Date: Thu, 12 Feb 2004 12:46:10 -0800 (PST) From: Adam Bozanich <abozan01@ccsf.edu> To: freebsd-questions@freebsd.org Subject: nasm, ld, libc, and **environ Message-ID: <Pine.HPX.4.44.0402121239450.5390-100000@hills.ccsf.cc.ca.us>
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Hi all. I am trying to learn asm with NASM on a FreeBSD system. I really
need to debug my programs while I learn, so I want to use printf. This is
what I am using to assemble and link:
nasm -f elf use_printf.asm
ld -o use_printf use_printf.asm -lc
but then when I run the program:
$./use_printf
/usr/libexec/ld-elf.so.1: /lib/libc.so.5: Undefined symbol "environ"
If I try to use static linking, I get this:
$ld -static -o use_printf use_printf.asm -lc
/usr/lib/libc.a(getenv.o): In function `getenv':
getenv.o(.text+0x19): undefined reference to `environ'
getenv.o(.text+0x29): undefined reference to `environ'
getenv.o(.text+0x63): undefined reference to `environ'
/usr/lib/libc.a(getenv.o): In function `__findenv':
getenv.o(.text+0xd5): undefined reference to `environ'
getenv.o(.text+0xe2): undefined reference to `environ'
/usr/lib/libc.a(getenv.o)(.text+0x113): more undefined references to `environ' follow
/usr/lib/libc.a(getprogname.o): In function `_getprogname':
getprogname.o(.text+0x4): undefined reference to `__progname'
Can somebody see where I am going wrong? This is kindof holding me back. I
added the 'extern environ' and 'extern __progname' beause I get this otherwise:
(when NOT using -static)
/usr/lib/libc.so: undefined reference to `environ'
/usr/lib/libc.so: undefined reference to `__progname'
Here's what I have:
;;;;;;;;;;;;;;;;;;;;;; BEGIN CODE ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
extern printf
extern environ
extern __progname
section .data
mesg db 'the number is %d\n',0
mesglen equ $-mesg
errormesg db 'libc error',0ah,0
errormesglen equ $-errormesg
newline db 10
number dw 0x10
kernel:
int 80h
ret
align 4
section .text
global _start
_start:
; call printf from libc
push dword number
push dword mesg
call printf
; error if eax < 1 ( we should have wrote some chars )
cmp eax , 0x1
jl .error
; use write() system call to print message
push dword mesglen
push dword mesg
push dword 0x1 ; stdout
mov eax , 0x4 ; 4 == write system call
call kernel
; output a newline
push dword 1
push dword newline
push dword 0x1
mov eax , 0x4
call kernel
mov eax , 0x1 ; exit syscall number
push dword 0x0 ; exit status
call kernel
.error:
push dword errormesglen
push dword errormesg
push dword 0x1
mov eax , 0x4
call kernel
mov eax , 0x1
push dword 0xff
call kernel
;;;;;;;;;;;;;;;; END CODE ;;;;;;;;;;;;;;;;;;;;;;;;;;;
Any suggestions will be greatly appreciated. Thanks
-Adam
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