Date: Sat, 02 Jun 2001 12:57:13 +0300
From: "Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Sender: halo1 AT zahav DOT net DOT il
To: djgpp-workers AT delorie DOT com
Message-Id: <3405-Sat02Jun2001125713+0300-eliz@is.elta.co.il>
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CC: sandmann AT clio DOT rice DOT edu (Charles Sandmann)
In-reply-to: <20010523195757.15393.qmail@tyr.diku.dk> (message from Morten
	Welinder on 23 May 2001 19:57:57 -0000)
Subject: Re: Crashes due to selector depletion
References: <4331-Wed23May2001214623+0300-eliz AT is DOT elta DOT co DOT il> <20010523195757 DOT 15393 DOT qmail AT tyr DOT diku DOT dk>
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> Date: 23 May 2001 19:57:57 -0000
> From: Morten Welinder <terra AT diku DOT dk>
> 
> Can't you just use the character-at-a-time int 0x21 service
> to print your message?  Not terrible efficient, but you are
> not looking for that here.

Does the following look right?  If no one objects, I will commit this.


--- src/libc/crt0/crt1.c~0	Thu Jun  3 13:27:36 1999
+++ src/libc/crt0/crt1.c	Sat Jun  2 12:29:32 2001
@@ -16,6 +16,7 @@
 #include <pc.h>
 #include <libc/bss.h>
 #include <fcntl.h>
+#include <unistd.h>
 #include <libc/environ.h>
 #include <dos.h> /* for _osmajor/_osminor */
 
@@ -45,8 +46,33 @@ setup_core_selector(void)
   int c = __dpmi_allocate_ldt_descriptors(1);
   if (c == -1)
   {
-    _dos_ds = 0;
-    return;
+    /* We cannot continue without a valid _dos_ds selector, since
+       setup_screens, called next, already uses it, and will crash
+       unless we do something.
+
+       The failure to allocate a descriptor is known to happen on
+       Windows, when a long nested job (e.g., large recursive
+       Makefile) is in progress, due to the fact that the Windows DPMI
+       host leaks descriptors.
+
+       So we want to print an error message and exit; but the tricky
+       part is that we cannot use the transfer buffer or any other
+       buffer in conventional memory, because we don't have a selector
+       for DOS memory.  That's why we use function 02 of Int 21h.
+       (The idea is due to Morten Welinder.)  */
+    static const char no_dos_ds_msg[] =
+      "Cannot allocate selector for conventional memory; exiting\r\n";
+    const char *p = no_dos_ds_msg;
+    __dpmi_regs r;
+
+    r.h.ah = 2;
+    while (*p)
+    {
+      r.h.dl = *p & 0xff;
+      __dpmi_int(0x21, &r);
+      p++;
+    }
+    __exit(107);  /* the same error code stub.asm uses for no selectors */
   }
   _dos_ds = c;