From 7d6af77804adc069a83e8566250f868a6cb9786e Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Tue, 29 Sep 2015 05:09:46 -0500
Subject: Make defconfig build for nommu.

Adds XVFORK() macro, teaches xpopen_both() to call /proc/self/exe with NULL
argv (and converts cpio -p to use that), adds TOYBOX_FORK guards to some
unconverted commands.
---
 lib/xwrap.c | 53 ++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 42 insertions(+), 11 deletions(-)

(limited to 'lib/xwrap.c')

diff --git a/lib/xwrap.c b/lib/xwrap.c
index e5dc4826..4880bbe0 100644
--- a/lib/xwrap.c
+++ b/lib/xwrap.c
@@ -129,6 +129,20 @@ void xflush(void)
   if (fflush(stdout) || ferror(stdout)) perror_exit("write");;
 }
 
+// This is called through the XVFORK macro because parent/child of vfork
+// share a stack, so child returning from a function would stomp the return
+// address parent would need. Solution: make vfork() an argument so processes
+// diverge before function gets called.
+pid_t xvforkwrap(pid_t pid)
+{
+  if (pid == -1) perror_exit("vfork");
+
+  // Signal to xexec() and friends that we vforked so can't recurse
+  toys.stacktop = 0;
+
+  return pid;
+}
+
 // Die unless we can exec argv[] (or run builtin command).  Note that anything
 // with a path isn't a builtin, so /bin/sh won't match the builtin sh.
 void xexec(char **argv)
@@ -144,25 +158,27 @@ void xexec(char **argv)
 }
 
 // Spawn child process, capturing stdin/stdout.
-// argv[]: command to exec. If null, child returns to original program.
-// pipes[2]: stdin, stdout of new process. If -1 will not have pipe allocated.
+// argv[]: command to exec. If null, child re-runs original program with
+//         toys.stacktop zeroed.
+// pipes[2]: stdin, stdout of new process, only allocated if zero on way in,
+//           pass NULL to skip pipe allocation entirely.
 // return: pid of child process
 pid_t xpopen_both(char **argv, int *pipes)
 {
   int cestnepasun[4], pid;
 
-  // Make the pipes? Not this won't set either pipe to 0 because if fds are
+  // Make the pipes? Note this won't set either pipe to 0 because if fds are
   // allocated in order and if fd0 was free it would go to cestnepasun[0]
   if (pipes) {
     for (pid = 0; pid < 2; pid++) {
-      if (pipes[pid] == -1) continue;
+      if (pipes[pid] != 0) continue;
       if (pipe(cestnepasun+(2*pid))) perror_exit("pipe");
       pipes[pid] = cestnepasun[pid+1];
     }
   }
 
-  // Child process
-  if (!(pid = xfork())) {
+  // Child process.
+  if (!(pid = CFG_TOYBOX_FORK ? xfork() : XVFORK())) {
     // Dance of the stdin/stdout redirection.
     if (pipes) {
       // if we had no stdin/out, pipe handles could overlap, so test for it
@@ -181,16 +197,31 @@ pid_t xpopen_both(char **argv, int *pipes)
         if (cestnepasun[3] > 2 || !cestnepasun[3]) close(cestnepasun[3]);
       }
     }
-    if (argv) {
-      if (CFG_TOYBOX) toy_exec(argv);
-      execvp(argv[0], argv);
+    if (argv) xexec(argv);
+
+    // In fork() case, force recursion because we know it's us.
+    if (CFG_TOYBOX_FORK) {
+      toy_init(toys.which, toys.argv);
+      toys.stacktop = 0;
+      toys.which->toy_main();
+      xexit();
+    // In vfork() case, exec /proc/self/exe with high bit of first letter set
+    // to tell main() we reentered.
+    } else {
+      char *s = "/proc/self/exe";
+
+      // We did a nommu-friendly vfork but must exec to continue.
+      // setting high bit of argv[0][0] to let new process know
+      **toys.argv |= 0x80;
+      execv(s, toys.argv);
+      perror_msg(s);
+
       _exit(127);
     }
-    return 0;
-
   }
 
   // Parent process
+  if (!CFG_TOYBOX_FORK) **toys.argv &= 0x7f;
   if (pipes) {
     if (pipes[0] != -1) close(cestnepasun[0]);
     if (pipes[1] != -1) close(cestnepasun[3]);
-- 
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