feat(app): nolibc hello world

app/entry.s

@@ -0,0 +1,29 @@
+.global _start, syscall5
+
+
+_start: 
+    /* Load argc -> rdi, argv[0] -> rsi */
+    xor %rbp, %rbp
+    pop %rdi
+    mov %rsp, %rsi
+
+    and $0xFFFFFFFFFFFFFFF0, %rsp
+    
+    call main
+
+    /* Exit with ret val of main */
+    mov %rax, %rdi
+    mov $0x3C, %rax
+    syscall
+
+syscall5:
+    mov    %rdi, %rax /* %rax (syscall number)  = func param 1 (%rdi)    */
+    mov    %rsi, %rdi /* %rdi (syscall param 1) = func param 2 (%rsi)    */
+    mov    %rdx, %rsi /* %rsi (syscall param 2) = func param 3 (%rdx)    */
+    mov    %rcx, %rdx /* %rdx (syscall param 3) = func param 4 (%rcx)    */
+    mov    %r8,  %r10 /* %r10 (syscall param 4) = func param 5 (%r8)     */
+    mov    %r9,  %r8  /* %r8  (syscall param 5) = func param 6 (%r9)     */
+    syscall           /* Enter a syscall (return value in %rax)          */
+    ret               /* Return value is already in %rax, we can return. */
+    
+.section .note.GNU-stack,"",@progbits