Partial Linking

[Ian Broster]

Is there any reason why when partial linking with ld -r that
local symbols cannot be completely resolved and therefore
removed from the symbol table?

It seems that a link with ld -r still requires the local
symbols to be kept; only on the final link to produce
a static executable are the local symbols finally
resolved. For example, following the symbol p1 through
the process below.

Thanks for any insight!
Ian



% cc    -c -o a.o a.c
% nm a.o
00000044 T global
00000000 T main
0000002c T p1
         U p2
         U printf
% # p1 is global, but not really need beyond this [group of] file[s].
% # Make p1 local
% objcopy -L p1 a.o
% # Partial link
% ld -r -o a1.o a.o
% # Have a look at the symbol table; p1 is local.
% nm a1.o
00000044 T global
00000000 T main
0000002c t p1
         U p2
         U printf
% # But the code still requires the symbol, see address 0x20:

objdump -d a1.o         

a1.o:     file format elf32-i386

Disassembly of section .text:

00000000 <main>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 ec 08                sub    $0x8,%esp
   6:   83 e4 f0                and    $0xfffffff0,%esp
   9:   b8 00 00 00 00          mov    $0x0,%eax
   e:   29 c4                   sub    %eax,%esp
  10:   83 ec 0c                sub    $0xc,%esp
  13:   68 00 00 00 00          push   $0x0
  18:   e8 fc ff ff ff          call   19 <main+0x19>
  1d:   83 c4 10                add    $0x10,%esp
  20:   e8 fc ff ff ff          call   21 <main+0x21>
  25:   e8 fc ff ff ff          call   26 <main+0x26>
  2a:   c9                      leave
  2b:   c3                      ret

0000002c <p1>:
  2c:   55                      push   %ebp
  2d:   89 e5                   mov    %esp,%ebp
  2f:   83 ec 08                sub    $0x8,%esp
  32:   83 ec 0c                sub    $0xc,%esp
  35:   68 06 00 00 00          push   $0x6
  3a:   e8 fc ff ff ff          call   3b <p1+0xf>
  3f:   83 c4 10                add    $0x10,%esp
  42:   c9                      leave
  43:   c3                      ret

00000044 <global>:
  44:   55                      push   %ebp
  45:   89 e5                   mov    %esp,%ebp
  47:   83 ec 08                sub    $0x8,%esp
  4a:   83 ec 0c                sub    $0xc,%esp
  4d:   68 0a 00 00 00          push   $0xa
  52:   e8 fc ff ff ff          call   53 <global+0xf>
  57:   83 c4 10                add    $0x10,%esp
  5a:   c9                      leave
  5b:   c3                      ret

% Indeed, we cannot remove it.
% objcopy -N p1 a1.o big.o
BFD: big.o: symbol `p1' required but not present
objcopy: big.o: No symbols