Hello,
Paul Burton wrote:
> The GCC_OFF_SMALL_ASM macro defines the constraint to use for
> instructions needing "small offsets", typically the LL or SC
> instructions. Historically these had 16 bit offsets, but microMIPS &
> MIPS32/MIPS64r6 onwards reduced the width of the offset field.
>
> GCC 4.9 & higher supports a ZC constraint which matches the offset
> requirements of the LL & SC instructions. Where supported we can use
> the ZC constraint regardless of ISA, and it will handle the requirements
> of the ISA correctly. As such we require 3 cases:
>
> - GCC 4.9 & higher can use ZC.
>
> - GCC older than 4.9 must use the older R constraint, which does not
> take into account microMIPS or MIPSr6.
>
> - microMIPS builds therefore require GCC 4.9 or higher. MIPSr6 support
> was only introduced in newer compilers anyway so it can be ignored
> here.
>
> The current code complicates this a little by specifically having MIPSr6
> bypass the GCC version check, and using the R constraint for pre-MIPSr6
> builds even if the compiler supports ZC which would be equivalent.
>
> Simplify this such that the code straightforwardly implements the 3
> cases outlined above.
>
> For non-GCC compilers we presume that ZC is safe to use. In practice the
> only non-GCC compiler of interest is clang and it has supported the ZC
> constraint since version 3.7.0. It seems safe enough to presume that
> nobody will expect to built a working kernel using a clang version older
> than that, and if they do then they'll have bigger problems. As such we
> don't check the clang version number & just presume ZC is usable when
> the compiler is not GCC.
>
> Signed-off-by: Paul Burton <paul.burton@xxxxxxxx>
Applied to mips-next.
Thanks,
Paul
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