Comment 10 for bug 488354
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0e1f616
(Get the code!)
You can (and should) use BLX all the time in this case, but it won't then work on ARMv4. The JIT doesn't work on ARMv4 anyway, and I don't think we care about such old machines.
Having said that, some distributions might care about ARMv4, and they might want support, even if it's slow. (Don't ask me why!) A solution here would be to use the old-style "MOV pc, ip" on ARMv4 (using a compile-time switch of some kind) and BLX everywhere else. We would also have to disable the JIT for ARMv4, but ARMv4 distributions must do that anyway because the JIT hasn't had ARMv4 support for a long time.
NOTE: Using "MOV pc, ip" will break the return stack prediction on newer cores, so even if you don't want to interwork, use BLX <reg>. The performance difference should be significant.