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Re: Help text for ld magic number options
- From: Stephen Casner <casner at acm dot org>
- To: Andreas Schwab <schwab at suse dot de>
- Cc: binutils at sourceware dot org
- Date: Mon, 24 Feb 2020 13:26:32 -0800 (PST)
- Subject: Re: Help text for ld magic number options
- References: <alpine.OSX.2.21.9999.2002221231070.32566@auge-10.local> <mvm7e0cz6yx.fsf@suse.de>
On Mon, 24 Feb 2020, Andreas Schwab wrote:
> On Feb 22 2020, Stephen Casner wrote:
>
> > I propose that the help text be changed as follows:
> >
> > -n, --nmagic Make text readonly, page align data, no demand paging
> > -N, --omagic Do not make text readonly, do not page align data
> > --no-omagic Make text readonly, page align data, do demand paging
> >
> > Is that acceptable? This would have implications for the ld
> > documentation as well.
>
> I think there is some confusion about what "alignment" means in this
> context. Here is what the manpage says:
>
> OMAGIC The text and data segments immediately follow the
> header and are contiguous. The kernel loads both text
> and data segments into writable memory.
>
> NMAGIC As with OMAGIC, text and data segments immediately fol-
> low the header and are contiguous. However, the kernel
> loads the text into read-only memory and loads the data
> into writable memory at the next page boundary after
> the text.
>
> ZMAGIC The kernel loads individual pages on demand from the
> binary. The header, text segment and data segment are
> all padded by the link editor to a multiple of the page
> size. Pages that the kernel loads from the text seg-
> ment are read-only, while pages from the data segment
> are writable.
>
> The alignment appears to refer to the padding added by the link editor
> in the ZMAGIC format.
Thanks for that clarification. I think "padding" would be the more
operative word than "alignment" here, noting that the latter word does
not appear in the cited paragraphs.
How about:
-n, --nmagic Text in readonly pages, not padded for demand paging
-N, --omagic Do not make text readonly, do not page align data
--no-omagic Make text readonly, align and pad for demand paging
In both my original proposal and this one, the --no-omagic description
is inaccurate for the pdp11-aout format because padding to page
boundaries is never done, but there isn't a way to omit the common
options for some emulations.
-- Steve