Panic in Assembly Language

section .data
    error_msg db 'a problem', 0
    file_path db '/tmp/file', 0

section .text
    global _start

_start:
    ; Simulate a panic by calling a system exit with an error code
    mov eax, 1          ; syscall number for exit
    mov ebx, 1          ; exit status 1 to indicate error
    int 0x80            ; interrupt to invoke syscall

    ; The following code will not be executed due to the exit above
    ; but it demonstrates file creation and error handling

    ; Try to create a file
    mov eax, 8          ; syscall number for creat
    mov ebx, file_path  ; filename
    mov ecx, 0644o      ; file permissions
    int 0x80

    ; Check for error (negative value in eax)
    cmp eax, 0
    jl .file_error

    ; File created successfully, exit normally
    mov eax, 1          ; syscall number for exit
    xor ebx, ebx        ; exit status 0
    int 0x80

.file_error:
    ; Simulate a panic for file creation error
    mov eax, 1          ; syscall number for exit
    mov ebx, 1          ; exit status 1 to indicate error
    int 0x80

In Assembly Language, the concept of a panic doesn’t directly exist as it does in higher-level languages. Instead, we simulate a panic by immediately exiting the program with an error code. This achieves a similar effect of stopping execution when an unexpected condition occurs.

The code above first demonstrates an immediate “panic” by calling the exit system call with an error code. This is equivalent to the panic("a problem") in the original example.

After that, there’s code that attempts to create a file, which won’t be executed due to the previous exit. However, it’s included to show how you might handle errors in Assembly. If file creation fails (indicated by a negative value in the eax register), we jump to a label that exits the program with an error code, simulating a panic.

To run this program, you would typically need to assemble it into an object file and then link it:

$ nasm -f elf64 panic.asm
$ ld panic.o -o panic
$ ./panic

This would result in the program exiting with a non-zero status code, indicating an error occurred.

It’s important to note that in Assembly, error handling is much more manual and explicit compared to higher-level languages. There’s no built-in exception handling or panic mechanism, so developers must implement their own error checking and handling routines.

Unlike some high-level languages that use exceptions for handling many errors, in Assembly, it’s common to use return values or specific register states to indicate errors, and then explicitly check for these conditions in the code.