Subject: Porting emacs-25 to GNU/Linux ppc64 with draft glibc 2.24
From: Paul Eggert <[email-masked]>
To: [email-masked]
Date: Wed, 20 Jul 2016 10:02:32 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

Tags: patch

I'd like to backport the attached patch from master to emacs-25. The 
idea is that Emacs 25 should work with glibc 2.24 (which is still in 
draft form). glibc is withdrawing support for some deprecated symbols 
like malloc_set_state and __malloc_initialize_hook. Emacs is intended to 
be portable to systems lacking these symbols, but this apparently does 
not work on ppc64 and ppc64le platforms. As noted in 
<https://sourceware.org/ml/libc-alpha/2016-07/msg00546.html>, the 
attached patch has been tested on emacs-25 and works on the affected 
platforms. I've also tested it on unaffected platforms such as x86 and 
x86-64.

This issue may be a release blocker for glibc 2.24 (this still hasn't 
been decided). I'd rather that Emacs didn't get in the way of the malloc 
performance improvements intended for glibc 2.24, and installing this 
patch into emacs-25 should help with that.

From 418fa48309e1886fe5e611fa07acf193f5e3f7f9 Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email-masked]>
Date: Tue, 19 Jul 2016 15:23:14 +0200
Subject: [PATCH] Port to glibc 2.24 (pre-release) + ppc64

Backport from master.
Inspired by a suggestion by Florian Weimer in:
https://sourceware.org/ml/libc-alpha/2016-07/msg00425.html
* configure.ac (HAVE_PERSONALITY_ADDR_NO_RANDOMIZE):
Rename from HAVE_PERSONALITY_LINUX32, and check for
ADDR_NO_RANDOMIZE (the crucial thing) instead of for LINUX32.
All uses changed.
* src/emacs.c (main) [HAVE_PERSONALITY_ADDR_NO_RANDOMIZE]:
Use ADDR_NO_RANDOMIZE from personality.h rather than inventing the
flag ourselves.  Just set that flag, rather than also setting the
persona.  Do all this earlier, so as to avoid problems with calls
to brk in the interim.  When doing it, avoid functions like
putenv that may allocate memory.  Special case for __PPC64__,
which needs ASLR disabled in dumped Emacs too.
---
 admin/CPP-DEFINES |  2 +-
 configure.ac      | 20 +++++++++++---------
 src/emacs.c       | 53 ++++++++++++++++++++++++++++++-----------------------
 3 files changed, 42 insertions(+), 33 deletions(-)

diff --git a/admin/CPP-DEFINES b/admin/CPP-DEFINES
index 796b57d..d404dee 100644
--- a/admin/CPP-DEFINES
+++ b/admin/CPP-DEFINES
@@ -237,7 +237,7 @@ HAVE_NET_IF_DL_H
 HAVE_NET_IF_H
 HAVE_NLIST_H
 HAVE_OTF_GET_VARIATION_GLYPHS
-HAVE_PERSONALITY_LINUX32
+HAVE_PERSONALITY_ADDR_NO_RANDOMIZE
 HAVE_PNG
 HAVE_PNG_H
 HAVE_POSIX_MEMALIGN
diff --git a/configure.ac b/configure.ac
index 678e98e..9da23d1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1615,15 +1615,17 @@ AC_CHECK_HEADERS_ONCE(
   sys/resource.h
   sys/utsname.h pwd.h utmp.h util.h)
 
