CODEWITHSUNDEEP
linux
user1752418
user1752418

Reputation: 21

Segmentation fault in linux 64 bit assembly language (Beginner)

Getting a segmentation fault and output is not as desired in linux 64 bit assembly language. Beginner. Any help would be appreciated. Seeking help first here before I speak to TA/professor. Here is the link to the site for reference: http://www.cs.fsu.edu/~langley/CIS4385-2014-1/Assign2-new.html

Here is my code thus far:

.text                           # Start of code segment

.global _start              # Declaring for linker (ld)

_start:
                            # String to stdout

      movl    $len,%edx           # Argument: message length
      movl    $msg,%ecx           # Argument: pointer to message to write
      movl    $1,%ebx             # Argument: file handle (stdout)
      movl    $4,%eax             # System call number (sys_write)
      syscall                     # Invokes system calls in Linux

      movl    $0,%ebx             # Argument: exit code
      movl    $1,%eax             # System call number (sys_exit)
      syscall                     # Invokes system calls in Linux

.data                           # Start of data segment

msg:
    .ascii    "Hello World (64 bit version) --- this is MY NAME!\n"
    .ascii    "\n"
    .ascii    "CIS 4385 Spring 2014\n"
    len = . - msg                 # length of string

Upvotes: 0

Views: 142

Answers (1)

nodakai
nodakai

Reputation: 8033

You confused x86 assembly with x86_64 assembly.

  1. Register names are different. %edx vs %rdx, %ebx vs %rdi, ... You need to read about x86_64 conventions. It isn't a simple replacement from %e.. to %r.. !
    Plus, if you just write mov $1,%rax, then GNU as(1) will choose an appropriate variant of mov for you (movq in this case)
  2. Syscall numbers are different. SYS_write is 1, for example. See /usr/include/asm/unistd_64.h for the full list.

FYI, this is how to use GDB:

$ gdb -tui ./your.exe -ex 'break _start' -ex run
(gdb) layout next
(gdb) (hit Enter, Enter... until you get a desired view)
(gdb) nexti # or stepi, if you want to go into a function call
(gdb) (hit Enter, Enter, ...)

Upvotes: 3

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