1 files changed, 27 insertions, 0 deletions
diff --git a/02_process_init/entry.S b/02_process_init/entry.S
new file mode 100644
index 0000000..50425ba
--- /dev/null
+++ b/02_process_init/entry.S
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Johannes Stoelp
+
+#include <asm/unistd.h>
+
+.intel_syntax noprefix
+
+.section .text, "ax", @progbits
+.global _start
+_start:
+    // $rsp is guaranteed to be 16-byte aligned.
+
+    // Clear $rbp as specified by the SysV AMD64 ABI.
+    xor rbp, rbp
+
+    // Load pointer to process context prepared by execve(2) syscall as
+    // specified in the SysV AMD64 ABI.
+    // Save pointer in $rdi which is the arg0 (int/ptr) register.
+    lea rdi, [rsp]
+
+    // Stack frames must be 16-byte aligned before control is transfered to the
+    // callees entry point.
+    call entry
+
+    // Call exit(0) syscall.
+    mov rdi, 0
+    mov rax, __NR_exit
+    syscall