Okay so i tried to open two file , first file called test.asm that i created using
echo mov ax,5 > test.asm
Then i have another file called sambungstring.asm that i created manually
I tried to compile the file using this command
nasm <filename>.asm -o <filename>.com
I can compile test.asm but why does sambungstring.asm gives error ?!?! they're located at exact same location
As can be seen in the image , test.asm compiled successfully and test.com appeared in the directory , but sambungstring.asm gives error.
Please help me , i've already spent 3 days trying to install nasm and running it in dosbox , this is the first time i finally able to run nasm in dosbox .
Related
I'm getting a weird error message when trying to assemble and run a .s file using AT&T Intel Syntax. Not sure if I'm even using the correct architecture to begin with, or if I'm having syntax errors, if I'm not using the correct commands to assemble and link, etc. Completely lost and I do not know where to begin.
So basically, I have a file called yea.s , which contains some simple assembler instructions. I then try to compile it using the command as yea.s -o yea.o and then link is using ld yea.o -o yea. When running ld, I get this weird message:ld: warning: cannot find entry symbol _start; defaulting to 000000440000.
This is the program im trying to run, very simple and doesn't really do anything.
resMsg: .asciz "xxxxxxxx"
.text
.global main
main:
pushq $0
ret
I just cannot figure out what's going on. Obviously, this is for school homework. I'm not looking for the answer to the homework, obviously, but this is the starting point to where I can actually start the coding. And I just cant figure out how to simple run the program, which it doesn't say in the assignment. Anyway, thanks in advance guys!
Linux executables require an entry point to be specified. The entry point is the address of the first instruction to be executed in your program. If not specified otherwise, the link editor looks for a symbol named _start to use as an entry point. Your program does not contain such a symbol, thus the linker complains and picks the beginning of the .text section as the entry point. To fix this problem, rename main to _start.
Note further that unlike on DOS, there is nothing to return to from _start. So your attempt to return is going to cause a crash. Instead, call the system call sys_exit to exit the program:
mov $0, %edi # exit status
mov $60, %eax # system call number
syscall # perform exit call
Alternatively, if you want to use the C runtime environment and call functions from the C library, leave your program as is and instead assemble and link using the C compiler driver cc:
cc -o yea yea.s
If you do so, the C runtime environment provides the entry point for you and eventually tries to call a function main which is where your code comes in. This approach is required if you want to call functions from the C library. If you do it this way, make sure that main follows the SysV ABI (calling convention).
Note that even then your code is incorrect. The return value of a function is given in the eax (resp. rax) register and not pushed on the stack. To return zero from main, write
mov $0, %eax # exit status
ret # return from function
In all currently supported versions of Ubuntu open the terminal and type:
sudo apt install as31 nasm
as31: Intel 8031/8051 assembler
This is a fast, simple, easy to use Intel 8031/8051 assembler.
nasm: General-purpose x86 assembler
Netwide Assembler. NASM will currently output flat-form binary files, a.out, COFF and ELF Unix object files, and Microsoft 16-bit DOS and Win32 object files.
If you are using NASM in Ubuntu 18.04, the commands to compile and run an .asm file named example.asm are:
nasm -f elf64 example.asm # assemble the program
ld -s -o example example.o # link the object file nasm produced into an executable file
./example # example is an executable file
I am new to linux programming and learning it from The Linux Programming Interface by Michael Kerrisk.
I have to compile my first program that has dependencies.
Directory structure:
--linux-programs
|--seek_io.c
|--lib
|--tlpi_hdr.h
|--error_functions.h
|--error_functions.c
|--get_num.h
|--ename.c.inc
I want to compile seek_io.c program with dependencies in the lib directory, so that I can see how the program works.
I tried a few things, absolutely clueless on how they work following this stackoverflow answer. I get all sorts of errors as I am an absolute beginner to Linux programming, not to programming, linux OS and C.
Trials:
gcc -I ./lib/ -c ./lib/error_functions.c and then gcc -o seek_io.c ./error_function.o gives error:
/usr/lib/gcc/x86_64-linux-gnu/crt1.o: In function _start:
(.text+0x20): undefined reference to main
collect2: error: ld returned 1 exit status
After this run, on ls I find that my seek_io.c is not listed.
Basically the author of the book says for tlpi_hdr.h file:
This header file includes various other header files used by many of the example programs, defines a Boolean data type, and defines macros for calculating the minimum and maximum of two numeric values. Using this header file allows us to make the example programs a bit shorter.
Link to codes for files mentioned above:
tlpi_hdr.h
error_functions.h
error_functions.c
get_num.h
get_num.c
seek_io.c
The problem is with your second gcc command, where you're using the -o file to specify the output file where to store the resulting executable file, but passing it the name of the C source file seek_io.c instead...
gcc -o seek_io.c ./error_function.o
This means link file error_function.o and store the executable in seek_io.c. This fails because there is no main function, which is needed for a standalone executable, so your C source file is not overwritten by the failing link command.
You can fix this easily by passing the -o option a proper output file name, which in the case (of this link command) should be the name of the executable that you want to create, such as seek_io:
gcc -o seek_io seek_io.c ./error_function.o
(But this will fail without a -I ./lib/, since seek_io.c includes tlpi_hdr.h which is in that directory. If you add it to that command, it should work.)
