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avr-llvm / llvm

[MERGED UPSTREAM] AVR backend for the LLVM compiler library
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The 'architecture' field inside the ELF header is not being set #155

Closed seanmkauffman closed 9 years ago

seanmkauffman commented 9 years ago

When compile to an object file using llvm-mc with -triple=avr-none -mcpu=atmega2560 and then try to link with ld, I get an error that the architecture is incompatible.

$ ~/workspace/avr-work/bin/llvm-mc -triple=avr-none -mcpu=atmega2560 -filetype=obj fourierf.s -o fourierf.o
$ ~/workspace/avr-work/bin/llvm-mc -triple=avr-none -mcpu=atmega2560 -filetype=obj fftmisc.s -o fftmisc.o
$ avr-gcc -mmcu=atmega2560 -I. fftmisc.o fourierf.o test.o -o test.elf -Wl,-Map=main.map,--cref
/usr/libexec/gcc/avr/ld: avr architecture of input file `fftmisc.o' is incompatible with avr:6 output
/usr/libexec/gcc/avr/ld: avr architecture of input file `fourierf.o' is incompatible with avr:6 output
...

It looks like the object files are specifying the architecture without the version that ld is expecting. This appears to occur regardless of the contents of the source file, so long as I'm compiling with these flags.

I tried removing the -triple argument, but then it won't assemble properly. It's possible I'm not specifying the flags properly, but I couldn't figure out how to resolve this from digging around in the code.

dylanmckay commented 9 years ago

It's probably a bug in the subtarget feature descriptions. I'll investigate.

dylanmckay commented 9 years ago

The atmega2560 is apart of the avr6 architecture, and we make sure that we only emit instructions that this family supports.

What we aren't doing, however, is setting the architecture field inside the ELF header appropriately - we always set it to avr. The reason why AVR-GCC is failing to link the program is because it expects the architecture to be set to avr6 in the ELF header.