[LLVMdev] ARM thumb-2 instruction used for non-thumb2 CPUs

[Jim Grosbach]

On Jun 22, 2011, at 4:02 PM, Damjan Marion wrote:
>> 
>> To get -integrated-as working so that we don't need to go through the assembler at all should be mostly a matter of bug fixing, modulo inline assembly support. For non-trivial inline assembly, and to get a system assembler replacement based on the MC assembler, it'll be a bigger task. The ARM asm parser is currently in need of some tender loving care. That's coming soon, but it's a non-trivial task.
>> 
>> For -integrated-as, I would suggest giving it a try. I'm not completely sure how complete the support is for ELF, but I think it's in somewhat OK shape, at least. Worth trying. That would neatly avoid the problem if it works. If it doesn't, we should fix the bugs so it does. ;)
> 
> I tried with FreeBSD kernel. Outcome is 2 different crashes. Output is here:
> 
> http://web.me.com/dmarion/FreeBSD/integrated-as_crash.txt
> 
> I can provide more details if needed.


Thanks, Damjan. That's good information.

Crash #1 is an assembly source file. It's running into something it doesn't understand on the line indicated. The assertion failure is a secondary problem, and definitely shouldn't happen. As mentioned, though, the asm parser isn't ready for prime time yet, so I suspect this may be just the tip of the iceberg as far as the problems that (and similar) files would encounter.

Crash #2 is a C file, but is also asserting in the assembly parser, which indicates that there's inline assembly in the file somewhere that the parser doesn't know how to handle yet.

Some Makefile magic should be able to take care of issues of the sort encountered in #1 (don't pass -integrated-as when compiling .S files).

Inline assembly is a bit trickier. Temporarily, if those files compile/assemble OK with the system assembler (i.e., don't have the rrx instruction mnemonic in them), we could work around by not using -integrated-as for them. That's pretty fugly, though, and would just be a quick workaround to allow you to keep making progress while the real issues get fixed.

How much inline asm is there in that file that's causing issues? if it's not too much, it might not be too bad to get at least that much of the asm parsing working. That would be general goodness and would help move you forward.

-Jim