README.commands: Document what UNDEF_SYM does
Changes in v2:
- Reword a bit more
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/doc/README.commands b/doc/README.commands
index 27815d2..125f077 100644
--- a/doc/README.commands
+++ b/doc/README.commands
@@ -22,6 +22,13 @@
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.
+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: