How to use --gc-sections?

[Grant Edwards]

I'm stumped: I can't figure out how to discard unused functions
using the -ffunction-sections and --gc-sections options to gcc
and ld.  I know I've gotten it to work in the past with an ARM
target, but now I can't seem to get it to work with an H8
target.

Here's a small example program that illustrates my problem.
After I compile and link test.c, the function named
"functionWeDontUse" should be discarded, but it isn't.

------------------------------test.c------------------------------
int functionWeUse(int i)
{
  return 0x3456 * i;
}

int functionWeDontUse(int i)
{
  return 0x1234 * i;
}

int start(void)
{
  return functionWeUse(75);
}
------------------------------------------------------------------

------------------------------makefile----------------------------
GCC = h8300-elf-gcc -mh
GLD = h8300-elf-ld 
LIBGCC = $(shell $(GCC) -print-libgcc-file-name)

test.elf : test.o test.ld makefile
	$(GLD) -static --gc-sections -Map test.map \
          -T test.ld -o $@ \
          test.o $(LIBGCC)

%.o:	%.c
	$(GCC) -Wall -g -O2 \
          -ffunction-sections -fdata-sections \
          -c $< -o $@

clean:
	rm -f  *.elf *.mot *.map *.o *.o *~
------------------------------------------------------------------

------------------------------test.ld------------------------------
OUTPUT_ARCH(h8300h)
ENTRY(_start)
MEMORY
{
 rom (r)        : o = 0x200000, l = 128k
 ram (rw)       : o = 0x220000, l = 120k
}

SECTIONS
{ 
 .text 0x200100 :
   {
     *(.text.*)
     etext = .; 
   } > rom
   
 .rodata : 
   {
     *(.rodata)
     _erodata = .;
     _mdata = .; 
   } > rom

 .data : AT (_mdata) 
   {
     _data = .;
     *(.data) 
     _edata = .; 
   } > ram

 .bss :
  {
    _bss = . ;
    *(.bss)
    *(COMMON)
     _ebss = . ;
     _end = . ;
  } > ram
}
-------------------------------------------------------------------

$ h8300-elf-gcc -v
Reading specs from /opt/gnu/lib/gcc-lib/h8300-elf/3.3-GNUSH_v0304/specs
Configured with: /home/grante/toolchain/src/gcc-3.3.1-kpit3.04/configure --target=h8300-elf --prefix=/opt/gnu --enable-languages=c --with-gnu-as --with-gnu-ld --with-newlib -v
Thread model: single
gcc version 3.3-GNUSH_v0304

$ h8300-elf-ld -v
GNU ld version GNUSH_v0304 20030612

$ make
h8300-elf-gcc -mh -Wall -g -O2 \
          -ffunction-sections -fdata-sections \
          -c test.c -o test.o
h8300-elf-ld  -static --gc-sections -Map test.map \
          -T test.ld -o test.elf \
          test.o /opt/gnu/lib/gcc-lib/h8300-elf/3.3-GNUSH_v0304/h8300h/libgcc.a

$ file test.elf
test.elf: ELF 32-bit MSB executable, Hitachi H8/300, version 1 (SYSV), statically linked, not stripped

$ nm -a test.elf | grep Dont
00200114 T _functionWeDontUse


$ head -25 test.map

Memory Configuration

Name             Origin             Length             Attributes
rom              0x00200000         0x00020000         r
ram              0x00220000         0x0001e000         rw
*default*        0x00000000         0xffffffff

Linker script and memory map


.text           0x00200100       0x3c
 *(.text.*)
 .text.functionWeUse
                0x00200100       0x14 test.o
                0x00200100                _functionWeUse
 .text.functionWeDontUse
                0x00200114       0x14 test.o
                0x00200114                _functionWeDontUse
 .text.start    0x00200128       0x14 test.o
                0x00200128                _start
                0x0020013c                etext = .

.rodata         0x0020013c        0x0
 *(.rodata)



-- 
Grant Edwards
grante@visi.com

------
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