Some analysis greatly benefits, or depends on, information about
certain types of dicontinuities such as interrupts. For example, we may
need to handle the execution of a new translation block differently if
it is not the result of normal program flow but of an interrupt.

Even with the existing interfaces, it is more or less possible to
discern these situations, e.g. as done by the cflow plugin. However,
this process poses a considerable overhead to the core analysis one may
intend to perform.

These changes introduce a generic and easy-to-use interface for plugin
authors in the form of a callback for discontinuities. Patch 1 defines
an enumeration of some trap-related discontinuities including somewhat
narrow definitions of the discontinuity evetns and a callback type.
Patch 2 defines the callback registration function. Patch 3 adds some
hooks for triggering the callbacks. Patch 4 adds an example plugin
showcasing the new API. Patches 5 through 6 call the hooks for a
selection of architectures, mapping architecture specific events to the
three categories defined in patch 1. Future non-RFC patchsets will call
these hooks for all architectures (that have some concept of trap or
interrupt). Finally, patch 11 supplies a test plugin asserting that the
next PC provided to the plugin points to the next instruction executed.

Sidenote: I'm likely doing something wrong for one architecture or
the other. These patches are untested for most of them.

Since v2 (tcg-plugins: add hooks for interrupts, exceptions and traps):
  - Switched from traps as core concept to more generic discontinuities
  - Switched from semihosting to hostcall as term for emulated traps
  - Added enumeration of events and dedicated callback type
  - Make callback receive event type as well as origin and target PC
    (as requested by Pierrick Bouvier)
  - Combined registration functions for different traps into a single
    one for all types of discontinuities (as requested by Pierrick
    Bouvier)
  - Migrated records in example plugin from fully pre-allocated to a
    scoreboard (as suggested by Pierrick Bouvier)
  - Handle PSCI calls as hostcall (as pointed out by Peter Maydell)
  - Added hooks for ARM Cortex M arches (as pointed out by Peter
    Maydell)
  - Added hooks for Alpha targets
  - Added hooks for MIPS targets
  - Added a plugin for testing some of the interface behaviour

Since v1:
  - Split the one callback into multiple callbacks
  - Added a target-agnostic definition of the relevant event(s)
  - Call hooks from architecture-code rather than accel/tcg/cpu-exec.c
  - Added a plugin showcasing API usage

Julian Ganz (11):
  plugins: add types for callbacks related to certain discontinuities
  plugins: add API for registering discontinuity callbacks
  plugins: add hooks for new discontinuity related callbacks
  contrib/plugins: add plugin showcasing new dicontinuity related API
  target/alpha: call plugin trap callbacks
  target/arm: call plugin trap callbacks
  target/avr: call plugin trap callbacks
  target/mips: call plugin trap callbacks
  target/riscv: call plugin trap callbacks
  target/sparc: call plugin trap callbacks
  tests: add plugin asserting correctness of discon event's to_pc

 contrib/plugins/meson.build         |  3 +-
 contrib/plugins/traps.c             | 96 +++++++++++++++++++++++++++++
 include/qemu/plugin-event.h         |  3 +
 include/qemu/plugin.h               | 13 ++++
 include/qemu/qemu-plugin.h          | 58 +++++++++++++++++
 plugins/core.c                      | 67 ++++++++++++++++++++
 target/alpha/helper.c               | 12 ++++
 target/arm/helper.c                 | 25 ++++++++
 target/arm/tcg/m_helper.c           | 18 ++++++
 target/avr/helper.c                 |  3 +
 target/mips/tcg/sysemu/tlb_helper.c | 11 ++++
 target/riscv/cpu_helper.c           |  9 +++
 target/sparc/int32_helper.c         |  7 +++
 target/sparc/int64_helper.c         | 10 +++
 tests/tcg/plugins/discons.c         | 95 ++++++++++++++++++++++++++++
 tests/tcg/plugins/meson.build       |  2 +-
 16 files changed, 430 insertions(+), 2 deletions(-)
 create mode 100644 contrib/plugins/traps.c
 create mode 100644 tests/tcg/plugins/discons.c

-- 
2.45.2

Hi,

I just realized that I forgot to run the checkpatch script on the
patches again before sending and did not include the Sign-Off. Sorry
about that.

Regards,
Julian Ganz

On 12/3/24 00:36, Julian Ganz wrote:
> Hi,
> 
> I just realized that I forgot to run the checkpatch script on the
> patches again before sending and did not include the Sign-Off. Sorry
> about that.
> 
> Regards,
> Julian Ganz
> 

No worries, it's pretty frequent that people forgot those.

While at it, you can fix the style issues checkpatch has reported for 
the series.

Julian Ganz <neither@nut.email> writes:

> Some analysis greatly benefits, or depends on, information about
> certain types of dicontinuities such as interrupts. For example, we may
> need to handle the execution of a new translation block differently if
> it is not the result of normal program flow but of an interrupt.
>
> Even with the existing interfaces, it is more or less possible to
> discern these situations, e.g. as done by the cflow plugin. However,
> this process poses a considerable overhead to the core analysis one may
> intend to perform.
>
> These changes introduce a generic and easy-to-use interface for plugin
> authors in the form of a callback for discontinuities. Patch 1 defines
> an enumeration of some trap-related discontinuities including somewhat
> narrow definitions of the discontinuity evetns and a callback type.
> Patch 2 defines the callback registration function. Patch 3 adds some
> hooks for triggering the callbacks. Patch 4 adds an example plugin
> showcasing the new API. Patches 5 through 6 call the hooks for a
> selection of architectures, mapping architecture specific events to the
> three categories defined in patch 1. Future non-RFC patchsets will call
> these hooks for all architectures (that have some concept of trap or
> interrupt). Finally, patch 11 supplies a test plugin asserting that the
> next PC provided to the plugin points to the next instruction executed.
>
> Sidenote: I'm likely doing something wrong for one architecture or
> the other. These patches are untested for most of them.

I've finished my review pass. Overall I think the API is fine but I
would like the arch maintainers to be happy the individual hooks capture
the right semantics for their arches.

I think Pierrick has already picked up some compile failures, you can
see more from my gitlab CI run:

  https://gitlab.com/stsquad/qemu/-/pipelines/1618014020

As you have discovered with the discontinuity issue making sure the
execution state is consistent with JIT'ed code has a few landmines in
it. Given it is hard to trigger with our basic softmmu tests you should
consider a few more aggressive tests like:

  tests/functional/test_aarch64_tcg_plugins.py

where we can pick exactly which plugin we want to use and run something
that will have a lot of IRQs and exceptions in it. It doesn't have to be
Aarch64 - whichever arch you are most familiar with. A test that
includes a hypervisor would be ideal as that will trigger a wider range
of execution state changes.

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro