diff mbox series

[libiberty] PEX-unix forking

Message ID 593c010d-0d12-cbf9-e1a9-e0f3108ffdf8@acm.org
State New
Headers show
Series [libiberty] PEX-unix forking | expand

Commit Message

Nathan Sidwell Aug. 20, 2018, 5:38 p.m. UTC 
This is the first of a pair of patches I've had on the modules branch 
for a while.  They improve the error behaviour in the case of child 
failure when vfork is the forking mechanism.

This one commonizes the error paths in the parent and child to a pair of 
single blocks that print or return the error respectively.  Currently 
each error case calls pex_child_error, or returns the error in the parent.

The patch records the name of a failing system call, and uses that to 
print or return the error.  It doesn't change functionality but will 
simplify the next patch that does.

booted on x86_64-linux (which uses vfork), ok?

nathan

Comments

Li, Pan2 via Gcc-patches Aug. 20, 2018, 9:36 p.m. UTC | #1 
On Mon, Aug 20, 2018 at 10:38 AM, Nathan Sidwell <nathan@acm.org> wrote:
>
> This is the first of a pair of patches I've had on the modules branch for a
> while.  They improve the error behaviour in the case of child failure when
> vfork is the forking mechanism.
>
> This one commonizes the error paths in the parent and child to a pair of
> single blocks that print or return the error respectively.  Currently each
> error case calls pex_child_error, or returns the error in the parent.
>
> The patch records the name of a failing system call, and uses that to print
> or return the error.  It doesn't change functionality but will simplify the
> next patch that does.
>
> booted on x86_64-linux (which uses vfork), ok?


+      if (!bad_fn && in != STDIN_FILE_NO && close (in) < 0)
+        bad_fn = "close";

As a matter of style I don't personally like the pattern in which a
condition has both tests and actions.  It's too easy to miss the
action.  I would prefer to see this more like the original code:

    if (!bad_fn && in != STDIN_FILE_NO)
      {
        if (close(in) < 0)
            bad_fn = "close";
      }

This is OK with those changes.

Thanks.

Ian
Nathan Sidwell Aug. 21, 2018, midnight UTC | #2 
On 08/20/2018 05:36 PM, Ian Lance Taylor wrote:

> As a matter of style I don't personally like the pattern in which a
> condition has both tests and actions.  It's too easy to miss the
> action.  I would prefer to see this more like the original code:
> 
>      if (!bad_fn && in != STDIN_FILE_NO)
>        {
>          if (close(in) < 0)
>              bad_fn = "close";
>        }
> 
> This is OK with those changes.

Fair enough, committing the attached.  I've elided the unnecessary braces, as 
there are no trailing elses in this case.

nathan
diff mbox series

Patch

2018-08-20  Nathan Sidwell  <nathan@acm.org>

	* pex-unix.c (pex_child_error): Delete.
	(pex_unix_exec_child): Commonize error paths to single message &
	exit.

Index: pex-unix.c
===================================================================
--- pex-unix.c	(revision 263667)
+++ pex-unix.c	(working copy)
@@ -298,8 +298,6 @@  pex_wait (struct pex_obj *obj, pid_t pid
 #endif /* ! defined (HAVE_WAITPID) */
 #endif /* ! defined (HAVE_WAIT4) */
 
-static void pex_child_error (struct pex_obj *, const char *, const char *, int)
-     ATTRIBUTE_NORETURN;
 static int pex_unix_open_read (struct pex_obj *, const char *, int);
 static int pex_unix_open_write (struct pex_obj *, const char *, int, int);
 static pid_t pex_unix_exec_child (struct pex_obj *, int, const char *,
@@ -366,28 +364,6 @@  pex_unix_close (struct pex_obj *obj ATTR
   return close (fd);
 }
 
-/* Report an error from a child process.  We don't use stdio routines,
-   because we might be here due to a vfork call.  */
-
-static void
-pex_child_error (struct pex_obj *obj, const char *executable,
-		 const char *errmsg, int err)
-{
-  int retval = 0;
-#define writeerr(s) retval |= (write (STDERR_FILE_NO, s, strlen (s)) < 0)
-  writeerr (obj->pname);
-  writeerr (": error trying to exec '");
-  writeerr (executable);
-  writeerr ("': ");
-  writeerr (errmsg);
-  writeerr (": ");
-  writeerr (xstrerror (err));
-  writeerr ("\n");
-#undef writeerr
-  /* Exit with -2 if the error output failed, too.  */
-  _exit (retval == 0 ? -1 : -2);
-}
-
 /* Execute a child.  */
 
 #if defined(HAVE_SPAWNVE) && defined(HAVE_SPAWNVPE)
@@ -592,21 +568,22 @@  pex_unix_exec_child (struct pex_obj *obj
                      int in, int out, int errdes,
 		     int toclose, const char **errmsg, int *err)
 {
-  pid_t pid;
+  pid_t pid = -1;
 
   /* We declare these to be volatile to avoid warnings from gcc about
      them being clobbered by vfork.  */
-  volatile int sleep_interval;
+  volatile int sleep_interval = 1;
   volatile int retries;
 
   /* We vfork and then set environ in the child before calling execvp.
      This clobbers the parent's environ so we need to restore it.
      It would be nice to use one of the exec* functions that takes an
-     environment as a parameter, but that may have portability issues.  */
+     environment as a parameter, but that may have portability
+     issues.   */
   char **save_environ = environ;
 
