[LLVMdev] STM8 backend for Clang

[Andreas Färber]

Hi there,

Inspired by the recent FOSDEM keynote, I've tried to write an LLVM  
backend for the STM8 microcontroller platform. The STM8S-Discovery  
evaluation board [1] has been handed out for free or is sold dirt- 
cheap, but there is no Open Source cross-compiler for it. The  
available ST assembler, linker and USB flash programmer are closed- 
source Windows binaries. And the compiler vendor I contacted for an  
evaluation license has failed to react at all. So, I was hoping to  
piece together an STM8 backend for LLVM, for Clang to be able to  
compile C code into STM8 assembler code that - as a first step - I  
might be able to use with the ST assembler on some Windows box and  
transfer it to the board there.

Here's what I've put together so far:
http://repo.or.cz/w/llvm/stm8.git
http://repo.or.cz/w/clang/stm8.git

The first issue I stumbled upon was that the Program Counter register  
is 24 bits. It seems that despite having been discussed in the past  
[2], value type i24 was never added. On my branch I did so and, due to  
ordering assumptions, had to adjust ~30 type enum values in both files  
[3]. Would such a binary-incompatible change be acceptable for trunk  
at all?
Further, as pointer width I chose 16 bits since there currently seems  
to be no way to distinguish between near and far pointers?

Anyway, I've put together enough skeleton code to successfully  
compile, but on Mac OS X v10.5 ppc host this is what I get:

$ Debug+Asserts/bin/clang -ccc-host-triple stm8-unknown-elf ../hello.c  
-S -o ../hello.s
0  clang             0x0168c4f0  
llvm::SearchForAddressOfSpecialSymbol(char const*) + 448
1  clang             0x0168cc8c llvm::sys::RunInterruptHandlers() + 456
2  libSystem.B.dylib 0x9422d9fc _sigtramp + 68
3  clang             0x0159692c std::_Rb_tree<void const*,  
std::pair<void const* const, llvm::Pass*>,  
std::_Select1st<std::pair<void const* const, llvm::Pass*> >,  
std::less<void const*>, std::allocator<std::pair<void const* const,  
llvm::Pass*> > >::_M_insert(std::_Rb_tree_node_base*,  
std::_Rb_tree_node_base*, std::pair<void const* const, llvm::Pass*>  
const&) + 132
4  clang             0x0f1c1cc0 std::_Rb_tree<void const*,  
std::pair<void const* const, llvm::Pass*>,  
std::_Select1st<std::pair<void const* const, llvm::Pass*> >,  
std::less<void const*>, std::allocator<std::pair<void const* const,  
llvm::Pass*> > >::_M_insert(std::_Rb_tree_node_base*,  
std::_Rb_tree_node_base*, std::pair<void const* const, llvm::Pass*>  
const&) + 230863896
Stack dump:
0.	Program arguments: /Users/andreas/STM8S-Discovery/llvm-stm8/Debug 
+Asserts/bin/clang -cc1 -triple stm8-unknown-elf -S -disable-free - 
main-file-name hello.c -mrelocation-model static -mdisable-fp-elim - 
mconstructor-aliases -target-linker-version 85.2.1 -momit-leaf-frame- 
pointer -resource-dir /Users/andreas/STM8S-Discovery/llvm-stm8/Debug 
+Asserts/bin/../lib/clang/2.9 -ferror-limit 19 -fmessage-length 274 - 
fgnu-runtime -fdiagnostics-show-option -fcolor-diagnostics -o ../ 
hello.s -x c ../hello.c
1.	<eof> parser at end of file
clang: error: unable to execute command: Bus error
clang: error: clang frontend command failed due to signal 1 (use -v to  
see invocation)

Same for stm8-unknown-none. Configured with --enable- 
targets=host,stm8. (It still works for the default Darwin/ppc target.)

I'm fairly sure there's things I haven't implemented yet but I'm  
missing an assertion or error message as hint where to continue.  
Neither printf()s nor gdb breakpoints in the above  
llvm::SearchForAddressOfSpecialSymbol() are reached.

Any hint what's going wrong or how to debug? Thanks!

Regards,

Andreas

[1] http://www.st.com/stm8s-discovery
[2] http://lists.cs.uiuc.edu/pipermail/llvmdev/2008-November/018663.html
[3] http://repo.or.cz/w/llvm/stm8.git/commitdiff/79de4e74e2bc33894cfef4487be06e4005a1a7a0