-AC_MSG_CHECKING(if personality LINUX32 can be set)
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/personality.h>]], [[personality (PER_LINUX32)]])],
-               emacs_cv_personality_linux32=yes,
-	       emacs_cv_personality_linux32=no)
-AC_MSG_RESULT($emacs_cv_personality_linux32)
-
-if test $emacs_cv_personality_linux32 = yes; then
-  AC_DEFINE(HAVE_PERSONALITY_LINUX32, 1,
-            [Define to 1 if personality LINUX32 can be set.])
+AC_CACHE_CHECK([if personality ADDR_NO_RANDOMIZE flag exists],
+  [emacs_cv_personality_addr_no_randomize],
+  [AC_COMPILE_IFELSE(
+     [AC_LANG_PROGRAM([[#include <sys/personality.h>]],
+		      [[personality (personality (0xffffffff)
+				     | ADDR_NO_RANDOMIZE)]])],
+     [emacs_cv_personality_addr_no_randomize=yes],
+     [emacs_cv_personality_addr_no_randomize=no])])
+if test $emacs_cv_personality_addr_no_randomize = yes; then
+  AC_DEFINE([HAVE_PERSONALITY_ADDR_NO_RANDOMIZE], [1],
+            [Define to 1 if personality flag ADDR_NO_RANDOMIZE exists.])
 fi
 
 # Note that Solaris has sys/sysinfo.h which defines struct
diff --git a/src/emacs.c b/src/emacs.c
index 5c187e7..b0e5a05 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -106,7 +106,7 @@ extern void moncontrol (int mode);
 #include <sys/resource.h>
 #endif
 
-#ifdef HAVE_PERSONALITY_LINUX32
+#ifdef HAVE_PERSONALITY_ADDR_NO_RANDOMIZE
 #include <sys/personality.h>
 #endif
 
@@ -674,6 +674,35 @@ main (int argc, char **argv)
 
   stack_base = &dummy;
 
+  dumping = !initialized && (strcmp (argv[argc - 1], "dump") == 0
+			     || strcmp (argv[argc - 1], "bootstrap") == 0);
+
+#ifdef HAVE_PERSONALITY_ADDR_NO_RANDOMIZE
+
+  /* True if address randomization interferes with memory allocaiton.  */
+# ifdef __PPC64__
+  bool disable_aslr = true;
+# else
+  bool disable_aslr = dumping;
+# endif
+
+  if (disable_aslr)
+    {
+      int pers = personality (0xffffffff);
+      if (! (pers & ADDR_NO_RANDOMIZE)
+	  && 0 <= personality (pers | ADDR_NO_RANDOMIZE))
+	{
+	  /* Address randomization was enabled, but is now disabled.
+	     Re-execute Emacs to get a clean slate.  */
+	  execvp (argv[0], argv);
+
+	  /* If the exec fails, warn the user and then try without a
+	     clean slate.  */
+	  fprintf (stderr, "%s: %s\n", argv[0], strerror (errno));
+	}
+    }
+#endif
+
 #ifndef CANNOT_DUMP
   might_dump = !initialized;
 #endif
@@ -781,28 +810,6 @@ main (int argc, char **argv)
         }
     }
 
-  dumping = !initialized && (strcmp (argv[argc - 1], "dump") == 0
-			     || strcmp (argv[argc - 1], "bootstrap") == 0);
-
-#ifdef HAVE_PERSONALITY_LINUX32
-  if (dumping && ! getenv ("EMACS_HEAP_EXEC"))
-    {
-      /* Set this so we only do this once.  */
-      xputenv ("EMACS_HEAP_EXEC=true");
-
-      /* A flag to turn off address randomization which is introduced
-         in linux kernel shipped with fedora core 4 */
-#define ADD_NO_RANDOMIZE 0x0040000
-      personality (PER_LINUX32 | ADD_NO_RANDOMIZE);
-#undef  ADD_NO_RANDOMIZE
-
-      execvp (argv[0], argv);
-
-      /* If the exec fails, try to dump anyway.  */
-      emacs_perror (argv[0]);
-    }
-#endif /* HAVE_PERSONALITY_LINUX32 */
-
 #if defined (HAVE_SETRLIMIT) && defined (RLIMIT_STACK) && !defined (CYGWIN)
   /* Extend the stack space available.  Don't do that if dumping,
      since some systems (e.g. DJGPP) might define a smaller stack
-- 
2.5.5