[glibc/arm/morello/main] TODO(gcc): cheri: work around a gcc bug in _dl_setup_stack_chk_guard

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=465880458a62761b9e976e49403485929634ebe9

commit 465880458a62761b9e976e49403485929634ebe9
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Fri Jul 15 19:33:23 2022 +0100

    TODO(gcc): cheri: work around a gcc bug in _dl_setup_stack_chk_guard
    
    morello purecap gcc in some cases inlines 16byte memcpy as a capability
    load, which is wrong if the source or dest may be unaligned.
    
    stack guard only needs random for the address portion since only that
    part is compared, so 8 byte is enough with 64 bit addresses, but the
    current code is only right on little endian systems.
    
    TODO: drop when gcc is fixed

Diff:
---
 sysdeps/unix/sysv/linux/dl-osinfo.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/dl-osinfo.h b/sysdeps/unix/sysv/linux/dl-osinfo.h
index 7888915f12..49d8f973c8 100644
--- a/sysdeps/unix/sysv/linux/dl-osinfo.h
+++ b/sysdeps/unix/sysv/linux/dl-osinfo.h
@@ -34,7 +34,11 @@ _dl_setup_stack_chk_guard (void *dl_random)
   /* We need in the moment only 8 bytes on 32-bit platforms and 16
      bytes on 64-bit platforms.  Therefore we can use the data
      directly and not use the kernel-provided data to seed a PRNG.  */
+#ifdef __CHERI_PURE_CAPABILITY__
+  memcpy (ret.bytes, dl_random, 8);
+#else
   memcpy (ret.bytes, dl_random, sizeof (ret));
+#endif
 #if BYTE_ORDER == LITTLE_ENDIAN
   ret.num &= ~(uintptr_t) 0xff;
 #elif BYTE_ORDER == BIG_ENDIAN