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Date: Fri, 31 Jan 2020 22:11:21 +0300
From: Андрей Аладьев <aladjev.andrew@...il.com>
To: musl@...ts.openwall.com
Subject: Re: Static linking is broken after creation of DT_TEXTREL segment
Now everything is clear, thank you. Have a good weekend =)
пт, 31 янв. 2020 г. в 21:01, Rich Felker <dalias@...c.org>:
> On Fri, Jan 31, 2020 at 08:51:05PM +0300, Андрей Аладьев wrote:
> > > Moreover, adding such a thing is not desirable because it adds a
> > linear-search of an array of load segments to each relocation
> >
> > I think it is possible to make this search O(log n).
>
> This would help if n were large, but in practice it's very small (2-3
> or maybe 4) and the cost is just the code path overhead, which gets
> worse if you do that, not the largeness of n.
>
> > for (j=0; v-p->loadmap->segs[j].p_vaddr >= p->loadmap->segs[j].p_memsz;
> > j++);
> >
> > This code takes first segment that can handle address. It looks possible
> to
> > create modified list of virtual segments, that won't overlap and make a
> > binary search.
>
> They're non-overlapping anyway but not necessarily sorted, and can't
> be simultaneously sorted by addr and p_vaddr since the orders will
> differ.
>
> > > This is not a reasonable tradeoff and it's why I proposed the "hull"
> > approach
> >
> > It may not be safe from maintainability perspective. Library will be
> > changed, everybody will forget what part of code was protected by
> external
> > validation and it will provide unexpected behaviour. Please consider
> double
> > validation approach:
>
> You're really not making sense here. What does "protected by external
> validation" mean? There is presently nothing being "protected" here;
> the discussion is just about more informative errors. If this is used
> as a boundary for some sort of safety at some point in the future (as
> mentioned before, the benefit of this is probably limited to ldd and
> thus not very useful) then it will be done according to constraints
> needed to achieve that.
>
> > external validation in production and debug only mode
> > with loadmap like validation.
>
> We do not have separate "production" and "debug" modes. This kind of
> thing (combinatoric build-time options) is what lacks maintainability.
>
> Rich
>
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