>>>>> der Mouse writes:

der> Which %g registers can I count on not changing behind my back?

It's defined by the Sparc ABI. There is a comment in the GCC sources
describing it (src/gnu/dist/toolchain/gcc/config/sparc/sparc.h),
appended below.

However, despite that comment, I used %g5 and %g7 for a very long time
when developing a compiler for my PhD thesis, and I never saw any
problems related to that. This was pre-v9, on both NetBSD and Solaris.

YMMV... ;-)

Kind regards,

        -- Urban

/* 1 for registers that have pervasive standard uses
   and are not available for the register allocator.

   On non-v9 systems:
   g1 is free to use as temporary.
   g2-g4 are reserved for applications.  Gcc normally uses them as
   temporaries, but this can be disabled via the -mno-app-regs option.
   g5 through g7 are reserved for the operating system.

   On v9 systems:
   g1,g5 are free to use as temporaries, and are free to use between calls
   if the call is to an external function via the PLT.
   g4 is free to use as a temporary in the non-embedded case.
   g4 is reserved in the embedded case.
   g2-g3 are reserved for applications.  Gcc normally uses them as
   temporaries, but this can be disabled via the -mno-app-regs option.
   g6-g7 are reserved for the operating system (or application in
   embedded case).
   ??? Register 1 is used as a temporary by the 64 bit sethi pattern, so must
   currently be a fixed register until this pattern is rewritten.
   Register 1 is also used when restoring call-preserved registers in large
   stack frames.

   Registers fixed in arch32 and not arch64 (or vice-versa) are marked in
   CONDITIONAL_REGISTER_USAGE in order to properly handle -ffixed-.
*/