[{"id":4001,"web_url":"https://patchwork.libcamera.org/comment/4001/","msgid":"","date":"2020-03-07T23:37:21","subject":"Re: [libcamera-devel] [PATCH] libcamera: controls: Fix strict\n\taliasing violation","submitter":{"id":4,"url":"https://patchwork.libcamera.org/api/people/4/","name":"Kieran Bingham","email":"kieran.bingham@ideasonboard.com"},"content":"Hi Laurent,\n\nOn 07/03/2020 21:25, Laurent Pinchart wrote:\n> gcc 8.3.0 for ARM complains about strict aliasing violations:\n> \n> ../../src/libcamera/controls.cpp: In member function ‘void libcamera::ControlValue::release()’:\n> ../../src/libcamera/controls.cpp:111:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]\n> delete[] *reinterpret_cast(&storage_);\n> \n> Fix it and simplify the code at the same time.\n> \n> Signed-off-by: Laurent Pinchart \n\nFor either kept separate, or squashed into the other patch that adds this:\n\nReviewed-by: Kieran Bingham \n\nThough I wonder, could the above error also have been resolved with use\nof a uintptr_t?\n\nBut the union does seem to make the duality of use more clear to me all\nthe same.\n\n\n\n> ---\n> include/libcamera/controls.h | 5 ++++-\n> src/libcamera/controls.cpp | 20 ++++++++++----------\n> 2 files changed, 14 insertions(+), 11 deletions(-)\n> \n> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h\n> index 4767e2d3fc8c..0e111ab72bce 100644\n> --- a/include/libcamera/controls.h\n> +++ b/include/libcamera/controls.h\n> @@ -160,7 +160,10 @@ private:\n> \tControlType type_ : 8;\n> \tbool isArray_ : 1;\n> \tstd::size_t numElements_ : 16;\n> -\tuint64_t storage_;\n> +\tunion {\n> +\t\tuint64_t value_;\n> +\t\tvoid *storage_;\n> +\t};\n> \n> \tvoid release();\n> \tvoid set(ControlType type, bool isArray, const void *data,\n> diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp\n> index 94bdbdd9c388..4326174adf86 100644\n> --- a/src/libcamera/controls.cpp\n> +++ b/src/libcamera/controls.cpp\n> @@ -107,9 +107,9 @@ void ControlValue::release()\n> {\n> \tstd::size_t size = numElements_ * ControlValueSize[type_];\n> \n> -\tif (size > sizeof(storage_)) {\n> -\t\tdelete[] *reinterpret_cast(&storage_);\n> -\t\tstorage_ = 0;\n> +\tif (size > sizeof(value_)) {\n> +\t\tdelete[] reinterpret_cast(storage_);\n> +\t\tstorage_ = nullptr;\n> \t}\n> }\n> \n> @@ -176,9 +176,9 @@ ControlValue &ControlValue::operator=(const ControlValue &other)\n> Span ControlValue::data() const\n> {\n> \tstd::size_t size = numElements_ * ControlValueSize[type_];\n> -\tconst uint8_t *data = size > sizeof(storage_)\n> -\t\t\t ? *reinterpret_cast(&storage_)\n> -\t\t\t : reinterpret_cast(&storage_);\n> +\tconst uint8_t *data = size > sizeof(value_)\n> +\t\t\t ? reinterpret_cast(storage_)\n> +\t\t\t : reinterpret_cast(&value_);\n> \treturn { data, size };\n> }\n> \n> @@ -308,11 +308,11 @@ void ControlValue::set(ControlType