-  sleep_interval = 1;
-  pid = -1;
+  const char *bad_fn = NULL;
+
   for (retries = 0; retries < 4; ++retries)
     {
       pid = vfork ();
@@ -625,57 +602,76 @@  pex_unix_exec_child (struct pex_obj *obj
 
     case 0:
       /* Child process.  */
-      if (in != STDIN_FILE_NO)
+      if (!bad_fn && in != STDIN_FILE_NO)
 	{
 	  if (dup2 (in, STDIN_FILE_NO) < 0)
-	    pex_child_error (obj, executable, "dup2", errno);
-	  if (close (in) < 0)
-	    pex_child_error (obj, executable, "close", errno);
+	    bad_fn = "dup2";
+	  else if (close (in) < 0)
+	    bad_fn = "close";
 	}
-      if (out != STDOUT_FILE_NO)
+      if (!bad_fn && out != STDOUT_FILE_NO)
 	{
 	  if (dup2 (out, STDOUT_FILE_NO) < 0)
-	    pex_child_error (obj, executable, "dup2", errno);
-	  if (close (out) < 0)
-	    pex_child_error (obj, executable, "close", errno);
+	    bad_fn = "dup2";
+	  else if (close (out) < 0)
+	    bad_fn = "close";
 	}
-      if (errdes != STDERR_FILE_NO)
+      if (!bad_fn && errdes != STDERR_FILE_NO)
 	{
 	  if (dup2 (errdes, STDERR_FILE_NO) < 0)
-	    pex_child_error (obj, executable, "dup2", errno);
-	  if (close (errdes) < 0)
-	    pex_child_error (obj, executable, "close", errno);
+	    bad_fn = "dup2";
+	  else if (close (errdes) < 0)
+	    bad_fn = "close";
 	}
-      if (toclose >= 0)
+      if (!bad_fn && toclose >= 0)
 	{
 	  if (close (toclose) < 0)
-	    pex_child_error (obj, executable, "close", errno);
+	    bad_fn = "close";
 	}
-      if ((flags & PEX_STDERR_TO_STDOUT) != 0)
+      if (!bad_fn && (flags & PEX_STDERR_TO_STDOUT) != 0)
 	{
 	  if (dup2 (STDOUT_FILE_NO, STDERR_FILE_NO) < 0)
-	    pex_child_error (obj, executable, "dup2", errno);
+	    bad_fn = "dup2";
 	}
-
-      if (env)
+      if (!bad_fn)
 	{
-	  /* NOTE: In a standard vfork implementation this clobbers the
-	     parent's copy of environ "too" (in reality there's only one copy).
-	     This is ok as we restore it below.  */
-	  environ = (char**) env;
+	  if (env)
+	    /* NOTE: In a standard vfork implementation this clobbers
+	       the parent's copy of environ "too" (in reality there's
+	       only one copy).  This is ok as we restore it below.  */
+	    environ = (char**) env;
+	  if ((flags & PEX_SEARCH) != 0)
+	    {
+	      execvp (executable, to_ptr32 (argv));
+	      bad_fn = "execvp";
+	    }
+	  else
+	    {
+	      execv (executable, to_ptr32 (argv));
+	      bad_fn = "execv";
+	    }
 	}
 
-      if ((flags & PEX_SEARCH) != 0)
-	{
-	  execvp (executable, to_ptr32 (argv));
-	  pex_child_error (obj, executable, "execvp", errno);
-	}
-      else
-	{
-	  execv (executable, to_ptr32 (argv));
-	  pex_child_error (obj, executable, "execv", errno);
-	}
+      /* Something failed, report an error.  We don't use stdio
+	 routines, because we might be here due to a vfork call.  */
+      {
+	ssize_t retval = 0;
+	int err = errno;
+
+#define writeerr(s) (retval |= write (STDERR_FILE_NO, s, strlen (s)))
+	writeerr (obj->pname);
+	writeerr (": error trying to exec '");
+	writeerr (executable);
+	writeerr ("': ");
+	writeerr (bad_fn);
+	writeerr (": ");
+	writeerr (xstrerror (err));
+	writeerr ("\n");
+#undef writeerr
 
+	/* Exit with -2 if the error output failed, too.  */
+	_exit (retval < 0 ? -2 : -1);
+      }
       /* NOTREACHED */
       return (pid_t) -1;
 
@@ -689,32 +685,18 @@  pex_unix_exec_child (struct pex_obj *obj
 	 the child's copy of environ.  */
       environ = save_environ;
 
-      if (in != STDIN_FILE_NO)
-	{
-	  if (close (in) < 0)
-	    {
-	      *err = errno;
-	      *errmsg = "close";
-	      return (pid_t) -1;
-	    }
-	}
-      if (out != STDOUT_FILE_NO)
-	{
-	  if (close (out) < 0)
-	    {
-	      *err = errno;
-	      *errmsg = "close";
-	      return (pid_t) -1;
-	    }
-	}
-      if (errdes != STDERR_FILE_NO)
-	{
-	  if (close (errdes) < 0)
-	    {
-	      *err = errno;
-	      *errmsg = "close";
-	      return (pid_t) -1;
-	    }
+      if (!bad_fn && in != STDIN_FILE_NO && close (in) < 0)
+	bad_fn = "close";
+      if (!bad_fn && out != STDOUT_FILE_NO && close (out) < 0)
+	bad_fn = "close";
+      if (!bad_fn && errdes != STDERR_FILE_NO && close (errdes) < 0)
+	bad_fn = "close";
+
+      if (bad_fn)
+	{
+	  *err = errno;
+	  *errmsg = bad_fn;
+	  return (pid_t) -1;
 	}
 
       return pid;