c18n: Push dummy frame during _rtld_tlsdesc_dynamic

The dummy frame indicates that the current compartment is RTLD. Because
_rtld_tlsdesc_dynamic may cause domain transition (e.g., locking), a
frame that correctly identifies the current compartment as RTLD is
necessary.

libexec/rtld-elf/aarch64/rtld_start.S

@@ -380,13 +380,11 @@ ENTRY(C18N_SYM(_rtld_tlsdesc_dynamic))
 	 * get the caller's old stack top.
 	 */
 	update_stk_table	c11, c10, w12
-#ifdef __ARM_MORELLO_PURECAP_BENCHMARK_ABI
 	/*
 	 * Switch to RTLD's stack.
 	 */
 	get_rtld_stk		c10
 	set_untrusted_stk	c10
-#endif
 	/*
 	 * Save caller's old stack top.
 	 */

libexec/rtld-elf/rtld.c

@@ -5750,13 +5750,26 @@ void *
 tls_get_addr_common(uintptr_t **dtvp, int index, size_t offset)
 {
 	uintptr_t *dtv;
+	void *ret;
 
 	dtv = *dtvp;
 	/* Check dtv generation in case new modules have arrived */
 	if (__predict_true(dtv[0] == tls_dtv_generation &&
 	    dtv[index + 1] != 0))
 		return ((void *)(dtv[index + 1] + offset));
-	return (tls_get_addr_slow(dtvp, index, offset, false));
+
+#if defined(__CHERI_PURE_CAPABILITY__) && defined(RTLD_SANDBOX)
+	struct trusted_frame *tf;
+
+	if (C18N_ENABLED)
+		tf = push_dummy_rtld_trusted_frame(get_trusted_stk());
+#endif
+	ret = tls_get_addr_slow(dtvp, index, offset, false);
+#if defined(__CHERI_PURE_CAPABILITY__) && defined(RTLD_SANDBOX)
+	if (C18N_ENABLED)
+		tf = pop_dummy_rtld_trusted_frame(tf);
+#endif
+	return (ret);
 }
 
 #ifdef TLS_VARIANT_I