Posted on May 17, 2011 at 14:29It was my impression that ''clobbered'' is specifically for registers used explicitly in the ASM code - that's the primary reason for using symbolics, so the compiler can determine for itself which registers to use, because it selects them itself. And as you note, there does not appear to be a way to denote ''clobbered'' symbolics.
I suspect GCC warns, because it is not fully aware of the STREX and LDREX instruction formats.
That's just a guess, but I did an experiment. I replaced LDREXH with LDRH, replaced STREXH with STRH (removing the result register argument), and removed the ''result'' input/output specifier, and the CMP instruction which reads ''result''. That code produced no warnings, which implies to me that GCC understands the nature of LDRH and STRH operands, but not LDREXH and STREXH operands - otherwise it would have continued to warn about the ''temp_reg'' usage.
