[glibc/arm/morello/main] cheri: rseq: remove const to avoid readonly permission

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1b8d019265ebe0b6c27a8e845de3127449956dd6

commit 1b8d019265ebe0b6c27a8e845de3127449956dd6
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Tue Mar 1 09:44:14 2022 +0000

    cheri: rseq: remove const to avoid readonly permission
    
    Using const on the definition does not work for a pure capability ABI:
    the capability permissions when accessing the object will be read only.
    
    Use a hack to hide the public declaration in the TU where the const
    objects are initialized. (This should work on non-capability targets
    too, but to err on the safe side only enable the hack on capability
    targets.)

Diff:
---
 sysdeps/nptl/dl-tls_init_tp.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c
index 53fba774a5..e4d7bb71ad 100644
--- a/sysdeps/nptl/dl-tls_init_tp.c
+++ b/sysdeps/nptl/dl-tls_init_tp.c
@@ -16,6 +16,15 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+#ifdef __CHERI_PURE_CAPABILITY__
+/* This hack ensures that the later indirectly included public const
+   declaration does not conflict with the non-const definition here.  */
+# define __rseq_size __rseq_size_public_const
+# define __rseq_offset __rseq_offset_public_const
+# include <sys/rseq.h>
+# undef __rseq_size
+# undef __rseq_offset
+#endif
 #include <kernel-features.h>
 #include <ldsodefs.h>
 #include <list.h>
@@ -45,8 +54,13 @@ rtld_mutex_dummy (pthread_mutex_t *lock)
 #endif
 
 const unsigned int __rseq_flags;
+#ifdef __CHERI_PURE_CAPABILITY__
+unsigned int __rseq_size attribute_relro;
+ptrdiff_t __rseq_offset attribute_relro;
+#else
 const unsigned int __rseq_size attribute_relro;
 const ptrdiff_t __rseq_offset attribute_relro;
+#endif
 
 void
 __tls_pre_init_tp (void)