nasm externs and macho

Hello all-

I'm trying to understand some weird behavior I'm seeing with nasm on an
Intel Mac.

I have two assembly files, bar.asm and baz.asm. bar references labels
defined by baz. But it doesn't seem like the object files are being
linked together properly, unless I am misinterpreting what gdb is
printing and what my C code is doing. In particular, the references in
the data of bar do not correspond to the actual addresses of the data
in baz.

Perhaps I have misunderstood something about the macho format or about
the Mac OS X ABI. Does dynamic linking get in the way of doing this
sort of resolution of addresses in the data section?

I have replicated a simpler version of the problem with four files (the
two assembly files, some C code to print out the bad values, and a
Makefile to build it all and print the output to a text file).
I have copied the four files below, along with the output that is
printed to problem.txt. The key problem is that &baz is determined by
the C code to be 0x00002024, but the entry in the bar array
corresponding to the label for baz is the number 0x00001cdf.

Does anyone have an idea why this might be happening, and whether the
problem is in the OS X linker (unlikely), Nasm's mach-o support, or in
my mental model of how the two assembly files should be linking
together?

;;; baz.asm
section .data
align 8
global _baz
_baz:
dd 0xdeadbead
;;; end of baz.asm

;;; bar.asm
section .data
align 8
global _bar
extern _foo
extern _foil
extern _baz
_bar:
dd 0x12345678
dd _foo
dd _foil
dd _baz
dd _bar

;;; end of bar.asm

/* foo.c */
#include <stdio.h>

int foiled(int x) { return 4*x + 7; }

int foil(int x) { return 3*x + 2; }

int foo(int x) { return 2*x + 1; }

extern int *bar;
extern int *baz;

int main() {
printf(" &foil: 0x%08x\n", &foil);
printf(" &foo: 0x%08x\n", &foo);
printf(" bar: 0x%08x\n", bar);
printf(" &bar: 0x%08x\n", &bar);
printf(" baz: 0x%08x\n", baz);
printf(" &baz: 0x%08x\n", &baz);
printf(" (&bar)[0] 0x12345678: 0x%08x\n", (&bar)[0]);
printf(" (&bar)[1] _foo : 0x%08x\n", (&bar)[1]);
printf(" (&bar)[2] _foil : 0x%08x\n", (&bar)[2]);
printf(" (&bar)[3] _baz : 0x%08x\n", (&bar)[3]);
printf(" (&bar)[4] _bar : 0x%08x\n", (&bar)[4]);
return 0;
}
/* end of foo.c */

# Makefile
problem.txt: foo
echo problem.txt > problem.txt
nasm -v >> problem.txt
./foo >> problem.txt
echo end of problem.txt >> problem.txt

foo: foo.c bar.o baz.o
gcc -o foo foo.c bar.o baz.o

bar.o: bar.asm
nasm -f macho bar.asm

baz.o: baz.asm
nasm -f macho baz.asm
# End of Makefile

problem.txt
NASM version 0.98.40 (Apple Computer, Inc. build 9) compiled on Apr 6
2006
&foil: 0x00001cdf
&foo: 0x00001cf3
bar: 0x12345678
&bar: 0x00002010
baz: 0xdeadbead
&baz: 0x00002024
(&bar)[0] 0x12345678: 0x12345678
(&bar)[1] _foo : 0x00001cf3
(&bar)[2] _foil : 0x00001cdf
(&bar)[3] _baz : 0x00001cdf
(&bar)[4] _bar : 0x00002010
end of problem.txt

.

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