Re: [gdbserver] Problems trying to resume dead threads

["Ulrich Weigand" <uweigand@de.ibm.com>]

Daniel Jacobowitz wrote:
> On Mon, Aug 04, 2008 at 09:45:46PM +0200, Ulrich Weigand wrote:
> > I'd propose to just silently ignore ESRCH errors while writing registers
> > (in addition to your patch).  What do you think?
> 
> I think that's acceptable, though not ideal.  ESRCH can mean "the
> program is gone", or for ptrace it can mean "the program is not
> stopped".  So there are a class of bugs in gdbserver which can lead to
> the ESRCH error path.  But distinguishing them from this case is quite
> difficult.

The following patch implements this approach, fixing the problem for me.
Tested on powerpc-linux in local gdbserver mode.  OK?

Bye,
Ulrich

ChangeLog:

	* linux-low.c (linux_resume_one_process): Ignore ESRCH.
	(usr_store_inferior_registers): Likewise.
	(regsets_store_inferior_registers): Likewise.


diff -urNp src-orig/gdb/gdbserver/linux-low.c src/gdb/gdbserver/linux-low.c
--- src-orig/gdb/gdbserver/linux-low.c	2008-08-05 19:44:47.000000000 +0200
+++ src/gdb/gdbserver/linux-low.c	2008-08-05 19:53:44.000000000 +0200
@@ -1195,7 +1195,19 @@ linux_resume_one_process (struct inferio
 
   current_inferior = saved_inferior;
   if (errno)
-    perror_with_name ("ptrace");
+    {
+      /* ESRCH from ptrace either means that the thread was already
+	 running (an error) or that it is gone (a race condition).  If
+	 it's gone, we will get a notification the next time we wait,
+	 so we can ignore the error.  We could differentiate these
+	 two, but it's tricky without waiting; the thread still exists
+	 as a zombie, so sending it signal 0 would succeed.  So just
+	 ignore ESRCH.  */
+      if (errno == ESRCH)
+	return;
+
+      perror_with_name ("ptrace");
+    }
 }
 
 static struct thread_resume *resume_ptr;
@@ -1464,6 +1476,12 @@ usr_store_inferior_registers (int regno)
 		  *(PTRACE_XFER_TYPE *) (buf + i));
 	  if (errno != 0)
 	    {
+	      /* At this point, ESRCH should mean the process is already gone, 
+		 in which case we simply ignore attempts to change its registers.
+		 See also the related comment in linux_resume_one_process.  */
+	      if (errno == ESRCH)
+		return;
+
 	      if ((*the_low_target.cannot_store_register) (regno) == 0)
 		{
 		  char *err = strerror (errno);
@@ -1580,6 +1598,13 @@ regsets_store_inferior_registers ()
 	      disabled_regsets[regset - target_regsets] = 1;
 	      continue;
 	    }
+	  else if (errno == ESRCH)
+	    {
+	      /* At this point, ESRCH should mean the process is already gone, 
+		 in which case we simply ignore attempts to change its registers.
+		 See also the related comment in linux_resume_one_process.  */
+	      return 0;
+	    }
 	  else
 	    {
 	      perror ("Warning: ptrace(regsets_store_inferior_registers)");


-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com