bug#20215: 25.0.50; Support compilation as PIE

bug#20215: 25.0.50; Support compilation as PIE

[Philipp Stephani]

Currently when trying to compile as a position-independent executable,
e.g.

./configure CFLAGS=-fPIE LDFLAGS=-pie && make

Emacs segfaults when dumping.



In GNU Emacs 25.0.50.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.8)
 of 2014-12-01 on touchstone.was.corp.google.com, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description:	Ubuntu 14.04 LTS

Configured using:
 `configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/25.0.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.0.50/site-lisp:/usr/share/emacs/site-lisp
 --with-crt-dir=/usr/lib/x86_64-linux-gnu --build x86_64-linux-gnu
 --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/25.0.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.0.50/site-lisp:/usr/share/emacs/site-lisp
 --with-crt-dir=/usr/lib/x86_64-linux-gnu --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fstack-protector --param=ssp-buffer-size=4 -Wformat
 -Werror=format-security -Wall' CPPFLAGS=-D_FORTIFY_SOURCE=2
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message dired format-spec
rfc822 mml easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util help-fns mail-prsvr mail-utils time-date tooltip
eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win
x-dnd tool-bar dnd fontset image regexp-opt fringe tabulated-list
newcomment elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax
facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak
czech european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer nadvice loaddefs button
faces cus-face macroexp files text-properties overlay sha1 md5 base64
format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process dbusbind gfilenotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty emacs)

Memory information:
((conses 16 76108 3865)
 (symbols 48 18176 0)
 (miscs 40 38 99)
 (strings 32 11196 4583)
 (string-bytes 1 304089)
 (vectors 16 10053)
 (vector-slots 8 395236 9639)
 (floats 8 72 61)
 (intervals 56 228 1)
 (buffers 976 11)
 (heap 1024 32389 968))

bug#20215: 25.0.50; Support compilation as PIE

[Stefan Monnier]

> Currently when trying to compile as a position-independent executable,
> e.g.

> ./configure CFLAGS=-fPIE LDFLAGS=-pie && make

> Emacs segfaults when dumping.

I have no idea why it would crash during the dumping process, but
I wouldn't be surprised if after a successful dump of `temacs', the
resulting `emacs' crashes early on, since the dump will be writing
a heap which will probably contain pointers back into the code.


        Stefan

bug#20215: 25.0.50; Support compilation as PIE

[Philipp Stephani]

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Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Fr., 27. März 2015 um
23:46 Uhr:

> > Currently when trying to compile as a position-independent executable,
> > e.g.
>
> > ./configure CFLAGS=-fPIE LDFLAGS=-pie && make
>
> > Emacs segfaults when dumping.
>
> I have no idea why it would crash during the dumping process, but
> I wouldn't be surprised if after a successful dump of `temacs', the
> resulting `emacs' crashes early on, since the dump will be writing
> a heap which will probably contain pointers back into the code.
>
>
>
I haven't investigated why it crashes in detail, but since the dumper
prevents ASLR and PIE (and doesn't work on platforms such as Chromium), I
think it should be replaced by a portable dumper.

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bug#20215: 25.0.50; Support compilation as PIE

[Stefan Monnier]

> ... it should be replaced by a portable dumper.

I think we all agree.


        Stefan "who also thinks that depending on the specifics of such
                a «portable» dumper, it may still break in the presence
                ASLR and friends"

bug#20215: 25.0.50; Support compilation as PIE

[Glenn Morris]

Version: 27.1

>> ... it should be replaced by a portable dumper.

And lo, it was.

Compiling with -fPIE seems to work with the portable dumper that will be
the default for Emacs 27.1 onwards.

bug#20215: acknowledged by developer (control message for bug #18784)

[Philipp Stephani]

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Could we please de-dupe this bug from the others? This bug is not about
adding -nopie to the Makefile, but about getting Emacs to work with -pie.

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