On Sun, Jun 21, 2009 at 1:36 AM, Damjan Jovanovic <damjan.jov@gmail.com> wrote:
On Sun, Jun 21, 2009 at 1:06 AM, Erich Hoover<ehoover@mines.edu> wrote:
> I'm trying to track down an issue with Launchpad Enhanced were it fails to
> download its updates (Bug #17443).  It appears that the issue stems from
> recv being called with a buffer from a different process, so as a result the
> call fails.  I put together a hack that gets around the problem
> (http://bugs.winehq.org/show_bug.cgi?id=17443#c2), but I'm having difficulty
> figuring out exactly why this is happening in the first place.  Does anyone
> know if this is a known difference between Windows and Linux or if there is
> something else strange going on?

If recv() fails with EFAULT, why doesn't the memcpy() in your patch
raise SIGSEGV instead?

While I realize now that I didn't exactly state this, that's why I thought the issue I was encountering was strange.


Maybe the memory is writable but not readable, and
WSARecvFrom()/recv() is reading it while memcpy() is not? 

Maybe the memory is from a DIB section which Wine lazily mprotects and
the kernel isn't raising SIGSEGV for the protection to be reapplied?
Does simply zero-filling buf before calling WSARecvFrom() help?

The memory should be a buffer from the calling application that it is using temporarily to store update data before saving it to the hard-disk.  Yes, oddly enough zero-filling the buffer before calling WSARecvFrom() also fixes the problem.

So, where exactly should I be looking to find the real problem?  As far as I can tell the memory for the buffer is being allocated immediate prior to the call and the request is for read/write access:
0009:Call KERNEL32.VirtualAlloc(01b85000,00040000,00001000,00000004) ret=79e74a2b
0009:Ret  KERNEL32.VirtualAlloc() retval=01b85000 ret=79e74a2b
0009:Call ws2_32.recv(00000380,01ba4fc1,000178d0,00000000) ret=0036a287
...

Erich Hoover
ehoover@mines.edu