Trouble doing bootstrap

[Ralf Wildenhues]

* Ian Lance Taylor wrote on Thu, Oct 14, 2010 at 08:43:51PM CEST:
> Ralf Wildenhues writes:
> > OK.  I won't argue my point further, but I am interested to learn why
> > shared libraries in nonstandard locations are seemingly frowned upon
> > here.  Is that due to fragility of the libtool approach of relinking,
> > or for relocatability issues of the installed program?
> 
> 1) We don't use libtool to build gcc.

I know.  That's easily "fixed" though.[1]

Whether one uses the tool or reinvents or reuses part of the
functionality is a different question than whether some functionality
itself is desirable or not, however.

> 2) If we did use libtool to build gcc, then, yes, I would be concerned
>    about the relinking issue.

Why?  Because of 'make install' run as root?  Any other reasons?

> 3) Shared libraries are less efficient.  You get some efficiency back if
>    the libraries are in fact shared by multiple different executables
>    running simultaneously.  But in this case it is relatively unlikely
>    that gmp, mpfr, and mpc will actually be used by any executable other
>    than gcc.

It is not so unlikely that multiple instances of cc1, cc1plus, and f951
are running simultaneously.  Granted, I haven't done any measurements.

>    So why make them shared libraries?  We lose something, as
>    can be seen by the number of times this has come up in gcc-help.  We
>    gain nothing.

Well, we *could* make hardcoding the default in order to cope with
gcc-help.[2]

> 4) People sometimes suggest seeing the DT_RPATH/DT_RUNPATH of the
>    executable to point to the shared library locations.  Past experience
>    has shown that this is a bad idea for some organizations.  Some
>    places mount /usr/local/lib or other directories over NFS.  Putting
>    that in DT_RPATH/DT_RUNPATH causes the dynamic linker to search those
>    directories at program startup.  That causes startup to be much
>    slower, and can even cause it to hang until the NFS server returns.
>    That is not desirable for the compiler.

Good points.

Thanks,
Ralf

[1] I'll hope you'll excuse me playing devil's advocate here.  ;-)
[2] Oops.  Twice in one message.