The compiler uses the feedback file generated by the linker to compile the source code in
a way that enables the linker to subsequently discard the unused functions.
To obtain maximum benefit from linker feedback, do a full compile and link at least
twice. A single compile and link using feedback from a previous build is normally
sufficient to obtain some benefit.
Always ensure that you perform a full clean build immediately prior to using the linker
feedback file. This minimizes the risk of the feedback file becoming out of date with
the source code it was generated from.
You can specify the
--feedback= option even
when no feedback file exists. This enables you to use the same build commands or makefile
regardless of whether a feedback file exists, for example:
armcc -c --feedback=unused.txt test.c -o test.o
armlink --feedback=unused.txt test.o -o test.axf
The first time you build the application, it compiles normally but the compiler warns you
that it cannot read the specified feedback file because it does not exist. The link
command then creates the feedback file and builds the image. Each subsequent compilation
step uses the feedback file from the previous link step to remove any unused functions
that are identified.