Fix PR win32/24284: tcp_auto_retry doesn't work in MinGW

This was reported by Bernhard Wodok, along with a patch to fix the
issue.  I adjusted the patch a bit, and I'm submitting the patch on
his behalf.

According to Bernhard, the issue can be reproduced by doing:

  1. start gdb
  2. enter 'target remote :2345'
  3. observe that it throws a "connection refused" error immediately
  instead of waiting and throwing a timeout error

I.e., I believe it can be reproduced by our current tests, which is
why I'm not proposing any extra tests here (well, I don't use nor have
any Windows system to test this, so...).

The problem happens because, on ser-tcp:wait_for_connect, we call
'gdb_select' passing 0 as its first argument, which, when using MinGW,
ends up using the 'gdb_select' version from mingw-hdep.c, and when the
first argument is 0 this means that WaitForMultipleObjects will be
called with 0 as its first argument as well.  According to the MS API
docs, this is forbidden:

  https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-waitformultipleobjects

The proposed fix is simple: we just call Sleep when N == 0 (and when
TIMEOUT is non-NULL), and return 0.  It makes sense to me.

Both Bernhard and Paul Carroll confirmed that the fix works.  I'm
Cc'ing Bernhard in case you have any questions about the patch.

OK?

gdb/ChangeLog:
2019-08-29  Bernhard Wodok  <barto@gmx.net>
	    Sergio Durigan Junior  <sergiodj@redhat.com>

	PR win32/24284
	* mingw-hdep.c (gdb_select): Handle case when 'n' is zero.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index a82f7c64ae89e0972b5cb649c5015193527bd5d3..fba2f4a995ec12171b5f5855a6287e91f8f683b7 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2019-08-29  Bernhard Wodok  <barto@gmx.net>
+           Sergio Durigan Junior  <sergiodj@redhat.com>
+
+       PR win32/24284
+       * mingw-hdep.c (gdb_select): Handle case when 'n' is zero.
+
 2019-08-28  Andrew Burgess  <andrew.burgess@embecosm.com>
 
        * symtab.c (search_symbols): Don't include MODULE_DOMAIN symbols

diff --git a/gdb/mingw-hdep.c b/gdb/mingw-hdep.c
index 44fb22e9a161b1bceaaf2bf3b2de368acfe3a3a7..0af1b39acdcc9987a73669f9116d05474d843fc9 100644 (file)
--- a/gdb/mingw-hdep.c
+++ b/gdb/mingw-hdep.c
@@ -64,6 +64,17 @@ gdb_select (int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
   int num_ready;
   size_t indx;
 
+  if (n == 0)
+    {
+      /* The MS API says that the first argument to
+        WaitForMultipleObjects cannot be zero.  That's why we just
+        use a regular Sleep here.  */
+      if (timeout != NULL)
+       Sleep (timeout->tv_sec * 1000 + timeout->tv_usec / 1000);
+
+      return 0;
+    }
+
   num_ready = 0;
   num_handles = 0;
   num_scbs = 0;