From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id 202113944419 for ; Tue, 19 Jan 2021 19:38:08 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 202113944419 Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-11-a9Xek0qXNoyjshGwQiFFjA-1; Tue, 19 Jan 2021 14:38:05 -0500 X-MC-Unique: a9Xek0qXNoyjshGwQiFFjA-1 Received: by mail-qk1-f199.google.com with SMTP id v82so464673qka.1 for ; Tue, 19 Jan 2021 11:38:05 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:cc:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=/y75yJD8+7vgxnIHpVXH2TNOCOVazcHtpe3nQhEOH3Y=; b=D6UU1BExq1Ro9nLymkNTmM+fjGhnhOmlNyQi5uSKMfPtMQVvPSvXZRpyyhsGoM87hu A4gW9oks0s5Izxsq8oqX1R3UP3u9b3udfJduuIsMdqZWn6afLK5EWF1B2pZzWe/ZfMfA 0UXOl8ZvXqs1nyVdAevRnXvDKlN4cLT3CDUHlCFjBkn/0nKwZSj9y5GcARqCSWA6wBRF PnAG2oRgT9a+ZUDP1qD+QPxQ0O51YfHmoNHxgJjM/5R2AzcXsaWWFwcXQQC1iag0DBQO lhvwONp9YtWOhnorj/XN2ai3fnncnGqUB2H/4J9mBOINFqhIZxxS6gCiUqAWYMYlmOOj pQIA== X-Gm-Message-State: AOAM533wAPCwe9t9SS8i/8FKwzzJgbXXkqlCQRkRdVjiNLPOal4BSxV6 AkmicxrCtjeC4jnMwUfuKQMsgfbm9X4DX9TsUwRkWFXwKEBCuJTeDSBF8HK4gm39aUa8UrOSLsv Xq3gPKY8VlCeI+HNkdyh3HuDtkofCrbVSQCyFSY0NkFR9AFpSAz1QYqTrWXtsgEi7Yg== X-Received: by 2002:a0c:fdec:: with SMTP id m12mr6178085qvu.11.1611085084947; Tue, 19 Jan 2021 11:38:04 -0800 (PST) X-Google-Smtp-Source: ABdhPJyLjGwDPKjgh89Y2idnntf8IwgCeQn0KOTweWQa+nGqcRQw8Jql8BO4jnL0zgq5nu+tWscL1w== X-Received: by 2002:a0c:fdec:: with SMTP id m12mr6178066qvu.11.1611085084693; Tue, 19 Jan 2021 11:38:04 -0800 (PST) Received: from [192.168.86.23] ([136.56.129.226]) by smtp.gmail.com with ESMTPSA id i17sm13062827qtg.77.2021.01.19.11.38.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Jan 2021 11:38:04 -0800 (PST) Subject: Re: stap --dyninst with C++ applications To: Siva N References: Cc: systemtap@sourceware.org From: Stan Cox Message-ID: <9e49ec35-f18b-2a52-39c9-4be844905ed8@redhat.com> Date: Tue, 19 Jan 2021 14:38:03 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-3.2 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, NICE_REPLY_A, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: systemtap@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Systemtap mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Jan 2021 19:38:09 -0000 > I am curious to understand how C++ object arguments are handled with USDT. > > I have a C++ application. I have added probe points using the DTRACE_PROBE[n] macro. If I pass a reference/pointer to a C++ object as one of the arguments, I wonder how one accesses this inside the probe handler. I could treat the argument(s) as a void pointer, and if I managed create the actual C++ object layout --dyninst should handle probe("NAME").mark("LABEL") probes fine. If I have the small c++ sample: > #include > #include > #include > using namespace std; > > struct A > { > A(); > long aa; > long bb; > string string1; > string string2; > }; > > A::A () > { > aa = 10; > bb = 20; > string1 = "abc"; > string2 = "xyz"; > } > > int main() > { > struct A anA; > SDT_MISC_TEST_PROBE_4(&anA); > std::cout << anA.aa << ' ' << anA.bb << ' ' << anA.string1 << ' ' << anA.string2 << ' ' << '\n'; > } and the .d file: > provider sdt_misc { > probe test_probe_4 (struct A arg); > }; Then the arg struct corresponding to SDT_MISC_TEST_PROBE_4 can be accessed via: > function get_string:string (str) > %{ > char astr[32]; > strcpy (astr,(char*)STAP_ARG_str); > STAP_RETURN (astr); > %} > > probe process("./tstclass.x").mark("test_probe_4") > { > printf("%s aa=%#lx string1=%s\n",pp(),@cast($arg1,"struct A")->aa, > get_string(@cast($arg1,"struct A")->string1->_M_dataplus->_M_p)) > } The @cast interprets arg1 as a struct A so the members can be accessed. The probes are translated to C so it uses internal knowledge to get at string1. (Is there an easier way to do this?) So that yields: % stap --dyninst -g --disable-cache tstclass.stp -c ./tstclass.x process("/this/dir/tstclass.x").statement(0x401283) aa=0xa string1=abc 10 20 abc xyz