RE: Resolving External References

["Savithri Venkatachalapathy, Noida" <savithriv at noida dot hcltech dot com>]

Hello Nick,

These are the details.
    
  * What host are you running on ?
	I am running on sparc machine.

  * What version of binutils are you using ? What target are the binutils
targeted at, (if it is different from
    your host) ?
    I am using  Algor MIPS cross-compler, release 4.0c ( SDE-MIPS )

  * What command line did you use in order to link together a.o and
    b.o ?
Source files: 
-------------
fun1.c 
           int myfunc() 
           {
             int  x = foo(); 
           }
fun2.c
           int x = 15;
           int foo()
           {
             return x;
           } 

           int main() 
           {
             foo(); 
             exit(0);
           }

Commands:
---------

    gcc -c -EL  -fpic -o a.o fun1.c 
    gcc -c -EL  -fpic -o b.o fun2.c 
    ld -verbose -i  -EL -fpic -o mytest.elf -defsym __start=0xbfc00000
-Tmyapp_lnk a.o b.o
  
Linker script(myapp_lnk): 
-------------------------

    OUTPUT_FORMAT("elf32-littlemips")
    SECTIONS
    {
       .BOOT 0xbfc00000 : {
                            a.o 
                          }

       .RUN 0x80002000 : { 
			          b.o 
                         }
    }

  * What address does object show for the reference to foo() from a.o
    ?  What address should it be ?
 
Executable file:
----------------
mytest.elf:     file format elf32-littlemips

Disassembly of section .BOOT:

bfc00000 <myfunc>:
bfc00000:	27bdffe0 	addiu	$sp,$sp,-32
bfc00004:	afbf001c 	sw	$ra,28($sp)
bfc00008:	afbe0018 	sw	$s8,24($sp)
bfc0000c:	0c000000 	jal	b0000000 <x+0x2fffdfa4>
bfc00010:	03a0f025 	move	$s8,$sp
bfc00014:	afc20010 	sw	$v0,16($s8)
bfc00018:	03c0e825 	move	$sp,$s8
bfc0001c:	8fbf001c 	lw	$ra,28($sp)
bfc00020:	8fbe0018 	lw	$s8,24($sp)
bfc00024:	03e00008 	jr	$ra
bfc00028:	27bd0020 	addiu	$sp,$sp,32
bfc0002c:	e0000004 	swc0	$0,4($zero)
	...
Disassembly of section .RUN:

80002000 <foo>:
80002000:	27bdfff8 	addiu	$sp,$sp,-8
80002004:	afbe0000 	sw	$s8,0($sp)
80002008:	03a0f025 	move	$s8,$sp
8000200c:	8f83806d 	lw	$v1,-32659($gp)
80002010:	00000000 	nop
80002014:	10000001 	b	8000201c <foo+0x1c>
80002018:	00601025 	move	$v0,$v1
8000201c:	03c0e825 	move	$sp,$s8
80002020:	8fbe0000 	lw	$s8,0($sp)
80002024:	03e00008 	jr	$ra
80002028:	27bd0008 	addiu	$sp,$sp,8

8000202c <main>:
8000202c:	27bdffe8 	addiu	$sp,$sp,-24
80002030:	afbf0014 	sw	$ra,20($sp)
80002034:	afbe0010 	sw	$s8,16($sp)
80002038:	0c000000 	jal	80000000 <foo-0x2000>
8000203c:	03a0f025 	move	$s8,$sp
80002040:	0c000000 	jal	80000000 <foo-0x2000>
80002044:	00002025 	move	$a0,$zero
80002048:	03c0e825 	move	$sp,$s8
8000204c:	8fbf0014 	lw	$ra,20($sp)
80002050:	8fbe0010 	lw	$s8,16($sp)
80002054:	03e00008 	jr	$ra
80002058:	27bd0018 	addiu	$sp,$sp,24

8000205c <x>:
8000205c:	0000000f 	0xf

The function foo() has been relocated to address 80002000 in the executable
mytest.elf
Hence the reference to foo() from a.o should show the address 80002000.
But it is showing the address  b0000000 <x+0x2fffdfa4>.

'x' is a global constant set to 0x0f in the object file b.o and 
is relocated in the executable mytest.elf to  8000205c
       

  * Does the linked program work, despite the apparent discrepancy in
    addresses ?
    No, foo() never gets executed..

  * Do you have a *small* example that reproduces the problem ?
    Given above :)

    
Thanks,
savi

-----Original Message-----
From: Nick Clifton [mailto:nickc at redhat dot com]
Sent: Wednesday, March 26, 2003 6:09 PM
To: Savithri Venkatachalapathy, Noida
Cc: binutils at sources dot redhat dot com; Rishabh Gupta, Noida;
binutils at sourceware dot cygnus dot com
Subject: Re: Resolving External References


Hi Savithri,

> I am using "ld" command to link 2 object files a.o and b.o
> a.o has an external reference to function foo() defined in b.o
> 
> When I look at the objdump, it has resolved the external reference to
> different address rather than that of foo().

Please could you provide more information about your problem.  In
particular:

  * What version of binutils are you using ?

  * What host are you running on ?

  * What target are the binutils targeted at, (if it is different from
    your host) ?

  * What command line did you use in order to link together a.o and
    b.o ?

  * What address does object show for the reference to foo() from a.o
    ?  What address should it be ?

  * Does the linked program work, despite the apparent discrepancy in
    addresses ?

  * Do you have a *small* example that reproduces the problem ?

Cheers
        Nick