bytes.
bloblist: Contains the bloblist, which is a list of tables and other data created by U-Boot while executed. The size of this is determined by CONFIG_BLOBLIST_SIZE.
stack: Contains U-Boot’s stack, growing downwards from the top. The nominal size of this region is set by CONFIG_STACK_SIZE but there is no actual limit enforced, so the stack can grow behind that. Images should be loaded lower in memory to avoid any conflict.
free: Free memory, which is available for loading images. The base address of this is gd->ram_base which is generally set by CFG_SYS_SDRAM_BASE.

Aarch64 specific flags

More information on the output can be found Chapter D8 - The AArch64 Virtual Memory System Architecture at https://developer.arm.com/documentation/ddi0487/latest/

In short, for a stage 1 translation regime the following apply:

RWX: Pages mapped with Read, Write and Execute permissions
RO: Pages mapped with Read-Only permissions
PXN: PXN (Privileged Execute Never) applies to execution at EL1 and above
UXN: UXN (Unprivileged Execute Never) applies to EL0

Example

This example shows output with both CONFIG_CMD_MEMINFO and CONFIG_CMD_MEMINFO_MAP enabled for aarch64 qemu:

DRAM:  8 GiB
Walking pagetable at 000000023ffe0000, va_bits: 40. Using 4 levels
[0x0000023ffe1000]                          |  Table |            |               |
  [0x0000023ffe2000]                        |  Table |            |               |
    [0x00000000000000 - 0x00000008000000]   |  Block | RWX        | Normal        | Inner-shareable
    [0x00000008000000 - 0x00000040000000]   |  Block | PXN UXN    | Device-nGnRnE | Non-shareable
  [0x00000040000000 - 0x00000200000000]     |  Block | RWX        | Normal        | Inner-shareable
  [0x0000023ffea000]                        |  Table |            |               |
    [0x00000200000000 - 0x0000023f600000]   |  Block | RWX        | Normal        | Inner-shareable
    [0x0000023ffeb000]                      |  Table |            |               |
      [0x0000023f600000 - 0x0000023f68c000] |  Pages | RWX        | Normal        | Inner-shareable
      [0x0000023f68c000 - 0x0000023f74f000] |  Pages | RO         | Normal        | Inner-shareable
      [0x0000023f74f000 - 0x0000023f794000] |  Pages | PXN UXN RO | Normal        | Inner-shareable
      [0x0000023f794000 - 0x0000023f79d000] |  Pages | PXN UXN    | Normal        | Inner-shareable
      [0x0000023f79d000 - 0x0000023f800000] |  Pages | RWX        | Normal        | Inner-shareable
    [0x0000023f800000 - 0x00000240000000]   |  Block | RWX        | Normal        | Inner-shareable
  [0x00000240000000 - 0x00004000000000]     |  Block | RWX        | Normal        | Inner-shareable
  [0x0000023ffe3000]                        |  Table |            |               |
    [0x00004010000000 - 0x00004020000000]   |  Block | PXN UXN    | Device-nGnRnE | Non-shareable
[0x0000023ffe4000]                          |  Table |            |               |
  [0x00008000000000 - 0x00010000000000]     |  Block | PXN UXN    | Device-nGnRnE | Non-shareable

Region           Base     Size      End      Gap
------------------------------------------------
video        23f7e0000   800000 23ffe0000
code         23f68a000   156000 23f7e0000        0
malloc       23e64a000  1040000 23f68a000        0
board_info   23e649f80       78 23e649ff8        8
global_data  23e649df0      188 23e649f78        8
devicetree   23e549df0   100000 23e649df0        0
bloblist     23e547000     2000 23e549000      df0
stack        23d546ff0  1000000 23e546ff0       10
lmb          23d546ff0        0 23d546ff0        0
lmb          23d543000     3ff0 23d546ff0        0
free         40000000 23d543000 27d543000 ffffffffc0000000

Return value

The return value $? is always 0 (true).