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a4023e02e8
COM32 binaries generally expect to run with interrupts
enabled. Syslinux does so, and COM32 programs will execute cli/sti
pairs when running a critical section, to provide mutual exclusion
against BIOS interrupt handlers. Previously, under iPXE, the IDT was
not valid, so any interrupt (e.g. a timer tick) would generally cause
the machine to triple fault.
This change introduces code to:
- Create a valid IDT at the same location that syslinux uses
- Create an "interrupt jump buffer", which contains small pieces of
code that simply record the vector number and jump to a common
handler
- Thunk down to real mode and execute the BIOS's interrupt handler
whenever an interrupt is received in a COM32 program
- Switch IDTs and enable/disable interrupts when context switching to
and from COM32 binaries
Testing done:
- Booted VMware ESX using a COM32 multiboot loader (mboot.c32)
- Built with GDBSERIAL enabled, and tested breakpoints on int22 and
com32_irq
- Put the following code in a COM32 program:
asm volatile ( "sti" );
while ( 1 );
Before this change, the machine would triple fault
immediately. After this change, it hangs as expected. Under Bochs,
it is possible to see the interrupt handler run, and the current
time in the BIOS data area gets incremented.
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
iPXE README File Quick start guide: cd src make For any more detailed instructions, see http://ipxe.org