objcopy elf32-i386 to pe-i386 breaks R_386_32 relocations

[Dave Denholm]

Hi,
   I think there's a bug in the way objcopy handles R_386_32 (absolute
32-bit) relocation entries when translating from elf to pe-i386
(windows) object files.

I first found it running cygwin objcopy on windows, and reproduced it
on linux.

cygwin version is

E:\>c:\cygwin\bin\objcopy --version
GNU objcopy 2.16.91 20050610

linux version is
$ objcopy --version
GNU objcopy (GNU Binutils) 2.18.0.20080103
Copyright 2007 Free Software Foundation, Inc.

(freshly downloaded, and bfd configured with all targets)



The symptom is that R_386_32 relocations in elf get translated into
DIR16 entries in the pe-i386. (Or perhaps just not translated, since I
think DIR16 is numerical value 1, which I think is the same numerical
value as R_386_REL, and possibly also the same value as bfd uses
internally, though that part is pure speculation from a very quick
look at the source.)


Consider

$ cat test.c

extern int e;
int *p = &e;

$ gcc -c test.c

$ objdump -r test.o

test.o:     file format elf32-i386

RELOCATION RECORDS FOR [.data]:
OFFSET   TYPE              VALUE 
00000000 R_386_32          e


$ objcopy -O pe-i386 test.o test.obj

$ objdump -r -b pe-i386 test.obj

test.obj:     file format pe-i386

RELOCATION RECORDS FOR [.data]:
OFFSET   TYPE              VALUE 
00000000 1                 e


# then try to convert back :

$ objcopy -I pe-i386 -O elf32-i386 test.obj back-again.o
BFD: back-again.o: unsupported relocation type (null)
./binutils_gen/binutils/objcopy: back-again.o: Bad value



Running dumpbin on windows on test.obj gives

E:\>dumpbin /relocations z:\tmp\test.obj
Microsoft (R) COFF Binary File Dumper Version 6.00.8168
Copyright (C) Microsoft Corp 1992-1998. All rights reserved.


Dump of file z:\tmp\test.obj

File Type: COFF OBJECT

RELOCATIONS #2
                                                Symbol    Symbol
 Offset    Type              Applied To         Index     Name
 --------  ----------------  -----------------  --------  ------
 00000000  DIR16                          0000         1  e

  Summary

           0 .bss
          23 .comment
           4 .data
           0 .note.GNU-stack
           0 .text



(and ms linker rejects the fixup entries as invalid if I try to use
such a converted file...)


dd
-- 
Dave Denholm              <address@hidden>       http://www.esmertec.com