Commands are added to U-Boot by creating a new command structure.
-This is done by first including command.h
-
-Then using the U_BOOT_CMD() macro to fill in a cmd_tbl_t struct.
+This is done by first including command.h, then using the U_BOOT_CMD() macro
+to fill in a cmd_tbl_t struct.
U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")
name: is the name of the commad. THIS IS NOT a string.
-maxargs: the maximumn numbers of arguments this function takes
+maxargs: the maximum number of arguments this function takes
+repeatable: either 0 or 1 to indicate if autorepeat is allowed
command: Function pointer (*cmd)(struct cmd_tbl_s *, int, int, char *[]);
usage: Short description. This is a string
-help: long description. This is a string
+help: Long description. This is a string
-**** Behinde the scene ******
+**** Behind the scene ******
-The structure created is named with a special prefix (__u_boot_cmd_)
+The structure created is named with a special prefix (__u_boot_list_cmd_)
and placed by the linker in a special section.
This makes it possible for the final link to extract all commands
compiled into any object code and construct a static array so the
-command can be found in an array starting at __u_boot_cmd_start.
+command can be found in an array starting at _u_boot_list_cmd__start.
+
+To ensure that the linker does not discard these symbols when linking
+full U-Boot we generate a list of all the commands we have built (based
+on the sections mentioned above) and use that to force the linker to
+first enter the symbol as undefined in the output object so that there
+is then a need for the symbol to be kept (this is the UNDEF_SYM logic in
+the Makefile).
If a new board is defined do not forget to define the command section
by writing in u-boot.lds ($(TOPDIR)/board/boardname/u-boot.lds) these
3 lines:
- __u_boot_cmd_start = .;
- .u_boot_cmd : { *(.u_boot_cmd) }
- __u_boot_cmd_end = .;
+ .u_boot_list : {
+ #include "u-boot.lst";
+ }