Re: [Qemu-arm] [Qemu-devel] [PATCH 3/7] target/arm: Add ignore_stackfaults argument to v7m_exception_taken()

[Richard Henderson]

On 01/30/2018 07:02 AM, Peter Maydell wrote:
> In the v8M architecture, if the process of taking an exception
> results in a further exception this is called a derived exception
> (for example, an MPU exception when writing the exception frame to
> memory). If the derived exception happens while pushing the initial
> stack frame, we must ignore any subsequent possible exception
> pushing the callee-saves registers.
> 
> In preparation for making the stack writes check for exceptions,
> add a return value from v7m_push_stack() and a new parameter to
> v7m_exception_taken(), so that the former can tell the latter that
> it needs to ignore failures to write to the stack. We also plumb
> the argument through to v7m_push_callee_stack(), which is where
> the code to ignore the failures will be.
> 
> (Note that the v8M ARM pseudocode structures this slightly differently:
> derived exceptions cause the attempt to process the original
> exception to be abandoned; then at the top level it calls
> DerivedLateArrival to prioritize the derived exception and call
> TakeException from there. We choose to let the NVIC do the prioritization
> and continue forward with a call to TakeException which will then
> take either the original or the derived exception. The effect is
> the same, but this structure works better for QEMU because we don't
> have a convenient top level place to do the abandon-and-retry logic.)
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  target/arm/helper.c | 35 +++++++++++++++++++++++------------
>  1 file changed, 23 insertions(+), 12 deletions(-)

Reviewed-by: Richard Henderson <address@hidden>


r~