Re: [PATCH] Semihost SYS_READC implementation (v4)

[Peter Maydell]

On Thu, 14 Nov 2019 at 19:18, Richard Henderson
<address@hidden> wrote:
>   - If the sequence crosses a page, then so be it.  Because of
>     step 1, this only happens when we *must* cross a page, and
>     will have recognized any paging exception anyway.
>     The generic parts of qemu will handle proper invalidation of
>     a TB that crosses a page boundary.

I'm not sure this would work. If you have
  insn1 insn2 || other-insn
(where || is the page boundary and page 2 is non-executable)
then the required behaviour is "execute insn1 and insn2 with
normal behaviour, then fault trying to read other-insn, with
the fault address being that of other-insn".
Whereas for
  insn1 insn2 || insn3
you want to treat it as a semihosting sequence. But you can't distinguish
the two because trying to read the word in page 2 will cause us to
generate a fault with the fault address being that of insn1. Or
have I forgotten how the page-crossing handling works ?

thanks
-- PMM