PA-RISC Linux Register ConventionsΒΆ

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