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<p class="MsoNormal">>Downstream object consumers that check to verify that a DWARF attr is appropriate for a given DWARF tag will appropriately flag an error.<span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Such a downstream consumer is behaving inappropriately. DWARF is a "permissive" standard, and the use of an attribute in a novel situation is explicitly permitted (see section 1.3 of DWARF v4). Consumers are
expected to ignore tags and attributes that they do not recognize.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">The sort of verification you describe might be appropriate for a producer that supported a "strict DWARF" mode, and used only those tags, attributes, and combinations that are explicitly described in a given
DWARF version. LLVM does not have such a mode, and the DWARF specification does not require it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="color:#1F497D"><o:p> </o:p></span></a></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""> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>Snider, Todd via llvm-dev<br>
<b>Sent:</b> Tuesday, July 30, 2019 12:59 PM<br>
<b>To:</b> llvm-dev<br>
<b>Subject:</b> Re: [llvm-dev] Invalid DW_AT_calling_convention generated for a DW_TAG_class_type<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#1F497D">I see now that this is a DWARF 5 addition. It is still invalid for DWARF 4 or earlier.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="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""> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>Snider, Todd via llvm-dev<br>
<b>Sent:</b> Tuesday, July 30, 2019 11:54 AM<br>
<b>To:</b> llvm-dev<br>
<b>Subject:</b> [EXTERNAL] [llvm-dev] Invalid DW_AT_calling_convention generated for a DW_TAG_class_type<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp, the compiler can emit a DW_AT_calling_convention attribute with a DW_TAG_class_type (and it looks like a DW_TAG_variant_part, DW_TAG_structure_type or DW_TAG_union_type as well), but the DWARF
4 specification says that DW_AT_calling_convention is not a valid attribute for any of those three DWARF tags.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Downstream object consumers that check to verify that a DWARF attr is appropriate for a given DWARF tag will appropriately flag an error.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I conjecture that this part of the DwarfUnit::constructTypeDIe() function (circa line 958 in DwarfUnit.cpp) should be guarded with a target- or vendor-specific conditional if it is needed for a particular purpose. Otherwise, I propose that
it be removed since it breaks compliance with the DWARF specification.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">~ Todd Snider<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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