[PATCH] covoar/Target_aarch64: Swap QEMU taken/not taken bits

[Joel Sherrill]

On Fri, Apr 16, 2021 at 2:33 PM Gedare Bloom <gedare at rtems.org> wrote:

> why this is needed?
>

Bizarrely, qemu-couverture does not consistently set the same bit in the
traces
for taken and not taken across architectures.

https://git.rtems.org/rtems-tools/tree/tester/covoar/qemu-traces.h#n93

/* _BLOCK means pc .. pc+size-1 was executed.  */
#define TRACE_OP_BLOCK 0x10     /* Block fully executed.  */
#define TRACE_OP_FAULT 0x20     /* Fault at pc.  */
#define TRACE_OP_BR0   0x01     /* Branch 0 taken at pc.  */
#define TRACE_OP_BR1   0x02


Some architectures have BR0 meaning taken, others are not taken.


There has been code dealing with this since the initial move

from my rtems-testing to rtems-tools. But honestly I don't

recall anything about the difference. This means it has been

this way in Couverture for at least 7 years.


I have asked Alex to file this as an issue/question with

Couverture on github. Along with a clear bug on SPARC where

some code is missed because we do system calls to disable

interrupts and other actions. They don't seem to report those

in the traces.


--joel


> On Fri, Apr 16, 2021 at 1:25 PM Alex White <alex.white at oarcorp.com> wrote:
> >
> > This overrides the `TargetBase` behavior to allow branches to be marked
> > correctly as either taken or not taken.
> >
> > Closes #4387
> > ---
> >  tester/covoar/Target_aarch64.cc | 11 +++++++++++
> >  tester/covoar/Target_aarch64.h  |  6 ++++++
> >  2 files changed, 17 insertions(+)
> >
> > diff --git a/tester/covoar/Target_aarch64.cc
> b/tester/covoar/Target_aarch64.cc
> > index 64472d6..4d16456 100644
> > --- a/tester/covoar/Target_aarch64.cc
> > +++ b/tester/covoar/Target_aarch64.cc
> > @@ -12,6 +12,7 @@
> >
> >  #include <rld.h>
> >
> > +#include "qemu-traces.h"
> >  #include "Target_aarch64.h"
> >
> >  namespace Target {
> > @@ -90,6 +91,16 @@ namespace Target {
> >      );
> >    }
> >
> > +  uint8_t Target_aarch64::qemuTakenBit()
> > +  {
> > +    return TRACE_OP_BR1;
> > +  }
> > +
> > +  uint8_t Target_aarch64::qemuNotTakenBit()
> > +  {
> > +    return TRACE_OP_BR0;
> > +  }
> > +
> >    TargetBase *Target_aarch64_Constructor(
> >      std::string          targetName
> >    )
> > diff --git a/tester/covoar/Target_aarch64.h
> b/tester/covoar/Target_aarch64.h
> > index 26fedb6..08bd1fb 100644
> > --- a/tester/covoar/Target_aarch64.h
> > +++ b/tester/covoar/Target_aarch64.h
> > @@ -54,6 +54,12 @@ namespace Target {
> >        const char* const instruction
> >      );
> >
> > +    /* Documentation inherited from base class */
> > +    uint8_t qemuTakenBit() override;
> > +
> > +    /* Documentation inherited from base class */
> > +    uint8_t qemuNotTakenBit() override;
> > +
> >    private:
> >
> >    };
> > --
> > 2.27.0
> >
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