Re: SPARC Solaris global (g2-g4) register preservation question

"Norman Black" <stonybrk@ix.netcom.com> writes:


>I am porting our Modula-2 compiler (the others get a free ride) to
>SPARC Solaris from the Intel world. I wonder if anyone has information
>on the preservation of the application reserved global registers
>g2-g4.
>
>The ABI states preserved across procedure calls. Another document I
>saw said preserved across system calls.


GCC treats these registers as scratch registers (caller-save) by
default. So if you want to interoperate with code compiled with GCC,
you can't assume that they will be preserved across procedure calls.


The comments in the gcc source code (gcc/config/sparc/sparc.h) give
some additional information:


  | On non-v9 systems:
  ...
  | g2-g4 are reserved for applications. Gcc normally uses them as
  | temporaries, but this can be disabled via the -mno-app-regs option.
  ...
  | 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.
  ...


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