[glibc/arm/morello/main] cheri: don't use dl_random for pointer mangling

[Szabolcs Nagy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=72aca7d8eb54c2a44b2d1b13e5b84dc874241c1e

commit 72aca7d8eb54c2a44b2d1b13e5b84dc874241c1e
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Tue Mar 1 17:36:12 2022 +0000

    cheri: don't use dl_random for pointer mangling
    
    Pointer mangling cannot be supported on capability architectures.
    And there is not enough bytes in dl_random for 128 bit pointers.
    
    Stack guard is still loaded from dl_random: stack protection is
    unlikely to be useful on a capability architecture, but it works.

Diff:
---
 sysdeps/unix/sysv/linux/dl-osinfo.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/dl-osinfo.h b/sysdeps/unix/sysv/linux/dl-osinfo.h
index 49d8f973c8..c5d864f5ba 100644
--- a/sysdeps/unix/sysv/linux/dl-osinfo.h
+++ b/sysdeps/unix/sysv/linux/dl-osinfo.h
@@ -52,7 +52,12 @@ _dl_setup_stack_chk_guard (void *dl_random)
 static inline uintptr_t __attribute__ ((always_inline))
 _dl_setup_pointer_guard (void *dl_random, uintptr_t stack_chk_guard)
 {
+#ifdef __CHERI_PURE_CAPABILITY__
+  /* Pointer mangling is not supported on capability architectures.  */
+  return 0;
+#else
   uintptr_t ret;
   memcpy (&ret, (char *) dl_random + sizeof (ret), sizeof (ret));
   return ret;
+#endif
 }