• Herbert Valerio Riedel's avatar
    Add NCG support for AIX/ppc32 · df26b955
    Herbert Valerio Riedel authored
    This extends the previous work to revive the unregisterised GHC build
    for AIX/ppc32. Strictly speaking, AIX runs on POWER4 (and later)
    hardware, but the PPC32 instructions implemented in the PPC NCG
    represent a compatible subset of the POWER4 ISA.
    
    IBM AIX follows the PowerOpen ABI (and shares many similiarites with the
    Linux PPC64 ELF V1 NCG backend) but uses the rather limited XCOFF
    format (compared to ELF).
    
    This doesn't support dynamic libraries yet.
    
    A major limiting factor is that the AIX assembler does not support the
    `@ha`/`@l` relocation types nor the ha16()/lo16() functions Darwin's
    assembler supports. Therefore we need to avoid emitting those. In case
    of numeric literals we simply compute the functions ourselves, while for
    labels we have to use local TOCs and hope everything fits into a 16bit
    offset (for ppc32 this gives us at most 16384 entries per TOC section,
    which is enough to compile GHC).
    
    Another issue is that XCOFF doesn't seem to have a relocation type for
    label-differences, and therefore the label-differences placed into
    tables-next-to-code can't be relocated, but the linker may rearrange
    different sections, so we need to place all read-only sections into the
    same `.text[PR]` section to workaround this.
    
    Finally, the PowerOpen ABI distinguishes between function-descriptors
    and actualy entry-point addresses. For AIX we need to be specific when
    emitting assembler code whether we want the address of the function
    descriptor `printf`) or for the entry-point (`.printf`). So we let the
    asm pretty-printer prefix a dot to all emitted subroutine
    calls (i.e. `BL`) on AIX only. For now, STG routines' entry-point labels
    are not prefixed by a label and don't have any associated
    function-descriptor.
    
    Reviewers: austin, trommler, erikd, bgamari
    
    Reviewed By: trommler, erikd, bgamari
    
    Differential Revision: https://phabricator.haskell.org/D2019
    df26b955
PprBase.hs 4.3 KB