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</o:shapelayout></xml><![endif]--></head><body lang=EN-IE link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>My own preference is for a warning, that way the issue is visible and the programmer can choose to ignore it, disable it or make it an error as preferred.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>I tried it with embedded NUL characters, and this turned out not to be a good idea. The example:<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>__attribute__((section("grok\nfubar\0poisoned\tsnafu")))<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>int foo() { return 42; }<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>with clang v3.8.0 for X86 ‘</span><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>clang -Wall -S section.c</span><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>’ I get the following output and no warnings:<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .text<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .def foo;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .scl 2;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .type 32;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .endef<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .section grok<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>fubar,"xr"<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .globl foo<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .align 16, 0x90<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>foo: # @foo<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>.Ltmp0:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>.seh_proc foo<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'># BB#0: # %entry<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>.Ltmp1:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .seh_endprologue<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> movl $42, %eax<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> retq<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .seh_handlerdata<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .section grok<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>fubar,"xr"<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>.Ltmp2:<o:p></o:p></span></p><p class=MsoNormal style='margin-left:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'> .seh_endproc</span><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>Since we do not have an integrated assembler, we have to go through the emit-assembly and separate invocation of the assembler, and such constructs fail at the next level.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>I don’t know, perhaps when the compiler is writing object code directly it can somehow make the whole string meaningful as a section name, though I’m not sure how I could write an LD script for such sections.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>I don’t advocate the programmer doing this kind of trick to force assembly code into the emitted assembly code; it seems very dangerous. The ‘</span><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>__attribute__((naked))</span><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>’ was changed a few versions ago so that a function defined with this attribute could not contain C source code. I haven’t experimented with it since then.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'> MartinO <o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#1F497D;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org] <b>On Behalf Of </b>mats petersson via llvm-dev<br><b>Sent:</b> 05 October 2016 21:48<br><b>To:</b> Joerg Sonnenberger <joerg@bec.de>; llvm-dev <llvm-dev@lists.llvm.org><br><b>Subject:</b> Re: [llvm-dev] Using '__attribute__((section("name")))' for inline assembly injection<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On 5 October 2016 at 21:39, Joerg Sonnenberger via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal>On Wed, Oct 05, 2016 at 12:44:29PM -0500, Hal Finkel via llvm-dev wrote:<br>> Would it be useful for Clang to warn about section names with unusual characters?<br><br>I don't think it is common enough and you can always check the output<br>easily with readelf/objdump.<o:p></o:p></p></blockquote><div><p class=MsoNormal><br>I would think that it's very uncommon, however, it is also terribly difficult to detect, and I'd argue that it's unlikely that someone actually wishes to have newlines or other "non-printable"/"control" characters in the section name. And if it's a warning that is enabled by default but possible to turn off with "-wno-weird-sectionname", I'd say it would be little harm - and not a huge maintenance burden. <br><br>Knowing to check that the section names contain weirdness or otherwise debug "why the heck doesn't this code work in Clang, when it compiels without warning, and is fine when compiled in gcc or whatever" is really not at all easy.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I do realise that "every warning and such is a maintenance burden", but although I have not encountered this problem, I'd definitely prefer a warning than having to figure what went wrong...<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>--<o:p></o:p></p></div><div><p class=MsoNormal>Mats<o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal><br>Joerg<o:p></o:p></p><div><div><p class=MsoNormal>_______________________________________________<br>LLVM Developers mailing list<br><a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br><a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p></div></div></blockquote></div><p class=MsoNormal><o:p> </o:p></p></div></div></div></body></html>