c17a386b6a
We have an exploding complexity problem in the testing so lets just move the more involved plugins into contrib. tests/plugins still exist for the basic plugins that exercise the API. We restore the old pre-meson style Makefile for contrib as it also doubles as a guide for out-of-tree plugin builds. While we are at it add some examples to the documentation and a specific plugins build target. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Message-Id: <20200909112742.25730-11-alex.bennee@linaro.org>
283 lines
12 KiB
ReStructuredText
283 lines
12 KiB
ReStructuredText
..
|
|
Copyright (C) 2017, Emilio G. Cota <cota@braap.org>
|
|
Copyright (c) 2019, Linaro Limited
|
|
Written by Emilio Cota and Alex Bennée
|
|
|
|
================
|
|
QEMU TCG Plugins
|
|
================
|
|
|
|
QEMU TCG plugins provide a way for users to run experiments taking
|
|
advantage of the total system control emulation can have over a guest.
|
|
It provides a mechanism for plugins to subscribe to events during
|
|
translation and execution and optionally callback into the plugin
|
|
during these events. TCG plugins are unable to change the system state
|
|
only monitor it passively. However they can do this down to an
|
|
individual instruction granularity including potentially subscribing
|
|
to all load and store operations.
|
|
|
|
API Stability
|
|
=============
|
|
|
|
This is a new feature for QEMU and it does allow people to develop
|
|
out-of-tree plugins that can be dynamically linked into a running QEMU
|
|
process. However the project reserves the right to change or break the
|
|
API should it need to do so. The best way to avoid this is to submit
|
|
your plugin upstream so they can be updated if/when the API changes.
|
|
|
|
API versioning
|
|
--------------
|
|
|
|
All plugins need to declare a symbol which exports the plugin API
|
|
version they were built against. This can be done simply by::
|
|
|
|
QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
|
|
|
|
The core code will refuse to load a plugin that doesn't export a
|
|
`qemu_plugin_version` symbol or if plugin version is outside of QEMU's
|
|
supported range of API versions.
|
|
|
|
Additionally the `qemu_info_t` structure which is passed to the
|
|
`qemu_plugin_install` method of a plugin will detail the minimum and
|
|
current API versions supported by QEMU. The API version will be
|
|
incremented if new APIs are added. The minimum API version will be
|
|
incremented if existing APIs are changed or removed.
|
|
|
|
Exposure of QEMU internals
|
|
--------------------------
|
|
|
|
The plugin architecture actively avoids leaking implementation details
|
|
about how QEMU's translation works to the plugins. While there are
|
|
conceptions such as translation time and translation blocks the
|
|
details are opaque to plugins. The plugin is able to query select
|
|
details of instructions and system configuration only through the
|
|
exported *qemu_plugin* functions.
|
|
|
|
Query Handle Lifetime
|
|
---------------------
|
|
|
|
Each callback provides an opaque anonymous information handle which
|
|
can usually be further queried to find out information about a
|
|
translation, instruction or operation. The handles themselves are only
|
|
valid during the lifetime of the callback so it is important that any
|
|
information that is needed is extracted during the callback and saved
|
|
by the plugin.
|
|
|
|
Usage
|
|
=====
|
|
|
|
The QEMU binary needs to be compiled for plugin support::
|
|
|
|
configure --enable-plugins
|
|
|
|
Once built a program can be run with multiple plugins loaded each with
|
|
their own arguments::
|
|
|
|
$QEMU $OTHER_QEMU_ARGS \
|
|
-plugin tests/plugin/libhowvec.so,arg=inline,arg=hint \
|
|
-plugin tests/plugin/libhotblocks.so
|
|
|
|
Arguments are plugin specific and can be used to modify their
|
|
behaviour. In this case the howvec plugin is being asked to use inline
|
|
ops to count and break down the hint instructions by type.
|
|
|
|
Plugin Life cycle
|
|
=================
|
|
|
|
First the plugin is loaded and the public qemu_plugin_install function
|
|
is called. The plugin will then register callbacks for various plugin
|
|
events. Generally plugins will register a handler for the *atexit*
|
|
if they want to dump a summary of collected information once the
|
|
program/system has finished running.
|
|
|
|
When a registered event occurs the plugin callback is invoked. The
|
|
callbacks may provide additional information. In the case of a
|
|
translation event the plugin has an option to enumerate the
|
|
instructions in a block of instructions and optionally register
|
|
callbacks to some or all instructions when they are executed.
|
|
|
|
There is also a facility to add an inline event where code to
|
|
increment a counter can be directly inlined with the translation.
|
|
Currently only a simple increment is supported. This is not atomic so
|
|
can miss counts. If you want absolute precision you should use a
|
|
callback which can then ensure atomicity itself.
