[Bug-gnupress] gcc.006.txt unanswered questions

[Paul A. Crable]

I had several questions imbeded in my changes for section 3.17.1 but
did not receive answers:

" -m68881
            Generate code for a ?????. The code will invoke 68881
instruction for floating point processing.  Unless the '--nfp' option
was specified when the compiler was configured, this option is on by
default and may be omitted."

??? The last two sentences don't make sense to me

 " -m68040
            Generate code for a 68040. If the compiler has been
configured for 68040based microcontrollers, this option is set by
default and may be omitted.  If the compiler has been configured for
other systems, then this option will force GCC to generate code for
the 68040.  This option inhibits the production of 68881/68882
instructions that have to be emulated by software on the 68040. Use
this option if your 68040 does not have code to emulate those
instructions."

??? The last two sentences don't make sense to me. I don't see how
instructions can be emulated in software on a hardware device. In my
experience, software is used to emulate features that are expected to
be provided by the hardware but are not in place; e.g., floating
point processing on an Intel 8086 with the 8087 is missing.

"-m68020-40
            Generate code for a 68040 but do not use the new
instructions..."

??? Is it going to be clear to the reader what the "new instructions"
are?

" -msoft-float
            Generate code containing calls to software for floating
point processing.  Be advised that supporting libraries are not
available for all m68k targets. Normally the facilities of the
machine's usual C compiler are used, but this can't be done directly
in crosscompilation. You must make your own arrangements to provide
suitable library functions for cross compilation. The embedded
targets `m68k-*-aout' and `m68k-*-coff' do provide software floating
point support."

??? The last three sentences don't make sense to me. If they are
clear to everyone else, then that's OK.

"-mpcrel
     Use the pcrelative addressing mode of the 68000 directly,
instead of using a global offset table. If -mpcrel is set, then -fpic
is set by default, allowing at most a 16bit offset for pcrelative
addressing. `-fPIC' is not presently supported with `-mpcrel', though
this could be supported for 68020 and higher processors.

??? It seems the last sentence contradicts the one before it.

    -mno-strict-align
    -mstrict-align
            Assume (?????) or do not assume (?????) that unaligned
memory references will be handled by the system.

??? Which selection is used for which function?