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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Probably my misunderstanding of how the __asm__ extension should work then. I’ve been thinking that<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void g() __asm__(“real_g”) should behave the same as<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void real_g();<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">but thinking in terms of source-level names and assembly-level names makes sense to me. Thanks!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> metafoo@gmail.com [mailto:metafoo@gmail.com]
<b>On Behalf Of </b>Richard Smith<br>
<b>Sent:</b> Friday, December 11, 2015 12:57 PM<br>
<b>To:</b> Gao, Yunzhong<br>
<b>Cc:</b> Nick Lewycky; Clang Commits<br>
<b>Subject:</b> Re: PATCH: error on code that redeclares with an __asm__ label after the first ODR use<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Fri, Dec 11, 2015 at 12:43 PM, Gao, Yunzhong via cfe-commits <<a href="mailto:cfe-commits@lists.llvm.org" target="_blank">cfe-commits@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">gcc 4.8.2 accepts the following case silently without error or warning:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> void f();</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> void g() __asm__(“real_g”);</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> void f() { g(); } // gcc emits a call to real_g() here</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> void real_g() __asm__(“gold”);</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void real_g() { } // gcc generates a body for gold() here</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">gcc 4.8.2 generates a warning for the following test case:</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void g() __asm__(“func1”);</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void g() __asm__(“func2”); // gcc generates a warning and ignores this asm label</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void g() { }</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Comparing to gcc behavior, I think it is better to emit error in both cases.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Why? I don't see anything wrong with the first example. We have a function whose source-level name is "g()" and whose asm name is "real_g", and we have a function whose source-level name is "real_g()" and whose asm name is "gold". What's
wrong with that?<span style="color:#1F497D"><o:p></o:p></span></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Looks good to me. Thanks!</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">- Gao</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Nick Lewycky [mailto:<a href="mailto:nlewycky@google.com" target="_blank">nlewycky@google.com</a>]
<br>
<b>Sent:</b> Friday, December 11, 2015 12:44 AM<br>
<b>To:</b> Gao, Yunzhong<br>
<b>Cc:</b> Clang Commits<br>
<b>Subject:</b> Re: PATCH: error on code that redeclares with an __asm__ label after the first ODR use</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">On 10 December 2015 at 17:42, Gao, Yunzhong <<a href="mailto:yunzhong_gao@playstation.sony.com" target="_blank">yunzhong_gao@playstation.sony.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Out of curiosity, is the following test case possible too?</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void f();</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void g() __asm__(“real_g”); // rename g into real_g.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void f() {</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> g(); // this would actually be calling real_g()</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">}</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">void real_g() __asm__("gold"); // re-declaring real_g() into gold <-- should this be an error too?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I can't see any reason why not. Both clang and gcc will emit "real_g" here instead of "gold", but changing the asm label in a program is highly dubious. I added an error for this
too.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thanks!<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cfe-commits [mailto:<a href="mailto:cfe-commits-bounces@lists.llvm.org" target="_blank">cfe-commits-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>Nick Lewycky via cfe-commits<br>
<b>Sent:</b> Thursday, December 10, 2015 3:15 PM<br>
<b>To:</b> Clang Commits<br>
<b>Subject:</b> PATCH: error on code that redeclares with an __asm__ label after the first ODR use</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">PR22830 shows a case where some code was adding an __asm__ label after the first use of a function. GCC and Clang diverged on this code, GCC emitting the name in the last __asm__
label for all uses while clang would switch in the middle of the TU as the redeclaration was parsed. The attached patch detects this case and issues an error on such a redeclaration. If this breaks real code, we can turn it down to a warning.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Please review!<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Nick<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
_______________________________________________<br>
cfe-commits mailing list<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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