CLoadTags: Try accessing the first and last capability-size chunk

Check that we can access the first and last capability-size chunk.
This also ensures that the bad access address is updated correctly
in case any of these addresses are not accessible.
In theory we should try to access the entire memory region (to match what
sail does), but first and last will be equivalent for trapping/RVFI.

Previously we were just checking the tag memory, which returns 0 for
unmapped memory regions, but we should trap if these accesses are prevent
e.g. by the PMP.

target/cheri-common/op_helper_cheri_common.c

@@ -1607,8 +1607,18 @@ target_ulong CHERI_HELPER_IMPL(cloadtags(CPUArchState *env, uint32_t cb))
         cbp, sizealign, raise_unaligned_load_exception);
 
     target_ulong result = cheri_tag_get_many(env, addr, cb, NULL, GETPC());
+    /*
+     * Check that we can access the first and last capability-size chunk.
+     * This also ensures that the bad access address is updated correctly
+     * in case any of these addresses are not accessible.
+     * In theory we should try to access the entire memory region (to match what
+     * sail does), but first and last will be equivalent for trapping.
+     */
+    (void)cpu_ld_cap_word_ra(env, addr, _host_return_address);
+    (void)cpu_ld_cap_word_ra(env, addr + sizealign - CHERI_CAP_SIZE,
+                             _host_return_address);
 #if defined(TARGET_RISCV) && defined(CONFIG_RVFI_DII)
-    /* For RVFI tracing, sail reports the valu of th last capability read. */
+    /* For RVFI tracing, sail reports the value of the last capability read. */
     target_ulong unused1, unused2;
     (void)load_cap_from_memory_raw(env, &unused1, &unused2, cb, cbp,
                                    addr + sizealign - CHERI_CAP_SIZE,