Re: [PATCH 2/2 v5] gold: enable new dtags by default

[Mike Frysinger <vapier at gentoo dot org>]

On Wednesday 20 February 2013 12:16:51 H.J. Lu wrote:
> On Tue, Feb 19, 2013 at 10:15 PM, Mike Frysinger <vapier@gentoo.org> wrote:
> > On Tuesday 05 February 2013 00:43:04 Ian Lance Taylor wrote:
> >> On Mon, Feb 4, 2013 at 5:44 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> >> > This caused:
> >> > 
> >> > http://www.sourceware.org/bugzilla/show_bug.cgi?id=15098
> >> > 
> >> > I changed BFD linker not set new dtags with -rpath.
> >> 
> >> I don't see why that is the right fix.  Since DT_RPATH/DT_RUNPATH are
> >> only ever set by the linker's -rpath option, it seems like the right
> >> fix is to always use DT_RPATH and never use DT_RUNPATH.
> >> 
> >> Of course, since the only thing --new-dtags does in gold is select
> >> DT_RUNPATH rather than DT_RPATH, this makes new--dtags completely
> >> useless in gold.
> >> 
> >> It seems that we have made sensible-seeming decisions to wind up in an
> >> absurd place.  It seems that we should now make --new-dtags a no-op
> >> and drop all support for generating DT_RUNPATH.  Which makes me wonder
> >> why DT_RUNPATH was invented in the first place.
> > 
> > sorry, but my main comp hd died, so i've been offline for a while.  it
> > seems that the current status is that the linker no longer defaults to
> > --enable-new- dtags, but bfd still only specifies DT_RUNPATH if the flag
> > is enabled (rather than using both).  is that correct ?
> > 
> > DT_RUNPATH is preferable to DT_RPATH because the latter is searched
> > *before* LD_LIBRARY_PATH which is bad.  most of the use cases i've seen
> > with rpath fall
> > 
> > into two categories:
> >  - people want to generate libraries with a custom path to loadable
> >  plugins --
> > 
> > DT_RUNPATH works great
> > 
> >  - people want their application to search a local path for all of its
> >  libs --
> > 
> > DT_RPATH works here w/$ORIGIN
> > 
> >  - people want to install their shared libs into a non-searchable path
> >  and
> > 
> > have their application use it -- DT_RUNPATH works here
> > 
> > i've seen build cases where DT_RPATH actively causes problems when there
> > is a version already installed.  they compile their local binary and its
> > shared libs, then attempt to use LD_LIBRARY_PATH to force the binary to
> > use the local libs.  unfortunately, the DT_RPATH kicks in and loads
> > everything from / instead and it falls down.
> > 
> > considering Gentoo has been defaulting to --enable-new-dtags since at
> > least 2004 and i have yet to see a bug report related to it, i wonder
> > what actually broke that caused you to notice this ?  and if it's a
> > minor case, is a better answer to tell people to use --disable-new-dtags
> > if they really don't want the new DT_RUNPATH behavior ?  seems like the
> > DT_RPATH behavior is the exception rather than the rule ... the only
> > thing it has going for it is historical precedence.
> > 
> > similarly, i don't think it generally makes sense for libraries to
> > utilize DT_RPATH.  dare i suggest that a middle ground might be to
> > default to DT_RUNPATH when -shared is in use, and DT_RPATH otherwise ?
> 
> Since DT_RPATH != DT_RUNPATH. we need a new option to
> specify DT_RUNPATH.

i'm aware "DT_RPATH != DT_RUNPATH" is a true statement.  however, my point 
still stands that for the majority of cases, people want runpath tags to 
specify custom paths for loading libraries and in that regard, DT_RUNPATH is 
the same as DT_RPATH.  imo, the example you posted is the exception rather 
than the rule when it comes to expected behavior and already works w/the 
patches i posted -- if you want that behavior, use -rpath --disable-new-dtags.  
hence the idea is to improve the default rather than requiring everyone to 
change flags.
-mike

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