|
|
|
|
Finally when QEMU exits all the registered *atexit* callbacks are
|
|
invoked.
|
|
|
|
Internals
|
|
=========
|
|
|
|
Locking
|
|
-------
|
|
|
|
We have to ensure we cannot deadlock, particularly under MTTCG. For
|
|
this we acquire a lock when called from plugin code. We also keep the
|
|
list of callbacks under RCU so that we do not have to hold the lock
|
|
when calling the callbacks. This is also for performance, since some
|
|
callbacks (e.g. memory access callbacks) might be called very
|
|
frequently.
|
|
|
|
* A consequence of this is that we keep our own list of CPUs, so that
|
|
we do not have to worry about locking order wrt cpu_list_lock.
|
|
* Use a recursive lock, since we can get registration calls from
|
|
callbacks.
|
|
|
|
As a result registering/unregistering callbacks is "slow", since it
|
|
takes a lock. But this is very infrequent; we want performance when
|
|
calling (or not calling) callbacks, not when registering them. Using
|
|
RCU is great for this.
|
|
|
|
We support the uninstallation of a plugin at any time (e.g. from
|
|
plugin callbacks). This allows plugins to remove themselves if they no
|
|
longer want to instrument the code. This operation is asynchronous
|
|
which means callbacks may still occur after the uninstall operation is
|
|
requested. The plugin isn't completely uninstalled until the safe work
|
|
has executed while all vCPUs are quiescent.
|
|
|
|
Example Plugins
|
|
===============
|
|
|
|
There are a number of plugins included with QEMU and you are
|
|
encouraged to contribute your own plugins plugins upstream. There is a
|
|
`contrib/plugins` directory where they can go.
|
|
|
|
- tests/plugins
|
|
|
|
These are some basic plugins that are used to test and exercise the
|
|
API during the `make check-tcg` target.
|
|
|
|
- contrib/plugins/hotblocks.c
|
|
|
|
The hotblocks plugin allows you to examine the where hot paths of
|
|
execution are in your program. Once the program has finished you will
|
|
get a sorted list of blocks reporting the starting PC, translation
|
|
count, number of instructions and execution count. This will work best
|
|
with linux-user execution as system emulation tends to generate
|
|
re-translations as blocks from different programs get swapped in and
|
|
out of system memory.
|
|
|
|
If your program is single-threaded you can use the `inline` option for
|
|
slightly faster (but not thread safe) counters.
|
|
|
|
Example::
|
|
|
|
./aarch64-linux-user/qemu-aarch64 \
|
|
-plugin contrib/plugins/libhotblocks.so -d plugin \
|
|
./tests/tcg/aarch64-linux-user/sha1
|
|
SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
|
|
collected 903 entries in the hash table
|
|
pc, tcount, icount, ecount
|
|
0x0000000041ed10, 1, 5, 66087
|
|
0x000000004002b0, 1, 4, 66087
|
|
...
|
|
|
|
- contrib/plugins/hotpages.c
|
|
|
|
Similar to hotblocks but this time tracks memory accesses::
|
|
|
|
./aarch64-linux-user/qemu-aarch64 \
|
|
-plugin contrib/plugins/libhotpages.so -d plugin \
|
|
./tests/tcg/aarch64-linux-user/sha1
|
|
SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
|
|
Addr, RCPUs, Reads, WCPUs, Writes
|
|
0x000055007fe000, 0x0001, 31747952, 0x0001, 8835161
|
|
0x000055007ff000, 0x0001, 29001054, 0x0001, 8780625
|
|
0x00005500800000, 0x0001, 687465, 0x0001, 335857
|
|
0x0000000048b000, 0x0001, 130594, 0x0001, 355
|
|
0x0000000048a000, 0x0001, 1826, 0x0001, 11
|
|
|
|
- contrib/plugins/howvec.c
|
|
|
|
This is an instruction classifier so can be used to count different
|
|
types of instructions. It has a number of options to refine which get
|
|
counted. You can give an argument for a class of instructions to break
|
|
it down fully, so for example to see all the system registers
|
|
accesses::
|
|
|
|
./aarch64-softmmu/qemu-system-aarch64 $(QEMU_ARGS) \
|
|
