Lars Brinkhoff <lars.spam@nocrew.org> writes:
> You can try passing "-mgfloat" go gcc

Might as well list all the PDP-10-specific compiler switches:

-gtops20
    Generate TOPS-20 format debug info.  Temporary hack until the
    debug info format has been decided.  NetBSD will use Dwarf 2, I
    guess.

-mconvert-voidp
-mno-convert-voidp
    Do or don't convert to/from void *.  XKL-specific hack; don't use
    it.

-mac0
    Output AC0 even if it's not used by the instruction.  E.g.
    "skipg 0,foo".  This is only a matter of taste.

-mindent-skipped
    Indent skipped instructions.  E.g.
        skipg 1,foo
         jrst bar
    This is only a matter of taste.

-mupper
    Upper-case opcodes.  E.g. JFCL instead of jfcl.  This is only a
    matter of taste.

-mtab

    Tab between opcode and operands.  One space character is the
    default.  This is only a matter of taste.

-mno-string
-mstring
    Don't or do use string intstructions.  Currently useless, because
    string instructions are never used.

-mdfloat
-mgfloat
    Use double- or giant-format for C type "double".

-munextended
-mextended
    Don't or do use extended addressing.

-mchar-bytesize=<n>
    What byte size to use for the char type.  6, 7, 8, and 9 are valid
    values.  9 is the default.

-mstring-bytesize=<n>
    What byte size to use for string literals.  Same range and default
    as above.

-mcall-clobbered=<n>
    Number of registers that are call clobbered.  Default is 8, which
    means that AC0-AC7 are call clobbered.

-mreturn-regs=<n>
    Number of registers used to return a value.  Default is 7: AC1-AC7.

-mregparm=<n>
    Number of registers used to pass arguments.  Default is 7: AC1-AC7.

-mmodel=<string>
    Specify program model:
        small           Everything in one section.
        smallish        Most things in one sections (default).
        large           Most things in multiple sections.

-mpsect=<string>
    Specify the name of the PSECT to put code in.  Default is ".text".
    Only relevant in TOPS-20, I guess.

-mtune=<cpu>
    Select which processor to tune code generation for.  Default is
    xkl1, but no particular tuning is done yet.

-march=<cpu>
    Select the processor which instruction set to use.  Default is
    xkl1, which has the same instruction set as the KL10.  Possible
    processors are:
        166             Type 166, used in PDP-6.
        ka10            KA10, used in PDP-10 and early DECsystem-10.
        ki10            KI10, used in DECsystem-10[67]x.
        kl10            KL10, used in DEC-10[89]x and DEC-20[456]x.
        ks10            KS10, used in DECSYSTEM-2020.
        xkl1            XKL-1, used in TOAD-1.
        xkl2            XKL-2, future XKL processor?

-mcpu=<cpu>
    Equivalent to "-mtune=<cpu> -march=<cpu>".