How to set an absolute load and start address for binary?

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Wed, 2019-04-24 20:04
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hypex
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How to set an absolute load and start address for binary?

Hi guys. ­So I've been experimenting with creating a CFE binary to run things from the CFE firmware. As it turns out, externally it identifies as CFE, but internally CFE uses OpenFirmware.

To run on CFE you just create a standard OS binary but it must be loaded to $200000 and start within this area. So I found some example code from the openbios project. I adapted the ofclient example so it compiled on OS4. 

I made up a makefile that I had working at some stage but somewhere along the line it broke. Now when I load the binary it has a start and entry address of zero! This isn't right and even the binary looks to be set correctly. It doesn't crash but it does hang CFE. My current makefile as follows.

  1. PROGRAM := ofclient
  2. OBJECTS := of1275.o of1275_io.o ofclient.o 
  3. CC      := gcc 
  4. CFLAGS  := -mpowerpc -fpic -fno-builtin-strlen -fno-builtin-exit -Os 
  5. LDFLAGS := -melf32ppc -N -e _start -g -Ttext 0x200000 
  6.  
  7. $(PROGRAM): $(OBJECTS)
  8. 	$(LD) $(LDFLAGS) -Map $(PROGRAM).map -o $(PROGRAM) $(OBJECTS)

Output of relevant info from objdump.

  1. ofclient:     file format elf32-amigaos
  2. ofclient
  3. architecture: powerpc:common, flags 0x00000012:
  4. EXEC_P, HAS_SYMS
  5. start address 0x00200c30
  6.  
  7. Program Header:
  8.     LOAD off    0x00000054 vaddr 0x00200000 paddr 0x00200000 align 2**2
  9.          filesz 0x000010a8 memsz 0x0000130c flags rwx
  10.  
  11. Sections:
  12. Idx Name          Size      VMA       LMA       File off  Algn
  13.   0 .text         00000e9c  00200000  00200000  00000054  2**2
  14.                   CONTENTS, ALLOC, LOAD, CODE
  15.   1 .rodata       00000160  00200e9c  00200e9c  00000ef0  2**2
  16.                   CONTENTS, ALLOC, LOAD, READONLY, DATA
  17.   2 .data         00000002  00200ffc  00200ffc  00001050  2**1
  18.                   CONTENTS, ALLOC, LOAD, DATA
  19.   3 .got          000000a8  00201000  00201000  00001054  2**2
  20.                   CONTENTS, ALLOC, LOAD, CODE
  21.   4 .bss          00000264  002010a8  002010a8  000010fc  2**2
  22.                   ALLOC
  23.   5 .comment      00000081  00000000  00000000  000010fc  2**0
  24.                   CONTENTS, READONLY
  25. SYMBOL TABLE:
  26. 00200000 l    d  .text	00000000 .text
  27. 00200e9c l    d  .rodata	00000000 .rodata
  28. 00200ffc l    d  .data	00000000 .data
  29. 00201000 l    d  .got	00000000 .got
  30. 002010a8 l    d  .bss	00000000 .bss
  31. 00000000 l    d  .comment	00000000 .comment
  32. 00000000 l    df *ABS*	00000000 of1275.c
  33. 00000000 l    df *ABS*	00000000 of1275_io.c
  34. 00000000 l    df *ABS*	00000000 ofclient.c
  35. 0020109c l     O .got	00000000 .hidden _GLOBAL_OFFSET_TABLE_
  36. 00200c30 g     F .text	00000054 _start
  37. 0020130c g       *ABS*	00000000 __end
  38. 00200e00 g     F .text	0000009c main
  39. 002010a8 g       *ABS*	00000000 _edata
  40. 0020130c g       *ABS*	00000000 _end

Comparison with amigaboot.of that works.

  1. architecture: powerpc:common, flags 0x00000012:
  2. EXEC_P, HAS_SYMS
  3. start address 0x00200000
  4.  
  5. Program Header:
  6.     LOAD off    0x00000054 vaddr 0x00200000 paddr 0x00200000 align 2**2
  7.          filesz 0x0000f060 memsz 0x0000f060 flags rwx
  8.  
  9. Sections:
  10. Idx Name          Size      VMA       LMA       File off  Algn
  11.   0 .text         0000c0ec  00200000  00200000  00000054  2**2
  12.                   CONTENTS, ALLOC, LOAD, READONLY, CODE
  13.   1 .rodata       00001048  0020d000  0020d000  0000d054  2**2
  14.                   CONTENTS, ALLOC, LOAD, READONLY, DATA
  15.   2 .data         00000058  0020f000  0020f000  0000f054  2**2
  16.                   CONTENTS, ALLOC, LOAD, DATA
  17.   3 .got2         00000008  0020f058  0020f058  0000f0ac  2**0
  18.                   CONTENTS, ALLOC, LOAD, DATA
  19. SYMBOL TABLE:
  20. 00200000 l    d  .text	00000000 .text
  21. 0020d000 l    d  .rodata	00000000 .rodata
  22. 0020f000 l    d  .data	00000000 .data
  23. 0020f058 l    d  .got2	00000000 .got2
  24. 002039d8 g     F .text	0000015c _start

As you can see there isn't much difference. What would cause it to think the start and load address is zero? And despite having this working what do I need to get it to load at $200000 like I said? I suspect I need a linker script but I didn't need one before. It's kind of annoying when a simle thing like an absolute startign address is complicated to specify. I've read GCC doesn't like to even put the _start routine right at the start and objects must appear in certain order with certain options.

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