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Date: Sat, 09 Apr 2016 17:05:40 +0200
From: "Juan Manuel Guerrero (juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
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To: djgpp AT delorie DOT com
Subject: Re: Different dup2 behaviour between DOS/DJGPP and posix.
References: <5706CAFA DOT 1060201 AT gmx DOT de> <5706E3D9 DOT 9070401 AT gmx DOT de>
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Reply-To: djgpp AT delorie DOT com

Am 08.04.2016 00:48, schrieb Juan Manuel Guerrero (juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com]:
> Am 07.04.2016 23:02, schrieb Juan Manuel Guerrero (juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com]:
> [snip]
>> The question is why DOS/DJGPP allows to close STDIN and reopen it with FD 0
>> meanwhile posix seems not to allow this. Is this behaviour expected?
>> I have inspected the code of dup2 and the implementation seems OK.
>>
>> The consequence of this check is that Autoconf assumes that DJGPP's dup2
>> implementaion does not work.
>
>
> OK I think I have got it. It is a bug in the DJGPP implementation of dup2.
> According to http://pubs.opengroup.org/onlinepubs/009695399/functions/dup.html
> The dup2() function shall fail if:
>
> [EBADF]
> The fildes argument is not a valid open file descriptor or the argument fildes2 is negative or greater than or equal to {OPEN_MAX}.
>
>
> The current implementation checks first if fd == newfd and if this is the case
> it returns inmediatly with newfd. Here some fix will be required because no one
> of the 3 conditions are checked. May be these error conditions were not in effect
> in those days when dup2 was implemented.
>
>
> Regards,
> Juan M. Guerrero


I have implemented a small fix that shall check for the validity of the
passed file descriptors to dup2.  This change should increase the posix
compliance of the dup2 implementation a little bit.  I have also added
a small check program that performs the same checks than the autoconf
check that called my attention to this issue.

As usual suggestions, objections and comments are welcome.  If I do not
get a response in a rasonable period of time I will commit the changes
to the repository.


Regards,
Juan M. Guerrero



2016-04-09  Juan Manuel Guerrero <juan DOT guerrero AT gmx DOT de>

	* djgpp/src/docs/kb/wc.txi:  Entry for wc206.txi added.

	* djgpp/src/docs/kb/wc205.txi:  Entry for wc206.txi added.

	* djgpp/src/docs/kb/wc206.txi:  Changes in DJGPP 2.06.

	* djgpp/src/libc/posix/unistd/dup2.c:  Check validity of passed file descriptors.

	* djgpp/src/libc/posix/unistd/dup2.txh:  Check validity of passed file descriptors.

	* djgpp/tests/libc/posix/unistd/dup2.c:  Check for dup2.

	* djgpp/tests/libc/posix/unistd/makefile:  Entry for dup2 added.





diff -aprNU7 djgpp.orig/src/docs/kb/wc.txi djgpp/src/docs/kb/wc.txi
--- djgpp.orig/src/docs/kb/wc.txi	2015-05-03 10:14:56 -0509
+++ djgpp/src/docs/kb/wc.txi	2016-04-09 14:04:10 -0509
@@ -1,18 +1,20 @@
  @node What Changed, Known Bugs, Introduction, Top
  @chapter What Changed

  @menu

-* Changes in 2.01::		DJGPP 2.01
-* Changes in 2.02::		DJGPP 2.02
-* Changes in 2.03::		DJGPP 2.03
-* Changes in 2.04::		DJGPP 2.04
-* Changes in 2.05::             DJGPP 2.05
+* Changes in 2.01::            DJGPP 2.01
+* Changes in 2.02::            DJGPP 2.02
+* Changes in 2.03::            DJGPP 2.03
+* Changes in 2.04::            DJGPP 2.04
+* Changes in 2.05::            DJGPP 2.05
+* Changes in 2.06::            DJGPP 2.06

  @end menu

  @include wc201.txi
  @include wc202.txi
  @include wc203.txi
  @include wc204.txi
  @include wc205.txi
+@include wc206.txi
diff -aprNU7 djgpp.orig/src/docs/kb/wc205.txi djgpp/src/docs/kb/wc205.txi
--- djgpp.orig/src/docs/kb/wc205.txi	2015-08-23 14:27:40 -0509
+++ djgpp/src/docs/kb/wc205.txi	2016-04-09 14:04:10 -0509
@@ -1,8 +1,8 @@
-@node Changes in 2.05, , Changes in 2.04, What Changed
+@node Changes in 2.05, Changes in 2.06, Changes in 2.04, What Changed
  @section Changes in 2.05

  Here is a list of changes from DJGPP V2.04 to DJGPP V2.05

  DJGPP v2.04 was actually never released and stayed in beta stage much too
  long.

