On Sun, Jun 21, 2009 at 1:36 AM, Damjan Jovanovic <damjan.jov(a)gmail.com>wrote:
On Sun, Jun 21, 2009 at 1:06 AM, Erich Hoover<ehoover(a)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(a)mines.edu