Proper way of using link time opimization with source and assembly files?

Question

I'm currently playing around with LTO for an embedded system (to see if it could reduce the size) and was having some issues getting everything to link properly using ld directly and was wondering what I was doing wrong. This is mostly playing with a toy program before I use this in a larger project.

The setup is basically I have 3 files:

• test.c - data transform function
• test_main.c - calls a function defined in start.S
• start.S - calls a function in test.c and also contains _start

I compile the files using:

arm-none-eabi-as -mthumb -Wall start.S -o start.o
arm-none-eabi-gcc -Wall -Werror -march=armv7 -mtune=cortex-r7 -mthumb -fPIC -nostdlib -flto -static test.c -c test.o
arm-none-eabi-gcc -Wall -Werror -march=armv7 -mtune=cortex-r7 -mthumb -fPIC -nostdlib -flto -static test_main.c -c test_main.o

If I then try to link the program with ld I get:

arm-none-eabi-ld --static -fPIC --shared --fatal-warning test.o start.o test_main.o -test
arm-none-eabi-ld: test.o: plugin needed to handle lto object
arm-none-eabi-ld: test.o: plugin needed to handle lto object
arm-none-eabi-ld: test_main.o: plugin needed to handle lto object
arm-none-eabi-ld: test_main.o: plugin needed to handle lto object   

If I use gcc though, it works:

arm-none-eabi-gcc -Wall -Werror -march=armv7 -mtune=cortex-r7 -mthumb -fPIC -nostdlib -flto -static test.o start.o test_main.o -o test.gcc

I have tried specifying the linker plugin directly but then I get a different error:

arm-none-eabi-ld --static -fPIC --shared --fatal-warning --plugin <path_to_correct>/liblto_plugin.so test.o start.o test_main.o -test
arm-none-eabi-ld: <path_to_correct>.../lto-plugin.c:741: all_symbols_read_handler: Assertion 'lto_wrapper_argv' failed.
Aborted (core dumped)

What flags, parameters, etc. am I missing in my ld call?