[{"id":3243857,"web_url":"http://patchwork.ozlabs.org/comment/3243857/","msgid":"<8ce7c705-8f11-4ed0-ba7c-7965a1dd1fff@linaro.org>","list_archive_url":null,"date":"2024-01-09T14:28:17","subject":"Re: [PATCH v2 43/43] docs/devel: document some plugin assumptions","submitter":{"id":85798,"url":"http://patchwork.ozlabs.org/api/people/85798/","name":"Pierrick Bouvier","email":"pierrick.bouvier@linaro.org"},"content":"Reviewed-by: Pierrick Bouvier \n\nOn 1/3/24 21:33, Alex Bennée wrote:\n> While we attempt to hide implementation details from the plugin we\n> shouldn't be totally obtuse. Let the user know what they can and can't\n> expect with the various instrumentation options.\n> \n> Signed-off-by: Alex Bennée \n> ---\n> docs/devel/tcg-plugins.rst | 49 ++++++++++++++++++++++++++++++++++++++\n> 1 file changed, 49 insertions(+)\n> \n> diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst\n> index 535a74684c5..9cc09d8c3da 100644\n> --- a/docs/devel/tcg-plugins.rst\n> +++ b/docs/devel/tcg-plugins.rst\n> @@ -112,6 +112,55 @@ details are opaque to plugins. The plugin is able to query select\n> details of instructions and system configuration only through the\n> exported *qemu_plugin* functions.\n> \n> +However the following assumptions can be made:\n> +\n> +Translation Blocks\n> +++++++++++++++++++\n> +\n> +All code will go through a translation phase although not all\n> +translations will be necessarily be executed. You need to instrument\n> +actual executions to track what is happening.\n> +\n> +It is quite normal to see the same address translated multiple times.\n> +If you want to track the code in system emulation you should examine\n> +the underlying physical address (``qemu_plugin_insn_haddr``) to take\n> +into account the effects of virtual memory although if the system does\n> +paging this will change too.\n> +\n> +Not all instructions in a block will always execute so if its\n> +important to track individual instruction execution you need to\n> +instrument them directly. However asynchronous interrupts will not\n> +change control flow mid-block.\n> +\n> +Instructions\n> +++++++++++++\n> +\n> +Instruction instrumentation runs before the instruction executes. You\n> +can be can be sure the instruction will be dispatched, but you can't\n> +be sure it will complete. Generally this will be because of a\n> +synchronous exception (e.g. SIGILL) triggered by the instruction\n> +attempting to execute. If you want to be sure you will need to\n> +instrument the next instruction as well. See the ``execlog.c`` plugin\n> +for examples of how to track this and finalise details after execution.\n> +\n> +Memory Accesses\n> ++++++++++++++++\n> +\n> +Memory callbacks are called after a successful load or store.\n> +Unsuccessful operations (i.e. faults) will not be visible to memory\n> +instrumentation although the execution side effects can be observed\n> +(e.g. entering a exception handler).\n> +\n> +System Idle and Resume States\n> ++++++++++++++++++++++++++++++\n> +\n> +The ``qemu_plugin_register_vcpu_idle_cb`` and\n> +``qemu_plugin_register_vcpu_resume_cb`` functions can be used to track\n> +when CPUs go into and return from sleep states when waiting for\n> +external I/O. Be aware though that these may occur less frequently\n> +than in real HW due to the inefficiencies of emulation giving less\n> +chance for the CPU to idle.\n> +\n> Internals\n> ---------\n>","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=G9tfFnVE;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4T8YGH1PJfz1yP7\n\tfor ; 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Iglesias\" ,\n Eduardo Habkost , qemu-riscv@nongnu.org,\n Alistair Francis ","References":"<20240103173349.398526-1-alex.bennee@linaro.org>\n <20240103173349.398526-44-alex.bennee@linaro.org>","From":"Pierrick Bouvier ","In-Reply-To":"<20240103173349.398526-44-alex.bennee@linaro.org>","Content-Type":"text/plain; charset=UTF-8; format=flowed","Content-Transfer-Encoding":"base64","Received-SPF":"pass client-ip=2a00:1450:4864:20::435;\n envelope-from=pierrick.bouvier@linaro.org; helo=mail-wr1-x435.google.com","X-Spam_score_int":"-20","X-Spam_score":"-2.1","X-Spam_bar":"--","X-Spam_report":"(-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001,\n T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"}}]