PROBLEM: Personality flags not preserved across exec on Alpha

[Ulrich Mueller <ulm@xxxxxxxxxx>]

During investigation of an Alpha specific problem in GNU Emacs
(see https://bugs.gentoo.org/660448 and https://debbugs.gnu.org/32083)
we found that on Alpha the ADDR_NO_RANDOMIZE flag set with
personality(2) is not preserved across execve(2).

The following test program demonstrates the problem:

-------- 8< --------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/personality.h>

int
main (int argc, char **argv)
{
  int pers, new_pers;

  if ((pers = personality (0xffffffff)) < 0) {
    fprintf (stderr, "could not get personality\n");
    exit (1);
  }

  if (getenv ("WAS_HERE")) {
    printf ("*** after execvp ***\n");
    printf ("personality        = 0x%08x\n", pers);
    exit (0);
  }

  printf ("old personality    = 0x%08x\n", pers);

  new_pers = pers | ADDR_NO_RANDOMIZE;
  printf ("demand personality = 0x%08x\n", new_pers);

  if (personality (new_pers) < 0) {
    fprintf (stderr, "could not set personality\n");
    exit (1);
  }

  if ((pers = personality (0xffffffff)) < 0) {
    fprintf (stderr, "could not get personality\n");
    exit (1);
  }
  printf ("new personality    = 0x%08x\n", pers);

  putenv ("WAS_HERE=1");
  execvp (*argv, argv);

  fprintf (stderr, "execvp returned\n");
  exit (1);
}
-------- >8 --------

I get as output (on Alpha, kernel 4.17.0):

   old personality    = 0x00000000
   demand personality = 0x00040000
   new personality    = 0x00040000
   *** after execvp ***
   personality        = 0x00000000

Whereas on amd64 the last line is (as should be expected):

   personality        = 0x00040000


I suspect that the problem is with the SET_PERSONALITY macro defined
in arch/alpha/include/asm/elf.h:

#define SET_PERSONALITY(EX)                                     \
        set_personality(((EX).e_flags & EF_ALPHA_32BIT)         \
           ? PER_LINUX_32BIT : PER_LINUX)

The corresponding code for other architectures (e.g., ppc) does
additional masking of the flag bits, like this:

   set_personality(PER_LINUX | (current->personality & (~PER_MASK)))


Linux monolith 4.17.0+ #43 SMP Wed Jun 6 10:42:37 CEST 2018 alpha EV68AL Tsunami GNU/Linux

GNU C                   7.3.0
GNU Make                4.2.1
Binutils                2.30
Util-linux              2.32
Mount                   2.32
Module-init-tools       25
E2fsprogs               1.44.2
Linux C Library         2.27
Dynamic linker (ldd)    2.27
Linux C++ Library       6.0.24
Procps                  3.3.15
Net-tools               1.60
Kbd                     2.0.4
Console-tools           2.0.4
Sh-utils                8.30
Udev                    238
Modules Loaded          binfmt_misc cdrom libata netlink_diag pata_ali sr_mod unix_diag
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