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From: "Eli Zaretskii (eliz AT gnu DOT org)" <djgpp AT delorie DOT com>
Subject: Re: New GDB versions and DJGPP (Was: ANNOUNCE: DJGPP 2.05 beta 1)
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> Date: Sun, 24 May 2015 11:17:27 +0300
> From: "Andris Pavenis (andris DOT pavenis AT iki DOT fi)" <djgpp AT delorie DOT com>
> 
> > So what and how goes wrong in the DJGPP build of GDB?  Can someone
> > with enough free time step through the go32 initialization, and see
> > what's wrong there?
> 
> Perhaps at least some hint could give GDB commit which caused that DJGPP port stopped to work (with 
> symptoms described earlier)
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=9b409511d07fe375284701af34909fb539029caf

Thanks!

Actually, it seems bd265cd0bde9e045ab5946532449430b66fe91ad, which is
a followup to the one you mentioned, is the bad commit.  It seems a
simple case of misunderstanding the API conventions of our read_child
and write_child.

Can you try the patch below?  If it fixes the problem, I will push it.

diff --git a/gdb/go32-nat.c b/gdb/go32-nat.c
index f3966cd..852473b 100644
--- a/gdb/go32-nat.c
+++ b/gdb/go32-nat.c
@@ -587,6 +587,13 @@
   else
     res = read_child (memaddr, readbuf, len);
 
+  /* read_child and write_child return zero on success, non-zero on
+     failure; adjust the result value to that.  */
+  if (res == 0)
+    res = len;
+  else
+    res = -1;
+
   if (res <= 0)
     return TARGET_XFER_E_IO;