Bug#843198: gcc-6: Cross-compiles older GCC badly

[Matthew Gabeler-Lee <cheetah@fastcat.org>]

Package: gcc-6
Version: 6.2.0-11
Severity: normal

I'm working on a project that uses a Linaro gcc 4.8.3 cross compiler for
ARM, which I'm building on my Debian desktop.

As of gcc-6 6.2.0-6, this worked fine.

As of gcc-6 6.2.0-10, a subtly bad cross-compiler seems to be generated.  My
build is failing in an area related to precompiled headers:

cc1: warning: /path/to/foo.h.gch: had text segment at different address [enabled by default]
cc1: error: one or more PCH files were found, but they were invalid
cc1: fatal error: /path/to/foo.h: No such file or directory

I confirmed that if I downgrade all the binary packages I have installed
from the gcc-6 source to 6.2.0-6 and rebuild, things work again.

Scanning the changelogs, I came upon the idea that the default enabling of
-fPIE/-pie in 6.2.0-7 might have something to do with this, so I switched to
that version and tried again, and it failed, so at the very least the
problem is something that came in between the -6 and -7 releases.

Rebuilding the cross-toolchain with -fno-PIE -no-pie produced linker errors
complaining that it needed -fPIC, and rebuilding with -fno-PIE -no-pie -fPIC
produced the same errors, so I don't know what to do now :(

-- System Information:
Debian Release: stretch/sid
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.7.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages gcc-6 depends on:
ii  binutils      2.27.51.20161102-1
ii  cpp-6         6.2.0-6
ii  gcc-6-base    6.2.0-6
ii  libc6         2.24-5
ii  libcc1-0      6.2.0-6
ii  libgcc-6-dev  6.2.0-6
ii  libgcc1       1:6.2.0-6
ii  libgmp10      2:6.1.1+dfsg-1
ii  libisl15      0.17.1-1
ii  libmpc3       1.0.3-1
ii  libmpfr4      3.1.5-1
ii  libstdc++6    6.2.0-6
ii  zlib1g        1:1.2.8.dfsg-2+b3

Versions of packages gcc-6 recommends:
ii  libc6-dev  2.24-5

Versions of packages gcc-6 suggests:
ii  gcc-6-doc         6.1.0-1
pn  gcc-6-locales     <none>
pn  gcc-6-multilib    <none>
pn  libasan3-dbg      <none>
pn  libatomic1-dbg    <none>
pn  libcilkrts5-dbg   <none>
pn  libgcc1-dbg       <none>
pn  libgomp1-dbg      <none>
pn  libitm1-dbg       <none>
pn  liblsan0-dbg      <none>
pn  libmpx2-dbg       <none>
pn  libquadmath0-dbg  <none>
pn  libtsan0-dbg      <none>
pn  libubsan0-dbg     <none>

-- no debconf information