99a767c5d9
There's been a longstanding bug in the IRQ handling code in the Metalkit version of the SVGA reference driver, which occasionally caused tests to hang. I looked at the disassembly of SVGA_WaitForIRQ and friends, and I found one big problem and one smaller problem: The 'switchContext' flag is used to tell the IRQ handler whether it should branch to the saved context or not. This value *must* be written before we halt, or we can deadlock. Unfortunately, the value wasn't marked as 'volatile', and the compiler was optimizing out this assignment entirely! This means that 'flags' will never get set, and we'll be in an infinite loop. Given this bug, I'm not sure why WaitForIRQ ever worked. It's possible that we were fine if the IRQ had already arrived by the time WaitForIRQ was called, but we'd deadlock if we actually ended up waiting. If this is the case, it also means that fence-stress isn't doing a very good job of stressing the IRQ code. The other, much less severe problem: The stack frames for WaitForIRQInternal and SaveContext may have been partially overlapping, since gcc was allocating 0x10 bytes on the stack before calling SaveContext. The proper solution is probably just to rewrite all of this in assembly, but for now I just increased the number of padding words on the stack by adding extra NULL parameters to WaitForIRQInternal. |
||
|---|---|---|
| .. | ||
| metalkit | ||
| refdriver | ||
| util | ||
| vmware | ||
| Makefile.rules | ||
| README | ||
Library Code ------------ metalkit - Open source (MIT-licensed) library code for writing programs that run on the IA32 architecture on the "bare metal", without an operating system. refdriver - Source code for the VMware SVGA reference driver. util - Utility code used by the accompanying examples. Includes higher level APIs built on top of the reference driver, as well as miscellaneous code such as text rendering and matrix math. vmware - VMware-provided header files, including the headers which define registers and FIFO commands used by the VMware SVGA device. win32 - A Win32 port of the VMWare SVGA reference driver. This driver runs in userspace, using the kernel mode interface provided by VMware's proprietary kernel-mode graphics driver for Windows XP.