-append "root=/dev/sda2 systemd.unit=benchmark.service" \
|
|
-smp 4 -plugin ./contrib/plugins/libhowvec.so,arg=sreg -d plugin
|
|
|
|
which will lead to a sorted list after the class breakdown::
|
|
|
|
Instruction Classes:
|
|
Class: UDEF not counted
|
|
Class: SVE (68 hits)
|
|
Class: PCrel addr (47789483 hits)
|
|
Class: Add/Sub (imm) (192817388 hits)
|
|
Class: Logical (imm) (93852565 hits)
|
|
Class: Move Wide (imm) (76398116 hits)
|
|
Class: Bitfield (44706084 hits)
|
|
Class: Extract (5499257 hits)
|
|
Class: Cond Branch (imm) (147202932 hits)
|
|
Class: Exception Gen (193581 hits)
|
|
Class: NOP not counted
|
|
Class: Hints (6652291 hits)
|
|
Class: Barriers (8001661 hits)
|
|
Class: PSTATE (1801695 hits)
|
|
Class: System Insn (6385349 hits)
|
|
Class: System Reg counted individually
|
|
Class: Branch (reg) (69497127 hits)
|
|
Class: Branch (imm) (84393665 hits)
|
|
Class: Cmp & Branch (110929659 hits)
|
|
Class: Tst & Branch (44681442 hits)
|
|
Class: AdvSimd ldstmult (736 hits)
|
|
Class: ldst excl (9098783 hits)
|
|
Class: Load Reg (lit) (87189424 hits)
|
|
Class: ldst noalloc pair (3264433 hits)
|
|
Class: ldst pair (412526434 hits)
|
|
Class: ldst reg (imm) (314734576 hits)
|
|
Class: Loads & Stores (2117774 hits)
|
|
Class: Data Proc Reg (223519077 hits)
|
|
Class: Scalar FP (31657954 hits)
|
|
Individual Instructions:
|
|
Instr: mrs x0, sp_el0 (2682661 hits) (op=0xd5384100/ System Reg)
|
|
Instr: mrs x1, tpidr_el2 (1789339 hits) (op=0xd53cd041/ System Reg)
|
|
Instr: mrs x2, tpidr_el2 (1513494 hits) (op=0xd53cd042/ System Reg)
|
|
Instr: mrs x0, tpidr_el2 (1490823 hits) (op=0xd53cd040/ System Reg)
|
|
Instr: mrs x1, sp_el0 (933793 hits) (op=0xd5384101/ System Reg)
|
|
Instr: mrs x2, sp_el0 (699516 hits) (op=0xd5384102/ System Reg)
|
|
Instr: mrs x4, tpidr_el2 (528437 hits) (op=0xd53cd044/ System Reg)
|
|
Instr: mrs x30, ttbr1_el1 (480776 hits) (op=0xd538203e/ System Reg)
|
|
Instr: msr ttbr1_el1, x30 (480713 hits) (op=0xd518203e/ System Reg)
|
|
Instr: msr vbar_el1, x30 (480671 hits) (op=0xd518c01e/ System Reg)
|
|
...
|
|
|
|
To find the argument shorthand for the class you need to examine the
|
|
source code of the plugin at the moment, specifically the `*opt`
|
|
argument in the InsnClassExecCount tables.
|
|
|
|
- contrib/plugins/lockstep.c
|
|
|
|
This is a debugging tool for developers who want to find out when and
|
|
where execution diverges after a subtle change to TCG code generation.
|
|
It is not an exact science and results are likely to be mixed once
|
|
asynchronous events are introduced. While the use of -icount can
|
|
introduce determinism to the execution flow it doesn't always follow
|
|
the translation sequence will be exactly the same. Typically this is
|
|
caused by a timer firing to service the GUI causing a block to end
|
|
early. However in some cases it has proved to be useful in pointing
|
|
people at roughly where execution diverges. The only argument you need
|
|
for the plugin is a path for the socket the two instances will
|
|
communicate over::
|
|
|
|
|
|
./sparc-softmmu/qemu-system-sparc -monitor none -parallel none \
|
|
-net none -M SS-20 -m 256 -kernel day11/zImage.elf \
|
|
-plugin ./contrib/plugins/liblockstep.so,arg=lockstep-sparc.sock \
|
|
-d plugin,nochain
|
|
|
|
which will eventually report::
|
|
|
|
qemu-system-sparc: warning: nic lance.0 has no peer
|
|
@ 0x000000ffd06678 vs 0x000000ffd001e0 (2/1 since last)
|
|
@ 0x000000ffd07d9c vs 0x000000ffd06678 (3/1 since last)
|
|
Δ insn_count @ 0x000000ffd07d9c (809900609) vs 0x000000ffd06678 (809900612)
|
|
previously @ 0x000000ffd06678/10 (809900609 insns)
|
|
previously @ 0x000000ffd001e0/4 (809900599 insns)
|
|
previously @ 0x000000ffd080ac/2 (809900595 insns)
|
|
previously @ 0x000000ffd08098/5 (809900593 insns)
|
|
previously @ 0x000000ffd080c0/1 (809900588 insns)
|
|
|