type, bool isArray, const void *data,\n> \tstd::size_t size = elementSize * numElements;\n> \tvoid *storage;\n> \n> -\tif (size > sizeof(storage_)) {\n> -\t\tstorage = reinterpret_cast(new char[size]);\n> -\t\t*reinterpret_cast(&storage_) = storage;\n> +\tif (size > sizeof(value_)) {\n> +\t\tstorage_ = reinterpret_cast(new uint8_t[size]);\n> +\t\tstorage = storage_;\n> \t} else {\n> -\t\tstorage = reinterpret_cast(&storage_);\n> +\t\tstorage = reinterpret_cast(&value_);\n> \t}\n> \n> \tmemcpy(storage, data, size);\n>","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 9466360424\n\tfor ;\n\tSun, 8 Mar 2020 00:37:24 +0100 (CET)","from [192.168.0.20]\n\t(cpc89242-aztw30-2-0-cust488.18-1.cable.virginm.net [86.31.129.233])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id F08215F;\n\tSun, 8 Mar 2020 00:37:23 +0100 (CET)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1583624244;\n\tbh=eN3Sjuv4j+i76Qafdil/EqZVRcWfb3YnkdPvInmjY/g=;\n\th=Reply-To:Subject:To:References:From:Date:In-Reply-To:From;\n\tb=Vtk9gi7NkDkDiiG88tyMmde8X4SqkeidalbhZ9OwXizf+xkoow8gaWacRBPgHWdeC\n\tdIfs265mevrsl3oSI408xHzWtxIoug3XHonrXLzvR7+7EzlZYzD1oxM9oR+t8KRahX\n\twRaVINWXL71DJgM8jiplDSeA37Yo9OspBvNoHHq0=","Reply-To":"kieran.bingham@ideasonboard.com","To":"Laurent Pinchart ,\n\tlibcamera-devel@lists.libcamera.org","References":"<20200307212530.28053-3-laurent.pinchart@ideasonboard.com>","From":"Kieran Bingham ","Openpgp":"preference=signencrypt","Autocrypt":"addr=kieran.bingham@ideasonboard.com; keydata=\n\tmQINBFYE/WYBEACs1PwjMD9rgCu1hlIiUA1AXR4rv2v+BCLUq//vrX5S5bjzxKAryRf0uHat\n\tV/zwz6hiDrZuHUACDB7X8OaQcwhLaVlq6byfoBr25+hbZG7G3+5EUl9cQ7dQEdvNj6V6y/SC\n\trRanWfelwQThCHckbobWiQJfK9n7rYNcPMq9B8e9F020LFH7Kj6YmO95ewJGgLm+idg1Kb3C\n\tpotzWkXc1xmPzcQ1fvQMOfMwdS+4SNw4rY9f07Xb2K99rjMwZVDgESKIzhsDB5GY465sCsiQ\n\tcSAZRxqE49RTBq2+EQsbrQpIc8XiffAB8qexh5/QPzCmR4kJgCGeHIXBtgRj+nIkCJPZvZtf\n\tKr2EAbc6tgg6DkAEHJb+1okosV09+0+TXywYvtEop/WUOWQ+zo+Y/OBd+8Ptgt1pDRyOBzL8\n\tRXa8ZqRf0Mwg75D+dKntZeJHzPRJyrlfQokngAAs4PaFt6UfS+ypMAF37T6CeDArQC41V3ko\n\tlPn1yMsVD0p+6i3DPvA/GPIksDC4owjnzVX9kM8Zc5Cx+XoAN0w5Eqo4t6qEVbuettxx55gq\n\t8K8FieAjgjMSxngo/HST8TpFeqI5nVeq0/lqtBRQKumuIqDg+Bkr4L1V/PSB6XgQcOdhtd36\n\tOe9X9dXB8YSNt7VjOcO7BTmFn/Z8r92mSAfHXpb07YJWJosQOQARAQABtDBLaWVyYW4gQmlu\n\tZ2hhbSA8a2llcmFuLmJpbmdoYW1AaWRlYXNvbmJvYXJkLmNvbT6JAlcEEwEKAEECGwMFCwkI\n\tBwIGFQgJCgsCBBYCAwECHgECF4ACGQEWIQSQLdeYP70o/eNy1HqhHkZyEKRh/QUCXWTtygUJ\n\tCyJXZAAKCRChHkZyEKRh/f8dEACTDsbLN2nioNZMwyLuQRUAFcXNolDX48xcUXsWS2QjxaPm\n\tVsJx8Uy8aYkS85mdPBh0C83OovQR/OVbr8AxhGvYqBs3nQvbWuTl/+4od7DfK2VZOoKBAu5S\n\tQK2FYuUcikDqYcFWJ8DQnubxfE8dvzojHEkXw0sA4igINHDDFX3HJGZtLio+WpEFQtCbfTAG\n\tYZslasz1YZRbwEdSsmO3/kqy5eMnczlm8a21A3fKUo3g8oAZEFM+f4DUNzqIltg31OAB/kZS\n\tenKZQ/SWC8PmLg/ZXBrReYakxXtkP6w3FwMlzOlhGxqhIRNiAJfXJBaRhuUWzPOpEDE9q5YJ\n\tBmqQL2WJm1VSNNVxbXJHpaWMH1sA2R00vmvRrPXGwyIO0IPYeUYQa3gsy6k+En/aMQJd27dp\n\taScf9am9PFICPY5T4ppneeJLif2lyLojo0mcHOV+uyrds9XkLpp14GfTkeKPdPMrLLTsHRfH\n\tfA4I4OBpRrEPiGIZB/0im98MkGY/Mu6qxeZmYLCcgD6qz4idOvfgVOrNh+aA8HzIVR+RMW8H\n\tQGBN9f0E3kfwxuhl3omo6V7lDw8XOdmuWZNC9zPq1UfryVHANYbLGz9KJ4Aw6M+OgBC2JpkD\n\thXMdHUkC+d20dwXrwHTlrJi1YNp6rBc+xald3wsUPOZ5z8moTHUX/uPA/qhGsbkCDQRWBP1m\n\tARAAzijkb+Sau4hAncr1JjOY+KyFEdUNxRy+hqTJdJfaYihxyaj0Ee0P0zEi35CbE6lgU0Uz\n\ttih9fiUbSV3wfsWqg1Ut3/5rTKu7kLFp15kF7eqvV4uezXRD3Qu4yjv/rMmEJbbD4cTvGCYI\n\td6MDC417f7vK3hCbCVIZSp3GXxyC1LU+UQr3fFcOyCwmP9vDUR9JV0BSqHHxRDdpUXE26Dk6\n\tmhf0V1YkspE5St814ETXpEus2urZE5yJIUROlWPIL+hm3NEWfAP06vsQUyLvr/GtbOT79vXl\n\tEn1aulcYyu20dRRxhkQ6iILaURcxIAVJJKPi8dsoMnS8pB0QW12AHWuirPF0g6DiuUfPmrA5\n\tPKe56IGlpkjc8cO51lIxHkWTpCMWigRdPDexKX+Sb+W9QWK/0JjIc4t3KBaiG8O4yRX8ml2R\n\t+rxfAVKM6V769P/hWoRGdgUMgYHFpHGSgEt80OKK5HeUPy2cngDUXzwrqiM5Sz6Od0qw5pCk\n\tNlXqI0W/who0iSVM+8+RmyY0OEkxEcci7rRLsGnM15B5PjLJjh1f2ULYkv8s4SnDwMZ/kE04\n\t/UqCMK/KnX8pwXEMCjz0h6qWNpGwJ0/tYIgQJZh6bqkvBrDogAvuhf60Sogw+mH8b+PBlx1L\n\toeTK396wc+4c3BfiC6pNtUS5GpsPMMjYMk7kVvEAEQEAAYkCPAQYAQoAJgIbDBYhBJAt15g/\n\tvSj943LUeqEeRnIQpGH9BQJdizzIBQkLSKZiAAoJEKEeRnIQpGH9eYgQAJpjaWNgqNOnMTmD\n\tMJggbwjIotypzIXfhHNCeTkG7+qCDlSaBPclcPGYrTwCt0YWPU2TgGgJrVhYT20ierN8LUvj\n\t6qOPTd+Uk7NFzL65qkh80ZKNBFddx1AabQpSVQKbdcLb8OFs85kuSvFdgqZwgxA1vl4TFhNz\n\tPZ79NAmXLackAx3sOVFhk4WQaKRshCB7cSl+RIng5S/ThOBlwNlcKG7j7W2MC06BlTbdEkUp\n\tECzuuRBv8wX4OQl+hbWbB/VKIx5HKlLu1eypen/5lNVzSqMMIYkkZcjV2SWQyUGxSwq0O/sx\n\tS0A8/atCHUXOboUsn54qdxrVDaK+6jIAuo8JiRWctP16KjzUM7MO0/+4zllM8EY57rXrj48j\n\tsbEYX0YQnzaj+jO6kJtoZsIaYR7rMMq9aUAjyiaEZpmP1qF/2sYenDx0Fg2BSlLvLvXM0vU8\n\tpQk3kgDu7kb/7PRYrZvBsr21EIQoIjXbZxDz/o7z95frkP71EaICttZ6k9q5oxxA5WC6sTXc\n\tMW8zs8avFNuA9VpXt0YupJd2ijtZy2mpZNG02fFVXhIn4G807G7+9mhuC4XG5rKlBBUXTvPU\n\tAfYnB4JBDLmLzBFavQfvonSfbitgXwCG3vS+9HEwAjU30Bar1PEOmIbiAoMzuKeRm2LVpmq4\n\tWZw01QYHU/GUV/zHJSFk","Organization":"Ideas on Board","Message-ID":"","Date":"Sat, 7 Mar 2020 23:37:21 +0000","User-Agent":"Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101\n\tThunderbird/60.9.1","MIME-Version":"1.0","In-Reply-To":"<20200307212530.28053-3-laurent.pinchart@ideasonboard.com>","Content-Type":"text/plain; charset=utf-8","Content-Language":"en-GB","Content-Transfer-Encoding":"8bit","Subject":"Re: [libcamera-devel] [PATCH] libcamera: controls: Fix strict\n\taliasing violation","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Sat, 07 Mar 2020 23:37:24 -0000"}},{"id":4003,"web_url":"https://patchwork.libcamera.org/comment/4003/","msgid":"<20200308000114.GE31018@pendragon.ideasonboard.com>","date":"2020-03-08T00:01:14","subject":"Re: [libcamera-devel] [PATCH] libcamera: controls: Fix strict\n\taliasing violation","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Kieran,\n\nOn Sat, Mar 07, 2020 at 11:37:21PM +0000, Kieran Bingham wrote:\n> On 07/03/2020 21:25, Laurent Pinchart wrote:\n> > gcc 8.3.0 for ARM complains about strict aliasing violations:\n> > \n> > ../../src/libcamera/controls.cpp: In member function ‘void libcamera::ControlValue::release()’:\n> > ../../src/libcamera/controls.cpp:111:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]\n> > delete[] *reinterpret_cast(&storage_);\n> > \n> > Fix it and simplify the code at the same time.\n> > \n> > Signed-off-by: Laurent Pinchart \n> \n> For either kept separate, or squashed into the other patch that adds this:\n> \n> Reviewed-by: Kieran Bingham \n> \n> Though I wonder, could the above error also have been resolved with use\n> of a uintptr_t?\n\nI don't think so. Strict aliasing means, in a nutshell, that the\ncompiler can assume that pointers to different types do not point to the\nsame memory. There's an exception for char * that can alias anything.\nThe aliasing rules allow for interesting optimisations, but can also\ncreate \"interesting\" behaviour.\n\n#include \n\nvoid foo(int *i, char *c)\n{\n\t*i = 0x42;\n\tc[0] = 0;\n\tc[1] = 1;\n\tc[2] = 2;\n\tc[3] = 3;\n\n\tstd::cout << std::hex << *i << std::endl;\n}\n\nvoid foo(int *i, short *s)\n{\n\t*i = 0x42;\n\ts[0] = 0;\n\ts[1] = 1;\n\n\tstd::cout << std::hex << *i << std::endl;\n}\n\nint main(int argc __attribute__((__unused__)), char *argv[] __attribute__((__unused__)))\n{\n\tint i = 0;\n\tshort *s = reinterpret_cast(&i);\n\tchar *c = reinterpret_cast(&i);\n\n\tfoo(&i, c);\n\tfoo(&i, s);\n\n\treturn 0;\n}\n\n$ g++ -W -Wall -O1 -o aliasing aliasing.cpp \n$ ./aliasing \n3020100\n10000\n$ g++ -W -Wall -O2 -o aliasing aliasing.cpp \n$ ./aliasing \n3020100\n42\n\nclang++ exhibits the same behaviour. No idea why neither prints any\nwarning in the above example though :-S\n\n> But the union does seem to make the duality of use more clear to me all\n> the same.\n\nI like the union better too.\n\n> > ---\n> > include/libcamera/controls.h | 5 ++++-\n> > src/libcamera/controls.cpp | 20 ++++++++++----------\n> > 2 files changed, 14 insertions(+), 11 deletions(-)\n> > \n> > diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h\n> > index 4767e2d3fc8c..0e111ab72bce 100644\n> > --- a/include/libcamera/controls.h\n> > +++ b/include/libcamera/controls.h\n> > @@ -160,7 +160,10 @@ private:\n> > \tControlType type_ : 8;\n> > \tbool isArray_ : 1;\n> > \tstd::size_t numElements_ : 16;\n> > -\tuint64_t storage_;\n> > +\tunion {\n> > +\t\tuint64_t value_;\n> > +\t\tvoid *storage_;\n> > +\t};\n> > \n> > \tvoid release();\n> > \tvoid set(ControlType type, bool isArray, const void *data,\n> > diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp\n> > index 94bdbdd9c388..4326174adf86 100644\n> > --- a/src/libcamera/controls.cpp\n> > +++ b/src/libcamera/controls.cpp\n> > @@ -107,9 +107,9 @@ void