Re: [PATCH RFC 19/67] MIPS: asm: atomic: Update asm and ISA constrains for MIPS R6 support

On Fri, 19 Dec 2014, Markos Chandras wrote:

quoted

Obviously to use anything other than the 'm' constraint you are going
to need to know when any given constraint was added to GCC.
'ZC' was only added to GCC in March 2013 r196828 which I believe it is a
GCC 4.9 feature so you will have to use it conditionally if you use it at
all.

is this something desirable? check the gcc version, initialize a macro
and then use that macro as a constrain? i haven't thought this through,
but it could be a bit messy.

 There is prior art for this, see arch/mips/include/asm/compiler.h and 
then grep the tree for uses.

  Maciej