RFC: Add --enable-static-pie to build static executables as PIE

[Alan Modra]

On Tue, Jul 18, 2017 at 05:30:48AM -0700, H.J. Lu wrote:
> On Mon, Jul 17, 2017 at 9:25 PM, Alan Modra <amodra@gmail.com> wrote:
> > On Mon, Jul 17, 2017 at 03:57:47PM -0700, H.J. Lu wrote:
> >> On Mon, Jul 17, 2017 at 3:29 PM, Rich Felker <dalias@libc.org> wrote:
> >> > On Mon, Jul 17, 2017 at 08:58:22AM -0700, H.J. Lu wrote:
> >> >> Hi,
> >> >>
> >> >> Are there any interests for --enable-static-pie, which builds static
> >> >> executables as PIE?
> >> >
> >> > Can you clarify what you're asking about? Is this asking if glibc is
> >> > interested in providing the runtime support (crt variant) for gcc to
> >> > be able to produce static PIE executables using glibc? I'm unclear on
> >> > whose configure script would need --enable-static-pie.
> >> >
> >>
> >> --enable-static-pie will be a configure option to glibc:
> >>
> >> 1. Build libc.a with -fPIE.
> >> 2. Update pointers in static PIE.
> >> 3. Apply IREL relocations for static PIE.
> >> 4 ....
> >
> > Explain first exactly what you mean by a "static PIE".
> >
> > - Will it be ET_EXEC or ET_DYN?
> 
> [hjl@gnu-tools-1 build-x86_64-linux]$ readelf -h elf/sln
> ELF Header:
>   Magic:   7f 45 4c 46 02 01 01 03 00 00 00 00 00 00 00 00
>   Class:                             ELF64
>   Data:                              2's complement, little endian
>   Version:                           1 (current)
>   OS/ABI:                            UNIX - GNU
>   ABI Version:                       0
>   Type:                              DYN (Shared object file)

OK, good.  I don't have any problem with this.

Now, you can link PIEs using -fPIE static libraries just with "-pie
-Wl,-Bstatic".  This will give you a PIE with no dynamic library
dependencies (except ld.so) and needs no toolchain or startup file
changes.  You only need to ensure that libc.a and other archives are
built with -fPIE.

> Linker needs to support --no-dynamic-linker.

Is there really much to be gained from PIEs that don't use ld.so
versus those that do?

-- 
Alan Modra
Australia Development Lab, IBM