How can I modify vmlinux.lds to break up a built-in.o? - linux

Question

So I'm working with ucLinux under the NXP LPC1788 processor (ARM-CortexM3, no MMU). The ucLinux port was orignally done by Emcraft Systems.
The 1788 has 512KiB of onboard flash (called eNVM) which is faster to access than the rest of memory connected via the external memory controller. Emcraft's linker script has a portion where you can relocate critical parts of the kernel to this eNVM area. I'm using 80K for the bootloader so I have 432K free to stuff with as much kernel as I can.
So the linker script, vmlinux.lds.S, has a portion that begins like this:
#ifdef CONFIG_KERNEL_IN_ENVM
_envm_loc = .;
.envm ENVM_PHYS_OFFSET + CONFIG_KERNEL_IN_ENVM_OFFSET * 1024 : {
_envm_start = .;
#if CONFIG_KERNEL_IN_ENVM_SIZE>0
__exception_text_start = .;
*(.exception.text*)
*(.exception.rodata*)
__exception_text_end = .;
SCHED_TEXT
LOCK_TEXT
KPROBES_TEXT
usr/built-in.o(.text)
usr/built-in.o(.rodata*)
init/built-in.o(.text)
init/built-in.o(.rodata*)
mm/built-in.o(.text)
mm/built-in.o(.rodata*)
...and so on. As you can see, entire subdirectories are being pulled in via their built-in.o object file.
As I get closer and closer to the end of the flash space, I'd like to have a bit more control over what gets linked here. drivers/built-in.o, for example, won't fit in the free space but if I could get drivers/usb and drivers/input here, that would help a lot.
If I modify the linker script to have just those portions, like this:
drivers/usb/built-in.o(.text)
drivers/usb/built-in.o(.rodata*)
drivers/input/built-in.o(.text)
drivers/input/built-in.o(.rodata*)
then I get duplicate symbol errors when drivers/built-in.o gets linked. I can't see where that happens exactly, so that's part of the problem I think.
So the question: Is there a way to link individual built-in.o files to different regions without linking the master .o built at the top of the directory?
I've put the whole linker file at http://pastebin.com/qcj6rHme if anyone wants to take a look.
Thanks!

Answer 1

If you're going to link usb and input directly, drivers/built-in.o should not include them. Modifying Kbuild to build the subdirs but not include them is a bit tricky; those two elements will have to filtered out of obj-y where drivers/built-in.o is generated -- if they aren't included in obj-y they won't get built at all.