Add a hybrid example related to threads

Check whether we can set DDCs for spawned threads individually, and
independent from the main program thread.

build/Makefile.vars.morello-hybrid

@@ -6,5 +6,5 @@
 
 CHERIBASE ?= $(HOME)/cheri
 SDKBASE ?= $(CHERIBASE)/output/morello-sdk
-CFLAGS := --config cheribsd-morello-hybrid.cfg $(CFLAGS)
+CFLAGS := --config cheribsd-morello-hybrid.cfg $(CFLAGS) -lm -lpthread
 PLATFORM := morello-hybrid

hybrid/threads_ddc.c

@@ -0,0 +1,73 @@
+/***
+ * This example explores setting different DDCs across threads, ensuring each
+ * thread has its own DDC which does not interfere with other threads.
+ *
+ * The number of threads to execute can be changed by modifying `t_count`.
+ ***/
+
+#include <assert.h>
+#include <math.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "cheriintrin.h"
+
+#include "../include/common.h"
+#include "./include/utils.h"
+
+struct t_info
+{
+    unsigned short count;
+    pthread_t tid;
+    void *addr_in;
+    void *__capability ddc_out;
+};
+
+void *run_thread(void *curr_t_info_ptr)
+{
+    struct t_info *curr_t_info = (struct t_info *) curr_t_info_ptr;
+    void *__capability old_ddc = read_ddc();
+    void *__capability new_ddc =
+        cheri_address_set(cheri_ddc_get(), (intptr_t) curr_t_info->addr_in);
+    write_ddc(new_ddc);
+    // Force wait to ensure threads don't die too fast
+    for (size_t i = 0; i < pow(10, 6); ++i)
+    {
+    };
+    curr_t_info->ddc_out = read_ddc();
+    assert(cheri_address_get(curr_t_info->ddc_out) == (unsigned long) curr_t_info->addr_in);
+    assert(curr_t_info->ddc_out != old_ddc);
+    return NULL;
+}
+
+int main()
+{
+    unsigned short t_count = 3;
+    const unsigned int to_alloc = 256;
+    struct t_info *t_infos = malloc(t_count * sizeof(struct t_info));
+    pthread_t *tids = malloc(t_count * sizeof(pthread_t));
+
+    for (size_t i = 0; i < t_count; ++i)
+    {
+        t_infos[i].count = i;
+        t_infos[i].addr_in = malloc(to_alloc);
+        pthread_create(&t_infos[i].tid, NULL, &run_thread, &t_infos[i]);
+    }
+
+    printf("== Main thread DDC:\n");
+    pp_cap(cheri_ddc_get());
+    for (size_t i = 0; i < t_count; ++i)
+    {
+        pthread_join(t_infos[i].tid, NULL);
+        printf("== From thread %hu:\n", t_infos[i].count);
+        pp_cap(t_infos[i].ddc_out);
+        free(t_infos[i].addr_in);
+    }
+
+    free(tids);
+    free(t_infos);
+    return 0;
+}

tests/run_tests.sh

@@ -88,6 +88,7 @@ elif [ "$1" = "morello-hybrid" ]; then
     run OK example_allocators/compartment_alloc main
     run OK hybrid basic_ddc
     run OK hybrid cap_build
+    run OK hybrid threads_ddc
     run OK hybrid/compartment_examples/inter_comp_call/base main
     run OK hybrid/compartment_examples/inter_comp_call/malicious_compartments inter_comp_call-secure
     run OK hybrid/ddc_compartment_switching ddc_compartment_switching