You can also decide to split the compile and link steps in two separate steps (the command above will both compile seek_io.c into an object file and then link the two object files into an executable) with:
$ gcc -I ./lib/ -c ./lib/error_functions.c
$ gcc -I ./lib/ -c seek_io.c
$ gcc -o seek_io seek_io.o error_function.o
One final nitpick is that for the -I flag to specify the directories where to search for the include files, the more common usage has no space between the flag itself and the directory name, so you'll most commonly see -I./lib or even -Ilib.
$ gcc -Ilib -c ./lib/error_functions.c
$ gcc -Ilib -c seek_io.c
$ gcc -o seek_io seek_io.o error_function.o
I am trying to follow the exercise in the book PC Assembly by Paul Carter. http://pacman128.github.io/pcasm/
I'm trying to run the program from 1.4 page 23 on Ubuntu 18. The files are all available on the github site above.
Since original code is for 32bit I compile using
nasm -f elf32
for first.asm and asm_io.asm to get the object files. I also compile driver.c
I use the linker from gcc and run
gcc -m32 -o first first.o asm_io.o driver.o
but it keeps giving me a bun of errors like
undefined reference to '_scanf'
undefined reference to '_printf'
(note _printf appears instead of printf because some conversion is done in the file asm_io.asm to maintain compatibility between windows and linux OS's)
I don't know why these errors are appearing. I also try running using linker directly
ld -m elf_i386 -e main -o first -first.o driver.o asm_io.o -I /lib/i386-linux-gnu/ld-linux.so.2
and many variations since it seems that its not linking with the C libraries.
Any help? Stuck on this for a while and couldn't find a solution on similar questions
Linux doesn't prepend _ to names when mapping from C to asm symbol names in ELF object files1.
So call printf, not _printf, because there is no _printf in libc.
Whatever "compatibility" code did that is doing it wrong. Only Windows and OS X use _printf, Linux uses printf.
So either you've misconfigured something or defined the wrong setting, or it requires updating / porting to Linux.
Footnote 1: In ancient history (like over 20 years ago), Linux with the a.out file format did use leading underscores on symbol names.
Update: the library uses the NASM preprocessor to %define _scanf scanf and so on, but it requires you to manually define ELF_TYPE by assembling with nasm -d ELF_TYPE.
They could have detected ELF32 or ELF64 output formats on their own, because NASM pre-defines __OUTPUT_FORMAT__. Someone should submit a pull-request to make this detection automatic with code something like this:
%ifidn __OUTPUT_FORMAT__, elf32
%define ELF_TYPE 32
%elifidn __OUTPUT_FORMAT__, elf64
%define ELF_TYPE 64
%endif
%ifdef ELF_TYPE
...
%endif
I'm learning NASM and DEBUG using Windows XP (32-bit) for academic purposes. I'm struggling to get my first simple HelloWorld program to work. It's called prog1.asm.
Here is the code for my prog1.asm file:
bits 16
org 0x100 ; Start program at offset 100h
jmp main ; Jump to main program
message: db 'Hello world',0ah, 0dh,'$'
main: mov dx,message ; Start address of message
mov ah,09 ; Prepare for screen display
int 21h ; DOS interrupt 21h
int 20h ; Terminate program
This code above is just written out from the book that I've been using to study, as you're probably aware I'm like brand new to this. I have nasm.exe in the directory that I'm working with here.
When I'm in my directory, I run nasm -f prog1.asm -o progm1.com -l prog1.lst in an attempt to use the prog1.asm file to create the executable file prog1.com that is created by NASM and an output listing file prog1.lst also produced by NASM.
Running this command gives me the following error:
nasm: fatal: unrecognized output format 'prog1.asm' - use -hf for a list
type 'nasm -h'for help
If anyone is familiar with this problem and can help, it'd be much appreciated, let me know if more details are required.
-f option selects output format. Try this:
nasm prog1.asm -f bin -o progm1.com -l prog1.lst
I compile this program:
#include <stdio.h>
int main()
{
printf("Hello World!");
return 0;
}
With this command:
gcc -c "hello.c" -o hello
And when I try to execute hello, I get
bash: ./hello: Permission denied
Because the permissions are
-rw-r--r-- 1 nathan nathan 856 2010-09-17 23:49 hello
For some reason??
But whatever... after changing the permissions and trying to execute again, I get
bash: ./hello: cannot execute binary file
I'm using gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3
What am I doing wrong here? It's gotta be obvious... it's just too late for me to keep using my tired eyes to try and figure out this simple problem....
P.S. I do (sometimes) work on programs more sophisticated than Hello World, but gcc is doing this across the board...
Take the -c out. That's for making object files, not executables.
The -c flag tells it not to link, so you have an object file, not a binary executable.
In fact, if you ran this without the -o flag, you would find that the default output file would be hello.o.
For reference (and giggles), the man entry on the -c flag:
-c Compile or assemble the source files, but do not link. The linking stage simply is not done.
The ultimate output is in the form of an object file for each source file.
By default, the object file name for a source file is made by replacing the suffix .c, .i, .s,
etc., with .o.
Unrecognized input files, not requiring compilation or assembly, are ignored.
Compile with: gcc hello.c -o hello