Re: [PATCH 03/16] exec: Add cpu_probe_watchpoint

[Peter Maydell]

On Wed, 11 Mar 2020 at 06:44, Richard Henderson
<address@hidden> wrote:
>
> Allow probing of a watchpoint *without* raising an exception.
> This is of most use for no-fault loads, which should indicate
> via some architectural means that the load did not occur.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  include/hw/core/cpu.h |  7 +++++++
>  exec.c                | 19 +++++++++++++++++++
>  2 files changed, 26 insertions(+)
>
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 73e9a869a4..8ec44267a4 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -1090,6 +1090,12 @@ static inline void cpu_check_watchpoint(CPUState *cpu, 
> vaddr addr, vaddr len,
>  {
>  }
>
> +static inline bool cpu_probe_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
> +                                        int flags)
> +{
> +    return false;
> +}
> +
>  static inline int cpu_watchpoint_address_matches(CPUState *cpu,
>                                                   vaddr addr, vaddr len)
>  {
> @@ -1104,6 +1110,7 @@ void cpu_watchpoint_remove_by_ref(CPUState *cpu, 
> CPUWatchpoint *watchpoint);
>  void cpu_watchpoint_remove_all(CPUState *cpu, int mask);
>  void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
>                            MemTxAttrs attrs, int flags, uintptr_t ra);
> +bool cpu_probe_watchpoint(CPUState *cpu, vaddr addr, vaddr len, int flags);

Could we have a doc comment for the new function?

>  int cpu_watchpoint_address_matches(CPUState *cpu, vaddr addr, vaddr len);
>  #endif
>
> diff --git a/exec.c b/exec.c
> index 0cc500d53a..2b8f601b9e 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2735,6 +2735,25 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, 
> vaddr len,
>      }
>  }
>
> +bool cpu_probe_watchpoint(CPUState *cpu, vaddr addr, vaddr len, int flags)
> +{
> +    CPUClass *cc = CPU_GET_CLASS(cpu);
> +    CPUWatchpoint *wp;
> +
> +    assert(tcg_enabled());
> +
> +    addr = cc->adjust_watchpoint_address(cpu, addr, len);
> +    QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
> +        if (watchpoint_address_matches(wp, addr, len) &&
> +            (wp->flags & flags) &&
> +            (!(wp->flags & BP_CPU) ||
> +             !cc->debug_check_watchpoint(cpu, wp))) {
> +            return true;
> +        }
> +    }
> +    return false;
> +}

Clearly the insn emulation needs to do the right thing for
guest architectural watchpoints, but should a gdb watchpoint
also affect no-fault-load behaviour? I suppose making them
both behave the same way is probably the least-surprising choice.

thanks
-- PMM