Re: questions on struct sigcontext

[David Daney <ddaney@avtrex.com>]

Chris Friesen wrote:
> Daniel Jacobowitz wrote:
> 
>> There used to be slots for badvaddr and cause.  You'll have to ask
>> Ralf why he decided to clobber them for DSP state, I don't remember
>> :-)  I suspect they may never have held useful information for you;
>> we don't context switch them for userspace, so an intervening fault
>> in kernel space or in another thread could change them.
> 
> I'm a bit confused as to how they would never have held useful 
> information--did you mean the registers themselves, or the entries in 
> struct sigcontext?

The entries in the sigcontext.  As Ralf said, they never held valid values.

> 
> If the cause/badvaddr entries in struct sigcontext were filled in by the 
> exception handler in the kernel,

It would appear that they are not.

> wouldn't the values in that struct be 
> completely valid even if the registers themselves were changed before 
> userspace could handle the signal?
> 
> If this is not the case then it seems like si_addr/si_code wouldn't be 
> trustworthy either.

This I am not sure about :(, However knowing the values of all registers 
(and perhaps /proc/self/maps) and $pc you can easily derive what happened.


David Daney