[PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Kylie McClain]

From: Kylie McClain <somasis@exherbo.org>

Not all Linux libcs (ex. musl libc) support the functionality used
under this #ifdef.
---
 src/print.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/print.c b/src/print.c
index 2b53d75..331f3c4 100644
--- a/src/print.c
+++ b/src/print.c
@@ -775,7 +775,7 @@ debug_output_compilation_hack (bool x)
   print_output_debug_flag = x;
 }
 
-#if defined (GNU_LINUX)
+#if defined (__GLIBC__)
 
 /* This functionality is not vitally important in general, so we rely on
    non-portable ability to use stderr as lvalue.  */
-- 
2.7.4

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Paul Eggert]

Thanks for reporting that. I filed a bug report with a proposed patch here:

http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23173

Instead of disabling redirect-debugging-output, this patch ports it to 
systems like musl where stderr is not an lvalue. Please give it a try if 
you have the time. it's against master commit 
750e1e19429cd781e2e60b462d19ef827d4da943.

I haven't installed it into 'master' yet, to give Eli a heads-up about 
the impending change.

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Kylie McClain]

On Thu, Mar 31, 2016 at 4:37 PM, Paul Eggert <eggert@cs.ucla.edu> wrote:
> Thanks for reporting that. I filed a bug report with a proposed patch here:
>
> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23173
>
> Instead of disabling redirect-debugging-output, this patch ports it to
> systems like musl where stderr is not an lvalue. Please give it a try if you
> have the time. it's against master commit
> 750e1e19429cd781e2e60b462d19ef827d4da943.
>
> I haven't installed it into 'master' yet, to give Eli a heads-up about the
> impending change.

Works just fine! :)

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Eli Zaretskii]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Thu, 31 Mar 2016 13:37:31 -0700
> Cc: Kylie McClain <somasis@exherbo.org>
> 
> I haven't installed it into 'master' yet, to give Eli a heads-up about 
> the impending change.

Thanks.  I needed the additional patch below to get the patch to
compile (how do other ports get F_DUPFD_CLOEXEC?).

After that, temacs seems to hang during loadup.  Looks like it hangs
inside the libc function 'close'.  I don't have enough free time now
to do anything serious on master.  Hopefully, someone else will be
able to look into this, find out why it hangs, and suggest a remedy.


--- src/print.c~0	2016-04-01 09:32:53.060500000 +0300
+++ src/print.c	2016-04-01 09:36:24.591750000 +0300
@@ -38,6 +38,10 @@ along with GNU Emacs.  If not, see <http
 #include <float.h>
 #include <ftoastr.h>
 
+#ifdef WINDOWSNT
+#include <sys/socket.h>		/* for F_DUPFD_CLOEXEC */
+#endif
+
 struct terminal;
 
 /* Avoid actual stack overflow in print.  */

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Paul Eggert]

Eli Zaretskii wrote:
> Thanks.  I needed the additional patch below to get the patch to
> compile (how do other ports get F_DUPFD_CLOEXEC?).

<fcntl.h> defines it, perhaps via the gnulib replacement sourced in lib/fcntl.in.h.

> After that, temacs seems to hang during loadup.  Looks like it hangs
> inside the libc function 'close'.  I don't have enough free time now
> to do anything serious on master.

No rush. When you get time, if you happen to know who's calling 'close' I could 
ifdef that call out on MS-Windows.

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Eli Zaretskii]

> Cc: somasissounds@gmail.com, emacs-devel@gnu.org, somasis@exherbo.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Fri, 1 Apr 2016 00:46:52 -0700
> 
> > After that, temacs seems to hang during loadup.  Looks like it hangs
> > inside the libc function 'close'.  I don't have enough free time now
> > to do anything serious on master.
> 
> No rush. When you get time, if you happen to know who's calling 'close' I could 
> ifdef that call out on MS-Windows.

