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Mon, 11 Mar 2019 10:55:58 -0700 (PDT) Subject: Re: [PATCH v2 4/4] kernel-shark: Fix a bug in KsPluginManager To: Slavomir Kaslev Cc: Yordan Karadzhov , Steven Rostedt , linux-trace-devel@vger.kernel.org References: <20190307154316.19194-1-ykaradzhov@vmware.com> <20190307154316.19194-5-ykaradzhov@vmware.com> <351105f9-557d-5a2d-99f1-0f93db2848be@gmail.com> From: "Yordan Karadzhov (VMware)" Message-ID: Date: Mon, 11 Mar 2019 19:55:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-trace-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org On 11.03.19 г. 15:44 ч., Slavomir Kaslev wrote: > On Mon, Mar 11, 2019 at 3:20 PM Yordan Karadzhov (VMware) > wrote: >> >> >> >> On 11.03.19 г. 14:09 ч., Slavomir Kaslev wrote: >>> On Thu, Mar 7, 2019 at 5:44 PM Yordan Karadzhov wrote: >>>> >>>> const char *lib = plugin.toStdString().c_str(); >>>> >>>> This line is a bad idea because the returned array may (will) be >>>> invalidated when the destructor of std::string is called. >>>> >>>> Signed-off-by: Yordan Karadzhov >>>> --- >>>> kernel-shark/src/KsUtils.cpp | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/kernel-shark/src/KsUtils.cpp b/kernel-shark/src/KsUtils.cpp >>>> index 34b2e2d..d7b1753 100644 >>>> --- a/kernel-shark/src/KsUtils.cpp >>>> +++ b/kernel-shark/src/KsUtils.cpp >>>> @@ -439,7 +439,7 @@ void KsPluginManager::registerFromList(kshark_context *kshark_ctx) >>>> >>>> auto lamRegUser = [&kshark_ctx](const QString &plugin) >>>> { >>>> - const char *lib = plugin.toStdString().c_str(); >>>> + const char *lib = plugin.toLocal8Bit().data(); >>>> kshark_register_plugin(kshark_ctx, lib); >>>> }; >>>> >>>> @@ -474,7 +474,7 @@ void KsPluginManager::unregisterFromList(kshark_context *kshark_ctx) >>>> >>>> auto lamUregUser = [&kshark_ctx](const QString &plugin) >>>> { >>>> - const char *lib = plugin.toStdString().c_str(); >>>> + const char *lib = plugin.toLocal8Bit().data(); >>>> kshark_unregister_plugin(kshark_ctx, lib); >>>> }; >>> >>> Doesn't the new version have the same problem with the temporary QByteArray? >>> >>> How about saving the data in a local std::string/QByteArray variable? >>> >>> std::string lib = plugin.toStdString(); >>> kshark_register_plugin(kshark_ctx, lib.c_str()); >>> >> >> Hi Slavi, >> >> As far I can understand toStdString() will create a fresh std::string >> and this string will has its own copy of the characters. However, this >> copy gets out-of-scope as soon as we hit the semicolon of the line. >> >> My understanding was that toLocal8Bit().data() makes no copy so the >> array will go out-of-scope only when the QString is destroyed. > > I did some digging into QString's implementation. From my reading of > the code, toLocal8Bit() calls into qt_convert_to_latin1()[1] which > does allocation, copying/transform-to-latin1 and returns the > QByteArray. So it seems that toLocal8Bit() is still making a copy. > > [1] https://github.com/qt/qtbase/blob/5.12/src/corelib/tools/qstring.cpp#L5275 > > Cheers, > Thanks a lot for investigating this! I think in this case it will be more appropriate if you sign the patch. cheers, Y. > -- Slavi > >> >> But anyway, your solution looks cleaner and safer. >> I will send another version of the patch. >> Thanks a lot! >> Y. >> >> >>> Thanks! >>> >>> >>> -- >>> Slavomir Kaslev >>> > > >