diff -aprNU7 djgpp.orig/src/docs/kb/wc206.txi djgpp/src/docs/kb/wc206.txi
--- djgpp.orig/src/docs/kb/wc206.txi	1969-12-31 18:50:31 -0509
+++ djgpp/src/docs/kb/wc206.txi	2016-04-09 14:08:14 -0509
@@ -0,0 +1,12 @@
+@node Changes in 2.06, , Changes in 2.05, What Changed
+@section Changes in 2.06
+
+Here is a list of changes from DJGPP V2.05 to DJGPP V2.06
+
+@findex dup2 AT r{, and POSIX.1-2001 compliance}
+The validity of the file descriptors passed to @code{dup2} is now checked.
+If @var{existing_handle} is not a valid open file descriptor or
+if @var{new_handle} is out of the allowed range for file descriptors
+the call of @code{dup2} will fail and @code{errno} will be set to @code{EBADF}.
+With this adjustment, the @acronym{Posix} compliance of the @code{dup2} implementation
+is increasd.
diff -aprNU7 djgpp.orig/src/libc/posix/unistd/dup2.c djgpp/src/libc/posix/unistd/dup2.c
--- djgpp.orig/src/libc/posix/unistd/dup2.c	2001-08-19 16:50:26 -0509
+++ djgpp/src/libc/posix/unistd/dup2.c	2016-04-09 15:18:28 -0509
@@ -1,7 +1,8 @@
+/* Copyright (C) 2016 DJ Delorie, see COPYING.DJ for details */
  /* Copyright (C) 2001 DJ Delorie, see COPYING.DJ for details */
  /* Copyright (C) 1996 DJ Delorie, see COPYING.DJ for details */
  /* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */
  #include <libc/stubs.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <dpmi.h>
@@ -11,16 +12,24 @@
  #include <libc/dosio.h>
  #include <libc/fd_props.h>

  int
  dup2(int fd, int newfd)
  {
    __dpmi_regs r;
+
+  if (newfd < 0 || newfd >= getdtablesize() || _get_dev_info(fd) == -1)
+  {
+    errno = EBADF;
+    return -1;
+  }
+
    if (fd == newfd)
      return newfd;
+
    /* Reset the text/binary modes, the fsext, and the properties, since
       DOS function 46h closes newfd.  */
    __file_handle_set(newfd, __file_handle_modes[fd] ^ (O_BINARY|O_TEXT));
    __FSEXT_set_function(newfd, 0);
    r.h.ah = 0x46;
    r.x.bx = fd;
    r.x.cx = newfd;
diff -aprNU7 djgpp.orig/src/libc/posix/unistd/dup2.txh djgpp/src/libc/posix/unistd/dup2.txh
--- djgpp.orig/src/libc/posix/unistd/dup2.txh	2003-01-29 12:51:40 -0509
+++ djgpp/src/libc/posix/unistd/dup2.txh	2016-04-09 14:04:10 -0509
@@ -8,23 +8,25 @@
  int dup2(int existing_handle, int new_handle);
  @end example

  @subheading Description

  This call causes @var{new_handle} to refer to the same file and file
  pointer as @var{existing_handle}.  If @var{new_handle} is an open file,
-it is closed.
+it is closed.  If @var{existing_handle} is not a valid open file descriptor
+or if @var{new_handle} out of the allowed range for file descriptors the
+call will fail and @code{errno} will be set to @code{EBADF}.

  @subheading Return Value

  The new handle, or -1 on error.

  @subheading Portability

-@portability !ansi, posix
+@portability !ansi, posix-1003.1-2001

  @subheading Example

  @example
  /* copy new file to stdin stream */
  close(0);
  dup2(new_stdin, 0);
diff -aprNU7 djgpp.orig/tests/libc/posix/unistd/dup2.c djgpp/tests/libc/posix/unistd/dup2.c
--- djgpp.orig/tests/libc/posix/unistd/dup2.c	1969-12-31 18:50:31 -0509
+++ djgpp/tests/libc/posix/unistd/dup2.c	2016-04-09 16:10:50 -0509
@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <errno.h>
+#include <limits.h>
+#include <sys/resource.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+
+int main (void)
+{
+  int result = 0;
+  int bad_fd = INT_MAX;
+  struct rlimit rlim;
+
+
+  if (getrlimit(RLIMIT_NOFILE, &rlim) == 0
+      && 0 <= rlim.rlim_cur && rlim.rlim_cur <= INT_MAX)
+    bad_fd = rlim.rlim_cur;
+
+  if (dup2(1, 1) != 1)
+    result |= 1;
+
+  close (0);
+  if (dup2(0, 0) != -1)
+    result |= 2;
+
+  if (dup2(2, bad_fd) == -1 && errno != EBADF)
+    result |= 4;
+
+  if (dup2 (2, -1) != -1 && errno != EBADF)
+    result |= 8;
+
+  if (dup2(2, 254) != 254)
+    result |= 16;
+  if (dup2(2, 255) != -1)
+    result |= 32;
+
+  {
+    int fd = open(".", O_RDONLY);
+    if (fd == -1)
+      result |= 64;
+    else if (dup2(fd, fd + 1) == -1)
+      result |= 128;
+
+    close(fd);
+  }
+
+  if (result)
+    printf("dup2 check failed with result = %d\n", result);
+  else
+    printf("dup2 check passed.\n");
+
+  return result;
+}
+
diff -aprNU7 djgpp.orig/tests/libc/posix/unistd/makefile djgpp/tests/libc/posix/unistd/makefile
--- djgpp.orig/tests/libc/posix/unistd/makefile	2003-03-26 19:50:54 -0509
+++ djgpp/tests/libc/posix/unistd/makefile	2016-04-09 14:04:12 -0509
@@ -1,12 +1,13 @@
  TOP=../..

  SRC += access.c
  SRC += append.c
  SRC += chdr.c
+SRC += dup2.c
  SRC += gcwd.c
  SRC += getpid.c
  SRC += sleep.c
  SRC += tread.c
  SRC += write.c
  SRC += t-fchdir.c
  SRC += t-isatty.c