Segmentation fault using shared object on AIX 5.1

[sdowning at fame dot com (Stuart F. Downing)]

Overview

I am getting a segmentation fault when I run a program linked with a
shared object I generated with gcc.  

Background

gcc -v

reports...
 
Reading specs from /usr/local/lib/gcc-lib/powerpc-ibm-aix5.1.0.0/3.2.2/specs
Configured with: ../gcc-3.2.2/configure --disable-nls
Thread model: aix
gcc version 3.2.2

(I obtained this gcc as a binary distro from http://aixpdslib.seas.ucla.edu)

I compile a source file as follows

gcc -g -pthread -D_LARGE_FILES -c source.c

This is subsequently partially linked into a shared object with other
modules as follows...

gcc -shared -pthread -D_LARGE_FILES -o shared.o source.o other_mod.o other_lib.a -lc -lm -ls

The result is then linked into the main program

gcc -g main.c -o main ./shared.o -lc -lm -ls

When I run the program, I get a segmentation fault just before a
function in source.c is entered, in prologue code that looks like this
(from gdb using stepi)

main () at /vobs/devp/reg/misc/main.c:33
1: x/i $pc  0x10000418 <main+200>:	addi	r3,r1,120
1: x/i $pc  0x1000041c <main+204>:	addi	r4,r1,124
1: x/i $pc  0x10000420 <main+208>:	addi	r5,r1,72
1: x/i $pc  0x10000424 <main+212>:	addi	r6,r1,56
1: x/i $pc  0x10000428 <main+216>:	addi	r7,r1,88
1: x/i $pc  0x1000042c <main+220>:	addi	r8,r1,104
1: x/i $pc  0x10000430 <main+224>:	bl	0x10000570 <cfmopcn>
0x10000570 in cfmopcn ()
1: x/i $pc  0x10000570 <cfmopcn>:	lwz	r12,120(r2)
0x10000574 in cfmopcn ()
1: x/i $pc  0x10000574 <cfmopcn+4>:	stw	r2,20(r1)
0x10000578 in cfmopcn ()
1: x/i $pc  0x10000578 <cfmopcn+8>:	lwz	r0,0(r12)
0x1000057c in cfmopcn ()
1: x/i $pc  0x1000057c <cfmopcn+12>:	lwz	r2,4(r12)
0x10000580 in cfmopcn ()
1: x/i $pc  0x10000580 <cfmopcn+16>:	mtctr	r0
0x10000584 in cfmopcn ()
1: x/i $pc  0x10000584 <cfmopcn+20>:	bctr

Program received signal SIGSEGV, Segmentation fault.
0x00d38f5c in ?? ()
1: x/i $pc  0xd38f5c:	Cannot access memory at address 0xd38f5c
Disabling display 1 to avoid infinite recursion.

using objdump -D I can see that this prolog code is in main, not in
source.o

0000000010000690 <.cfmopcn>:
    10000690:   81 82 00 7c     l       r12,120(r2)
    10000694:   90 41 00 14     st      r2,20(r1)
    10000698:   80 0c 00 00     l       r0,0(r12)
    1000069c:   80 4c 00 04     l       r2,4(r12)
    100006a0:   7c 09 03 a6     mtctr   r0
    100006a4:   4e 80 04 20     bctr
    100006a8:   00 00 00 00     .long 0x0
    100006ac:   00 0c a0 00     .long 0xca000
    100006b0:   00 00 00 00     .long 0x0
    100006b4:   00 00 00 18     .long 0x18

If I compile source.c with the IBM compiler as follows, no
segmentation fault...

cc -qthreaded -D_LARGE_FILES -c source.c

Also, if I link main with the gcc .o's directly, without creating a
shared object, it doesn't seg fault.

Anyone have experience with this?
-- 
Stuart Downing