Re: Undetected duplicate symbols

[Marius Groeger <mgroeger at sysgo dot com>]

On Tue, 7 Feb 2006, Khem Raj wrote:

> Do you have your own linker script file ? or do you use default one. I think 
> you need to have your own for the system
> either way you can remove the symbol for linker script and see if that works. 
> Would be nice if you could make a short example to exhibit the problem.

Sure, see below.

Writing this example I found the issue not only happens with my MIPS
toolchain, but also with my host gcc. Most convincing is the disassembly; it
clearly shows that the _start which I defined as entry point is has been
lost. Maybe it's a "feature" that linker script variables override
application variables, but don't think I like this feature then...

  sh# gcc -c -o duplicate.o duplicate.c
  sh# ld -o duplicate -T duplicate-ld duplicate.o
  sh# nm duplicate
  00000000 T dummy
  00000000 T _start
  mag@mag:~/work> nm duplicate.o
  00000000 T dummy
  00000025 T _start
  mag@mag:~/work> objdump -d duplicate

  duplicate:     file format elf32-i386

  Disassembly of section .text:

  00000000 <_start>:
     0:   55                      push   %ebp
     1:   89 e5                   mov    %esp,%ebp
     3:   83 ec 04                sub    $0x4,%esp
     6:   c7 45 fc 00 00 00 00    movl   $0x0,0xfffffffc(%ebp)
     d:   8b 45 fc                mov    0xfffffffc(%ebp),%eax
    10:   83 f8 63                cmp    $0x63,%eax
    13:   7e 02                   jle    17 <_start+0x17>
    15:   eb 09                   jmp    20 <_start+0x20>
    17:   8b 45 fc                mov    0xfffffffc(%ebp),%eax
    1a:   40                      inc    %eax
    1b:   89 45 fc                mov    %eax,0xfffffffc(%ebp)
    1e:   eb ed                   jmp    d <_start+0xd>
    20:   8b 45 fc                mov    0xfffffffc(%ebp),%eax
    23:   c9                      leave
    24:   c3                      ret
    25:   55                      push   %ebp
    26:   89 e5                   mov    %esp,%ebp
    28:   83 ec 08                sub    $0x8,%esp
    2b:   c7 45 fc 00 00 0c bf    movl   $0xbf0c0000,0xfffffffc(%ebp)
    32:   e8 c9 ff ff ff          call   0 <_start>
    37:   89 c2                   mov    %eax,%edx
    39:   8b 45 fc                mov    0xfffffffc(%ebp),%eax
    3c:   89 10                   mov    %edx,(%eax)
    3e:   c9                      leave
    3f:   c3                      ret



Sampel application "duplicate.c":
  extern int dummy(void)
  {
      volatile int i;

      /* create some .text data to move _start away from the beginning */

      for(i = 0; i < 100; i++)
          ;

      return i;
  }

  extern void _start(void)
  {
      volatile int *p = (volatile int*)0xbf0c0000;

      *p = dummy();
  }

Linker script "duplicate-ld":
  SECTIONS
  {
      .text 0x00000000:
      {
          _start = . ;
          *(.text)
      }
  }

Marius

--
Marius Groeger <mgroeger@sysgo.com>
SYSGO AG                      Embedded and Real-Time Software
Voice: +49 6136 9948 0                  FAX: +49 6136 9948 10
www.sysgo.com | www.elinos.com | www.osek.de | www.pikeos.com


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