Tjyylli

Can you let me know what I'm doing wrong?

I'm new to assembly programming and am unfamiliar with the various options in ld.

I've been trying to use the yasm compiler initially but then realised that as is the way to go for the ARM architecture while composing GNU compliant assembly code.

Better luck running as from the binutils package I. E.,the GNU assembler. But the assembly code has to be Arm-compliant.

The following is the code within arm.s:

 .global main                      /* declares the main identifier */ 

 .type main , % function main :    /* Address of the main function */ 

  /* Program code would go here */ 

  BR LR 

  /* Return to the caller */

 .end                              /* End of the program */

ARM, a RISC architecture, is not supported by YASM.

My build file is as follows:

#/usr/bin/env bash
#display usage
[ $# -eq 0 ] && { echo "Usage: $0 ";exit 1; }
set +e
rm -f $1.exe $1 $1.o
as -o $1.o $1.s
[ -e $1.o ] && { file $1.o;}
gcc -s -o $1.exe $1.o -fpic
ld -s -o $1 -pie --dynamic-linker /system/bin/linker64 /data/data/com.termux/files/usr/lib/crtbegin_dynamic.o $1.o -lc -lgcc -ldl /data/data/com.termux/files/usr/lib/crtend_android.o
[ -e $1.exe ] && { file $1.exe;nohup ./$1.exe; }

[ -e $1 ] && { file $1;nohup ./$1;}
set -e

The code was causing either a segmentation fault or a bus error earlier.

I was able to run a program or two without any segmentation or bus errors with the updated build file above. I set up the build file to produce two executables, one using gcc and the other ld, since some online tutorials use ld instead of gcc for the linking step. Using the verbose setting of gcc, you can look at the options passed to the linker and thus mimic the same for the linker independently.

There may be some redundant settings that I've missed.

You can access updates to the source code and build file at
Learn Assembly.

Check out this resource from Keil here. arm Keil product guides

More resources:

https://thinkingeek.com/2016/10/08/exploring-aarch64-assembler-chapter1/

https://stackoverflow.com/q/3577922/3924108

While the above problem appears to be fixed for now, I have errors running the following code:

.text .global main main: mov w0, #2 mov w7, #1 // request to exit program svc 0


I obtain an illegal instruction error when I try to execute the code.

Secondly, if I alter the main to _start (since I don't want to be using main all the time), I have the following error from the buildrun script.

./buildrun myprogram

/data/data/com.termux/files/usr/bin/aarch64-linux-android-ld: myprogram.o: in function _start': (.text+0x0): multiple definition of_start'; /data/data/com.termux/files/usr/lib/crtbegin_dynamic.o:crtbegin.c:(.text+0x0): first defined here /data/data/com.termux/files/usr/bin/aarch64-linux-android-ld: /data/data/com.termux/files/usr/lib/crtbegin_dynamic.o: in function _start_main': crtbegin.c:(.text+0x38): undefined reference tomain
/data/data/com.termux/files/usr/bin/aarch64-linux-android-ld: crtbegin.c:(.text+0x3c): undefined reference to main' clang-8: error: linker command failed with exit co
de 1 (use -v to see invocation)
ld: myprogram.o: in function_start': (.text+0x0): multiple definition of _start'; /data/data/com.termux/files/usr/lib/crtbegin_dynamic.o:crtbegin.c:(.text+0x0): first defined here ld: /data/data/com.termux/files/usr/lib/crtbegin_dynamic.o: in function_start_main': crtbegin.c:(.text+0x38): undefined reference to main'
ld: crtbegin.c:(.text+0x3c): undefined reference tomain'

How do I create programs with entry points other than main?

I want to be able to :

Create a statically linked executable that works.
Create an executable that has a function named _start instead of main.
Create a dynamically linked executable with an entry point other than main.
Create an executable that uses supervisor call svc to exit without throwing an illegal instruction error as against using ret.

Reference:

https://thinkingeek.com/2013/01/09/arm-assembler-raspberry-pi-chapter-1/

Check the comment by ehrt74 on the above post.

Yasm is an x86 assembler. It cannot produce executables for an ARM processor.

The tutorials you are working with are describing x86 assembly. They are intended to be followed on an x86 system.