From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2CA3FC433EF for ; Wed, 11 May 2022 14:46:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235614AbiEKOql (ORCPT ); Wed, 11 May 2022 10:46:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46230 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245016AbiEKOqU (ORCPT ); Wed, 11 May 2022 10:46:20 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 1A27E5FE6; Wed, 11 May 2022 07:46:17 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E7E4223A; Wed, 11 May 2022 07:46:16 -0700 (PDT) Received: from e121896.arm.com (unknown [10.57.2.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 3D0103F66F; Wed, 11 May 2022 07:46:15 -0700 (PDT) From: James Clark To: suzuki.poulose@arm.com, mathieu.poirier@linaro.org, coresight@lists.linaro.org, mike.leach@linaro.org Cc: leo.yan@linaro.com, James Clark , Leo Yan , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 4/4] Documentation: coresight: Expand branch broadcast documentation Date: Wed, 11 May 2022 15:46:01 +0100 Message-Id: <20220511144601.2257870-5-james.clark@arm.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20220511144601.2257870-1-james.clark@arm.com> References: <20220511144601.2257870-1-james.clark@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that there is a way of enabling branch broadcast via perf, mention the possible use cases and known limitations. Signed-off-by: James Clark --- .../trace/coresight/coresight-etm4x-reference.rst | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/Documentation/trace/coresight/coresight-etm4x-reference.rst b/Documentation/trace/coresight/coresight-etm4x-reference.rst index 0439b4006227..fb7578fd9372 100644 --- a/Documentation/trace/coresight/coresight-etm4x-reference.rst +++ b/Documentation/trace/coresight/coresight-etm4x-reference.rst @@ -656,7 +656,18 @@ Bit assignments shown below:- ETM_MODE_BB **description:** - Set to enable branch broadcast if supported in hardware [IDR0]. + Set to enable branch broadcast if supported in hardware [IDR0]. The primary use for this feature + is when code is patched dynamically at run time and the full program flow may not be able to be + reconstructed using only conditional branches. + + There is currently no support in Perf for supplying modified binaries to the decoder, so this + feature is only inteded to be used for debugging purposes or with a 3rd party tool. + + Choosing this option will result in a significant increase in the amount of trace generated - + possible danger of overflows, or fewer instructions covered. Note, that this option also + overrides any setting of :ref:`ETM_MODE_RETURNSTACK `, so where a branch + broadcast range overlaps a return stack range, return stacks will not be available for that + range. .. _coresight-cycle-accurate: -- 2.28.0