It turns out the call to dup2 with 2 identical arguments has a strange
side effect with MS implementation: the subsequent attempt to fclose
the corresponding stdio stream hangs.  I was unable to understand why
that happens, since according to my references, such a dup2 call
should just validate the original file descriptor and do nothing else.
But since we already have a sys_dup2 function that wraps the MS dup2,
I added a workaround there, see the patch below.

For the record, what init_standard_fds does is unnecessary on
MS-Windows, since we already have the equivalent code in init_ntproc
(for reasons explained in the comments there).  So an alternative
would be to make init_standard_fds a no-op for WINDOWSNT.  I preferred
to have less #ifdef's in mainline Emacs code, but if you think the
alternative is better, it's fine with me.

Btw, are changes like the one below safe?

     /* Manipulate tty.  */
     if (hide_char)
       {
  -      etty_valid = emacs_get_tty (fileno (stdin), &etty) == 0;
  +      etty_valid = emacs_get_tty (STDIN_FILENO, &etty) == 0;
	 if (etty_valid)
  -	set_binary_mode (fileno (stdin), O_BINARY);
  -      suppress_echo_on_tty (fileno (stdin));
  +	set_binary_mode (STDIN_FILENO, O_BINARY);
  +      suppress_echo_on_tty (STDIN_FILENO);
       }

Are we sure fileno(stdin) will necessarily return 0, what with all the
redirections and stuff?  Why not keep the original code?

So to sum it up, these additional changes are required for MS-Windows:

diff --git a/src/print.c b/src/print.c
index 2b53d75..ee60f57 100644
--- a/src/print.c
+++ b/src/print.c
@@ -38,6 +38,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <float.h>
 #include <ftoastr.h>
 
+#ifdef WINDOWSNT
+#include <sys/socket.h>		/* for F_DUPFD_CLOEXEC */
+#endif
+
 struct terminal;
 
 /* Avoid actual stack overflow in print.  */
diff --git a/src/w32.c b/src/w32.c
index 3f4ac88..94aa7d8 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -8181,17 +8181,33 @@ sys_dup2 (int src, int dst)
       return -1;
     }
 
-  /* make sure we close the destination first if it's a pipe or socket */
-  if (src != dst && fd_info[dst].flags != 0)
+  /* MS _dup2 seems to have weird side effect when invoked with 2
+     identical arguments: an attempt to fclose the corresponding stdio
+     stream after that hangs (we do close standard streams in
+     init_ntproc).  Attempt to avoid that by not calling _dup2 that
+     way: if SRC is valid, we know that dup2 should be a no-op, so do
+     nothing and return DST.  */
+  if (src == dst)
+    {
+      if ((HANDLE)_get_osfhandle (src) == INVALID_HANDLE_VALUE)
+	{
+	  errno = EBADF;
+	  return -1;
+	}
+      return dst;
+    }
+
+  /* Make sure we close the destination first if it's a pipe or socket.  */
+  if (fd_info[dst].flags != 0)
     sys_close (dst);
 
   rc = _dup2 (src, dst);
   if (rc == 0)
     {
-      /* duplicate our internal info as well */
+      /* Duplicate our internal info as well.  */
       fd_info[dst] = fd_info[src];
     }
-  return rc;
+  return rc == 0 ? dst : rc;
 }
 
 int

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Paul Eggert]

Eli Zaretskii wrote:

> Are we sure fileno(stdin) will necessarily return 0, what with all the
> redirections and stuff?

Yes.  The redirections in Emacs don't change the file descriptor numbers 
associated with stdin, stdout, and stderr.  They will always be 0, 1, and 2.

> Why not keep the original code?

It's a bit slower, and (more important) it leads the reader to wonder whether 
fileno (stdin) might not equal STDIN_FILENO.

Re: [PATCH] src/print.c: Check for __GLIBC__ rather than GNU_LINUX

[Paul Eggert]

On 04/02/2016 01:35 AM, Eli Zaretskii wrote:
> I preferred
> to have less #ifdef's in mainline Emacs code, but if you think the
> alternative is better, it's fine with me.

No, I also like keeping the mainline code simpler. I installed the patch 
with your additions; thanks.