[03/16] exec: Add cpu_probe_watchpoint

Message ID 20200311064420.30606-4-richard.henderson@linaro.org
State New
Headers show
Series
  • target/arm: sve load/store improvements
Related show

Commit Message

Richard Henderson March 11, 2020, 6:44 a.m.
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 <richard.henderson@linaro.org>

---
 include/hw/core/cpu.h |  7 +++++++
 exec.c                | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+)

-- 
2.20.1

Comments

Peter Maydell April 16, 2020, 12:08 p.m. | #1
On Wed, 11 Mar 2020 at 06:44, Richard Henderson
<richard.henderson@linaro.org> 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 <richard.henderson@linaro.org>

> ---

>  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
Richard Henderson April 18, 2020, 2:14 a.m. | #2
On 4/16/20 5:08 AM, Peter Maydell wrote:
>>  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);


Hah.  In the process of doing that, I notice that
cpu_watchpoint_address_matches actually does what I want.

I have added documentation for cpu_check_watchpoint and
cpu_watchpoint_address_matches and have dropped this new function.

> 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.


In both cases we need to interrupt the execution in order to actually honor the
watchpoint.  So yes, treating them the same seems the only reasonable way.


r~

Patch

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);
 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;
+}
+
 static MemTxResult flatview_read(FlatView *fv, hwaddr addr,
                                  MemTxAttrs attrs, void *buf, hwaddr len);
 static MemTxResult flatview_write(FlatView *fv, hwaddr addr, MemTxAttrs attrs,