Syscalls and RSE

[Christian Kandeler]

Hi,

I think I have spotted a problem with the Backing Store switch for syscalls.
In epc_syscall, no flushrs is done; instead, the number of dirty registers is 
saved. But isn't it necessary in this case to restore the RNAT register after 
setting the new BspStore?
Imagine the case where we enter the syscall with BSP > BspStore and the 
location of a NaT collection in between. In such a case a subsequent RSE 
store in the kernel will write a partly undefined value to the next NaT 
collection address in the kernel backing store. This value will later be 
copied to the user space backing store by ia64_flush_dirty(), which also 
increases the saved user space BspStore by the number of dirty registers. As 
a consequence, when the user space BspStore is restored in 
epc_syscall_return, BspLoad will point to a location above the invalid NaT 
collection, which will subsequently be restored by RSE loads in user space 
and potentially contaminate stacked registers with NaT bits (or erroneously 
remove NaT bits from registers that should have them, depending on which bits 
of the "undefined" value are 1).


Regards,
Christian Kandeler