A large chunk of U-Boot's executable size is the code to process and execute commands. This is reasonable, since commands and scripts are an important part of U-Boot's feature set and provide much of its flexibility.
However, for some applications only a very limited set of commands is required. Where image size is important, it is desirable to be able to easily remove unwanted code.
This series introduces a new board_run_command() function which can be used to run a small subset of commands as required by the board (typically load and bootm), thus allowing the rest of the commands to be automatically and reliably dropped from the image using toolchain dead code elimination.
Tests on snow (ARMv7) show this reduces image size dramatically, more than just undefining all the commands:
text data bss dec hex filename before: 356359 12550 300056 668965 a3525 b/snow/u-boot with all commands undefined: 155336 5402 8624 169362 29592 b/snow/u-boot with this series: 123177 2958 1544 127679 1f2bf b/snow/u-boot
The difference is more pronounced the more effort is put into reducing the image size. For example, removing additional subsystem options yields:
text data bss dec hex filename with all commands undefined and most subsystems: 86479 4186 7480 98145 17f61 b/snow/u-boot with this series: 52395 1818 228 54441 d4a9 b/snow/u-boot
Further, it is possible to enable some of the split-use options like CONFIG_CMD_USB, and get USB support without the unwanted command overhead (it would be better if USB had a separate option for the command and the USB stack, but that is not the case, and a few other features have a similar problem).
U-Boot can then become a really minimal boot loader, with only the required functions available. Simply undefining various unwanted commands in the board config is not as effective, and is much more time-consuming to figure out. Apart from the cost of the parsing code, the commands necessarily provide a lot options and features which are not required by many boards.
In particular, with this series, it is possible to run a minimal U-Boot within the SRAM of a modern SoC, providing the benefits of the full U-Boot environment with the small size of SPL. This helps to bridge the gap somewhat. A key difference between U-Boot and SPL is the inclusion of the command parser, and this small size of SPL is a key reason why some boards currently use 'falcon mode', where only SPL is used to boot a kernel.
This series has a fairly small impact on the source code, changing command.h and a fairly small change to each list of subcommands (there are about 19 such sites in U-Boot).
Note: some effort was expended in trying to obtain the same result with just linker code elimination. However this did not work, since the linker would not eliminate some transitively-called functions like do_fdt() even when callers are removed.
Simon Glass (6): Add an info word to commands Refactor command macros so they can compile to nothing Add CONFIG_CMDLINE to allow removal of all commands main: Exclude getline code when CONFIG_CMDLINE is not defined main: Process FDT options even without CONFIG_BOOTDELAY sandbox: Add board_run_command() function
README | 8 +++ arch/x86/cpu/u-boot.lds | 4 ++ board/inka4x0/inkadiag.c | 12 ++-- board/intercontrol/digsy_mtc/cmd_mtc.c | 20 +++---- board/sandbox/sandbox/sandbox.c | 10 ++++ common/cmd_bmp.c | 8 +-- common/cmd_bootm.c | 39 ++++++++----- common/cmd_bootstage.c | 10 ++-- common/cmd_cbfs.c | 3 +- common/cmd_clk.c | 6 +- common/cmd_demo.c | 10 ++-- common/cmd_help.c | 4 ++ common/cmd_i2c.c | 34 +++++------ common/cmd_nvedit.c | 42 +++++++------- common/cmd_onenand.c | 23 ++++---- common/cmd_pxe.c | 6 +- common/cmd_sandbox.c | 14 ++--- common/cmd_sound.c | 8 +-- common/cmd_spl.c | 14 ++--- common/cmd_tpm.c | 52 ++++++++--------- common/command.c | 12 +++- common/main.c | 101 ++++++++++++++++++++++---------- drivers/gpio/pca953x.c | 14 ++--- drivers/gpio/tca642x.c | 14 ++--- drivers/misc/ds4510.c | 24 ++++---- include/command.h | 102 ++++++++++++++++++++++++++++----- include/config_defaults.h | 2 + include/config_fallbacks.h | 7 +++ test/dm/cmd_dm.c | 10 ++-- 29 files changed, 392 insertions(+), 221 deletions(-)