ControlValue::release()\n> > {\n> > \tstd::size_t size = numElements_ * ControlValueSize[type_];\n> > \n> > -\tif (size > sizeof(storage_)) {\n> > -\t\tdelete[] *reinterpret_cast(&storage_);\n> > -\t\tstorage_ = 0;\n> > +\tif (size > sizeof(value_)) {\n> > +\t\tdelete[] reinterpret_cast(storage_);\n> > +\t\tstorage_ = nullptr;\n> > \t}\n> > }\n> > \n> > @@ -176,9 +176,9 @@ ControlValue &ControlValue::operator=(const ControlValue &other)\n> > Span ControlValue::data() const\n> > {\n> > \tstd::size_t size = numElements_ * ControlValueSize[type_];\n> > -\tconst uint8_t *data = size > sizeof(storage_)\n> > -\t\t\t ? *reinterpret_cast(&storage_)\n> > -\t\t\t : reinterpret_cast(&storage_);\n> > +\tconst uint8_t *data = size > sizeof(value_)\n> > +\t\t\t ? reinterpret_cast(storage_)\n> > +\t\t\t : reinterpret_cast(&value_);\n> > \treturn { data, size };\n> > }\n> > \n> > @@ -308,11 +308,11 @@ void ControlValue::set(ControlType type, bool isArray, const void *data,\n> > \tstd::size_t size = elementSize * numElements;\n> > \tvoid *storage;\n> > \n> > -\tif (size > sizeof(storage_)) {\n> > -\t\tstorage = reinterpret_cast(new char[size]);\n> > -\t\t*reinterpret_cast(&storage_) = storage;\n> > +\tif (size > sizeof(value_)) {\n> > +\t\tstorage_ = reinterpret_cast(new uint8_t[size]);\n> > +\t\tstorage = storage_;\n> > \t} else {\n> > -\t\tstorage = reinterpret_cast(&storage_);\n> > +\t\tstorage = reinterpret_cast(&value_);\n> > \t}\n> > \n> > \tmemcpy(storage, data, size);","headers":{"Return-Path":"","Received":["from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 754D160424\n\tfor ;\n\tSun, 8 Mar 2020 01:01:18 +0100 (CET)","from pendragon.ideasonboard.com (81-175-216-236.bb.dnainternet.fi\n\t[81.175.216.236])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id D81A05F;\n\tSun, 8 Mar 2020 01:01:17 +0100 (CET)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1583625678;\n\tbh=MkhuQNuHX+Yt8qUfPqbsJnLL/yW1RDeotNcCauRuMw4=;\n\th=Date:From:To:Cc:Subject:References:In-Reply-To:From;\n\tb=Hl5eNn2m0fNuG8+ukVgliI9JQCLVdgybkAuwxcU4jLaIOOJzHlqmzxTYCJ64N7dLN\n\tk173Fba4UB2RUVAzfOGAH1UQDjdAR9fII9XpkqjXM36DnVhUtlqpzKF48nRt4cu1iq\n\t9u6GZ0L6KEc/dQgGJrHRplghIwrfDgsRw0uAJ0jw=","Date":"Sun, 8 Mar 2020 02:01:14 +0200","From":"Laurent Pinchart ","To":"Kieran Bingham ","Cc":"libcamera-devel@lists.libcamera.org","Message-ID":"<20200308000114.GE31018@pendragon.ideasonboard.com>","References":"<20200307212530.28053-3-laurent.pinchart@ideasonboard.com>\n\t","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","Content-Transfer-Encoding":"8bit","In-Reply-To":"","User-Agent":"Mutt/1.10.1 (2018-07-13)","Subject":"Re: [libcamera-devel] [PATCH] libcamera: controls: Fix strict\n\taliasing violation","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","X-List-Received-Date":"Sun, 08 Mar 2020 00:01:18 -0000"}}]