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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m trying to implement a 10-bit relocation that does not start at the beginning of a byte-boundary and I’m not entirely sure I understand the use by some targets of MCFixup.Offset and MCFixupKindInfo.TargetOffset.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">LLVM’s documentation states that:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">MCFixup.Offset –“/// The byte index of start of the relocation inside the encoded instruction.”<o:p></o:p></p>
<p class="MsoNormal">MCFixupKindInfo.TargetOffset – “/// The bit offset to write the relocation into.”<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So if the relocation starts at bit 20 (assuming that the leftmost bit is bit number 31) I’d say that MCFixup.Offset = 1 and MCFixupKindInfo.TargetOffset = 3<o:p></o:p></p>
<p class="MsoNormal">and this is somehow confirmed by the code in MCAsmStreamer::AddEncodingComment. All the relocation bits are correctly identified if I emit the encoding of an instruction.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The other use of MCFixup.Offset is in MCELFStreamer::EmitInstToData and it looks like it uses MCFixup.Offset to calculate r_offset (Elf32) which is not what I was expecting because I get a slightly skewed offset (off by MCFixup.Offset).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I can obviously create the relocation with MCFixup.Offset to be 0 (which most of the targets do) but the code in MCAsmStreamer::AddEncodingComment will not work as expected (identification of relocation bits will be wrong) and will assert
in debug builds if the relocation does not start at the beginning of a byte-boundary (and mine doesn’t). I can set the size of the relocation to be the entire size of an instruction like some targets do (e.g.: ARM) but that doesn’t seem to be an elegant solution.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Could someone clarify the use of MCFixup.Offset ? At the moment I see some targets (e.g.: X86 and ARM) not bothering to set it to the value it’s supposed to be (byte index of the start of the relocation) and I can only imagine it’s because
that information is being used by the ELF streamer class to set r_offset.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Regards,<o:p></o:p></p>
<p class="MsoNormal">Matheus<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-align:justify"><b><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">Matheus Almeida<o:p></o:p></span></b></p>
<p class="MsoNormal" style="text-align:justify"><span style="font-size:10.0pt;font-family:"Arial","sans-serif"">MIPS processor IP<o:p></o:p></span></p>
<p class="MsoNormal" style="text-align:justify"><a href="http://www.imgtec.com/"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:blue">www.imgtec.com</span></a><span style="font-size:10.0pt;font-family:"Arial","sans-serif""><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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