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Re: Why GLIBC requires compiler optimizations to build
On 20 June 2018 at 13:51, Carlos O'Donell <carlos@redhat.com> wrote:
> On 06/20/2018 06:35 AM, Gary Benson wrote:
> > On 11 June 2018 at 22:48, H.J. Lu <hjl.tools@gmail.com> wrote:
> > > On Mon, Jun 11, 2018 at 2:38 PM, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:
> > > > It has been some time since I tried to build glibc without optimization
> > > > as an exercise and I can't really recall what exactly has prevented me
> > > > to accomplish it. So the question is if it is make sense to add such
> > > > requirement and if it is the case whether it would be a useful options
> > > > and what prevents us to do so?
> > >
> > > The main issue is to bootstrap ld.so to prevent dynamic relocations
> > > before it is ready.
> >
> > Is it only really elf/rtld.c that specifically requires optimization then?
>
> No.
>
> The dynamic loader has many functions it needs to execute the early startup.
>
> So there are a lot of dependencies on other *.c files here and there, which
> must be callable directly and not through the PLT.
Ok. Thanks for explaining this.
> The perfect solution is a refactored build system that can distinguish what
> is going into rtld that needs optimizations and what is not. Then apply
> optimizations only to rtld.
>
> Even then, for debugging purposes, I have gotten away with using gcc's
> function attributes to mark some function as -O0 to debug them more easily,
> otherwise it's very hard to debug and _dl_debug_printf() is your highest
> value tool.
I did not know about __attribute__ ((optimize ())), thank you!
Gary