RE: gcc dead code elimination

Vidar Berg — Thu, 11 Dec 2014 12:05:24 GMT

I tested it here by adding an unused dummy function in the code. Checking the map file afterwards confirmed that it was dumped by the linker. Did you make sure to add the flags to the linker, and not just the compiler?

Example on how to set the flags:

# keep every function in separate section. This will allow linker to dump unused functions
CFLAGS += -ffunction-sections

# let linker to dump unused sections
LDFLAGS := -Wl,--gc-sections

In case you're not aware of it, one trick to easily determine the difference in size of the build is to echo the size. This can be done by adding the following lines to makefile.common:

 #Toolchain commands. Line ~34
SIZE    		:= "$(GNU_INSTALL_ROOT)/bin/$(GNU_PREFIX)-size"

#Line ~141
$(SIZE) $(OUTPUT_BINARY_DIRECTORY)/$(OUTPUT_FILENAME).out