• RegisterConventions

PA-RISC Linux Register Conventions

A file in the kernel tree describes the registers specified by the ABI.

A stack frame for a function in the 32-bit runtime looks like this:

   Offset
        [ Variable args ]
   SP = (4*(n+9))       arg word N
   ...
   SP-52                arg word 4
        [ Fixed args ]
   SP-48                arg word 3
   SP-44                arg word 2
   SP-40                arg word 1
   SP-36                arg word 0
        [ Frame marker ]
   ...
   SP-20                RP
   SP-4                 previous SP

• First 4 non-FP 32-bit args are passed in gr26, gr25, gr24 and gr23
• First 2 non-FP 64-bit args are passed in register pairs, starting on an even numbered register (i.e. r26/r25 and r24+r23)
• First 4 FP 32-bit arguments are passed in fr4L, fr5L, fr6L and fr7L
• First 2 FP 64-bit arguments are passed in fr5 and fr7
• The rest are passed on the stack starting at SP-52, but 64-bit arguments need to be aligned to an 8-byte boundary