Try to use x4 instead of x2

Also adds os as x3. May get aarch64 FreeBSD working.

cosmo now traps on unsupported os, and cosmo and Launch both take os and
exename at the same registers.

__program_executable_name is a decentralized init on x64, so shouldn't
be paid for if not used.

ape/ape-m1.c

@@ -725,12 +725,12 @@ __attribute__((__noreturn__)) static void Spawn(const char *exe, int fd,
   close(fd);
 
   register long *x0 __asm__("x0") = sp;
-  register char *x2 __asm__("x2") = path;
+  register int   x3 __asm__("x3") = 8 /* XNU */;
+  register char *x4 __asm__("x4") = path;
   register struct Syslib *x15 __asm__("x15") = lib;
   register long x16 __asm__("x16") = e->e_entry;
   __asm__ volatile("mov\tx1,#0\n\t"
-                   "mov\tx3,#0\n\t"
-                   "mov\tx4,#0\n\t"
+                   "mov\tx2,#0\n\n"
                    "mov\tx5,#0\n\t"
                    "mov\tx6,#0\n\t"
                    "mov\tx7,#0\n\t"
@@ -758,7 +758,7 @@ __attribute__((__noreturn__)) static void Spawn(const char *exe, int fd,
                    "mov\tx0,#0\n\t"
                    "br\tx16"
                    : /* no outputs */
-                   : "r"(x0), "r"(x2), "r"(x15), "r"(x16)
+                   : "r"(x0), "r"(x3), "r"(x4), "r"(x15), "r"(x16)
                    : "memory");
   __builtin_unreachable();
 }

ape/launch.S

@@ -31,17 +31,17 @@
 //
 //	@param	rdi is passed through as-is
 //	@param	rsi is address of entrypoint (becomes zero)
-//	@param	rdx is passed through as-is
-//	@param	rcx is stack pointer (becomes r8)
+//	@param	rdx is stack pointer (becomes zero)
+//	@param	rcx is passed through as-is
+//	@param	r8  is passed through as-is
 //	@noreturn
 Launch:
 #ifdef __aarch64__
 
 	mov	x16,x1
-	mov	sp,x3
+	mov	sp,x2
 	mov	x1,0
-	mov	x3,x4
-	mov	x4,0
+	mov	x2,0
 	mov	x5,0
 	mov	x6,0
 	mov	x7,0
@@ -70,9 +70,6 @@ Launch:
 
 #else
 
-	mov	%rcx,%rsp
-	mov	%r8,%rcx
-	xor	%r8d,%r8d
 	xor	%r9d,%r9d
 	xor	%r10d,%r10d
 	xor	%r11d,%r11d
@@ -80,6 +77,8 @@ Launch:
 	xor	%r13d,%r13d
 	xor	%r14d,%r14d
 	xor	%r15d,%r15d
+	mov	%rdx,%rsp
+	xor	%edx,%edx
 	push	%rsi
 	xor	%esi,%esi
 	xor	%ebp,%ebp

ape/loader.c

@@ -225,7 +225,7 @@ struct ApeLoader {
 
 EXTERN_C long SystemCall(long, long, long, long, long, long, long, int);
 EXTERN_C void
-Launch(void *, long, void *, void *, int) __attribute__((__noreturn__));
+Launch(void *, long, void *, int, void *) __attribute__((__noreturn__));
 
 extern char __executable_start[];
 extern char _end[];
@@ -768,7 +768,7 @@ __attribute__((__noreturn__)) static void Spawn(int os, char *exe, int fd,
   Msyscall(dynbase + code, codesize, os);
 
   /* call program entrypoint */
-  Launch(IsFreebsd() ? sp : 0, dynbase + e->e_entry, exe, sp, os);
+  Launch(IsFreebsd() ? sp : 0, dynbase + e->e_entry, sp, os, exe);
 }
 
 static const char *TryElf(struct ApeLoader *M, union ElfEhdrBuf *ebuf,

libc/crt/crt.S

@@ -62,8 +62,6 @@ _start:
 //	set operating system when already detected
 1:	mov	%cl,__hostos(%rip)
 
-	mov	%rdx,__program_executable_name(%rip)
-
 //	get startup timestamp as early as possible
 //	its used by --strace flag and kprintf() %T
 	rdtsc
@@ -142,7 +140,9 @@ _start:
 //	should be set to zero on other platforms
 	mov	x1,x15
 
-//	third arg (x2) is the program path passed by ape-m1.c
+//	3rd arg (x2) is unused (stack pointer on x86_64)
+//	4th arg (x3) is os passed by loader
+//	5th arg (x4) is program executable name passed by loader
 
 //	switch to c code
 	bl	cosmo

libc/nexgen32e/program_executable_name.S

@@ -0,0 +1,32 @@
+/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
+│ vi: set noet ft=asm ts=8 sw=8 fenc=utf-8                                 :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/macros.internal.h"
+#include "libc/notice.inc"
+
+	.initbss 300,_init_program_executable_name
+//	Global variable holding the binary that we are running as
+__program_executable_name:
+	.quad	0
+	.endobj	__program_executable_name,globl
+	.previous
+
+	.init.start 300,_init_program_executable_name
+	mov	%r8,%rax
+	stosq
+	.init.end 300,_init_program_executable_name

libc/nexgen32e/program_executable_name2.c

@@ -17,5 +17,8 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/runtime/runtime.h"
+#ifndef __x86_64__
 
 char *__program_executable_name;
+
+#endif /* __x86_64__ */

libc/runtime/cosmo2.c

@@ -78,7 +78,8 @@ static const char *DecodeMagnum(const char *p, long *r) {
   return *r = x, p;
 }
 
-wontreturn textstartup void cosmo(long *sp, struct Syslib *m1, char *exename) {
+wontreturn textstartup void cosmo(long *sp, struct Syslib *m1, int, int os,
+                                  char *exename) {
 
   // get startup timestamp as early as possible
   // its used by --strace and also kprintf() %T
@@ -112,17 +113,24 @@ wontreturn textstartup void cosmo(long *sp, struct Syslib *m1, char *exename) {
   program_invocation_name = argv[0];
   __oldstack = (intptr_t)sp;
 
-  // detect apple m1 environment
   const char *magnums;
-  if (SupportsXnu() && (__syslib = m1)) {
-    hostos = _HOSTXNU;
+  switch (os) {
+    case _HOSTXNU: {
+      npassert(SupportsXnu() && m1);
+      __syslib = m1;
       magnums = syscon_xnu;
-  } else if (SupportsLinux()) {
-    hostos = _HOSTLINUX;
-    magnums = syscon_linux;
-  } else {
-    notpossible;
+      break;
     }
+    case _HOSTLINUX: {
+      npassert(SupportsLinux());
+      magnums = syscon_linux;
+      break;
+    }
+    default: {
+      npassert(!"supported-os");
+    }
+  }
+  hostos = os;
 
   // setup system magic numbers
   for (long *mp = syscon_start; mp < syscon_end; ++mp) {