86

Author: ktye

x/l86.h

@@ -0,0 +1,39 @@
+// -nostdlib -ffreestanding
+
+//gcc -nostdlib -static
+
+asm(
+        ".global _start\n"
+        "_start:\n"
+        "   xorl %ebp,%ebp\n"       // mark outermost stack frame
+        "   movq 0(%rsp),%rdi\n"    // get argc
+        "   lea 8(%rsp),%rsi\n"     // the arguments are pushed just below, so argv = %rbp + 8
+        "   call bare_main\n"       // call our bare_main
+        "   movq %rax,%rdi\n"       // take the main return code and use it as first argument for...
+        "   movl $60,%eax\n"        // ... the exit syscall
+        "   syscall\n"
+        "   int3\n");               // just in case
+
+asm(
+        "bare_write:\n"             // write syscall wrapper; the calling convention is pretty much ok as is
+        "   movq $1,%rax\n"         // 1 = write syscall on x86_64
+        "   syscall\n"
+        "   ret\n");
+
+
+int bare_write(int fd, const void *buf, unsigned count);
+
+unsigned my_strlen(const char *ch) {
+    const char *ptr;
+    for(ptr = ch; *ptr; ++ptr);
+    return ptr-ch;
+}
+
+int bare_main(int argc, char *argv[]) {
+    for(int i = 0; i < argc; ++i) {
+        int len = my_strlen(argv[i]);
+        bare_write(1, argv[i], len);
+        bare_write(1, "\n", 1);
+    }
+    return argc;
+}