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<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">I’m looking for some guidance in adding/using the AVR LLVM backend with Clang. I don’t know if this is more appropriate for the llvm-dev list, so feel free to point me that
way if this has nothing to do with Clang. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">My understanding is that the latest LLVM trunk supports the AVR backend, so I checked out the source and tried building it. I stumbled across a few posts online mentioning
that the list of LLVM targets is specified in the top-level CMakeLists file. AVR isn’t in the list on the trunk, so I added it and ran CMake with -DLLVM_TARGETS_TO_BUILD=AVR. This works and prints out ‘-- Targetting AVR’, so it certainly
<i>looks </i>like this is working. During compilation, I also seem a promising list of targets being built — AVRCommonTableGen, LLVMAVRCodeGen, etc.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">Is this all it takes to build in the backend? I’ve tried using it but haven’t had any luck. I’ll give a few examples.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">> clang --target=avr main.c -o main.o<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">error: unable to create target: 'No available targets are compatible with this triple.'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">1 error generated.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">> clang --target=avx main.c -o main.o<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">error: unknown target triple 'avx', please use -triple or -arch<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">My dummy target generates a different error than when I pass in avr, so again, it looks like LLVM/Clang has
<i>some </i>understanding that AVR targets are supported.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">I understand that before being integrated into the trunk, the backend was implemented as the ‘avr-llvm’ project. Looking at its wiki, the guide says to pass the ‘-mmcu’ flag
to Clang. This doesn’t seem to work either<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">> clang --target=avr main.c -o main.o -mmcu=atmega1284p<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">clang-5.0: error: unknown argument: '-mmcu=atmega1284p'<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">Also, this may be irrelevant, but the string ‘mmcu’ doesn’t appear anywhere in the Targets/AVR source directory. This makes me think that the calling convention may have changed.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">Finally, my output from ‘llc --version’ does not show ‘avr’ as a registered target. This seems like it is very important, but again, I don’t really know.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">Any help would be appreciated. Does it look like I configured the build properly with CMake? Am I passing the wrong arguments to Clang? Is the AVR backend not fully integrated?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111">Thanks!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Segoe UI","sans-serif";color:#111111"><o:p></o:p></span></p>
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