[2019-12] [threads] Add back mono_threads_attach_tools_thread as a public API (#18074)

[mono-project.git] / mono / utils / checked-build.c

/**
 * \file
 * Expensive asserts used when mono is built with --with-checked-build=yes
 *
 * Author:
 *      Rodrigo Kumpera (kumpera@gmail.com)
 *
 * (C) 2015 Xamarin
 */
#include <config.h>
#include <mono/utils/mono-compiler.h>

#ifdef ENABLE_CHECKED_BUILD

#include <mono/utils/checked-build.h>
#include <mono/utils/mono-threads.h>
#include <mono/utils/mono-threads-coop.h>
#include <mono/utils/mono-tls.h>
#include <mono/metadata/mempool.h>
#include <mono/metadata/metadata-internals.h>
#include <mono/metadata/image-internals.h>
#include <mono/metadata/loaded-images-internals.h>
#include <mono/metadata/class-internals.h>
#include <mono/metadata/reflection-internals.h>
#include <glib.h>

#ifdef HAVE_BACKTRACE_SYMBOLS
#include <execinfo.h>
#endif

// Selective-enable support

// Returns true for check modes which are allowed by both the current DISABLE_ macros and the MONO_CHECK_MODE env var.
// Argument may be a bitmask; if so, result is true if at least one specified mode is enabled.
mono_bool
mono_check_mode_enabled (MonoCheckMode query)
{
        static MonoCheckMode check_mode = MONO_CHECK_MODE_UNKNOWN;
        if (G_UNLIKELY (check_mode == MONO_CHECK_MODE_UNKNOWN))
        {
                MonoCheckMode env_check_mode = MONO_CHECK_MODE_NONE;
                gchar *env_string = g_getenv ("MONO_CHECK_MODE");

                if (env_string)
                {
                        gchar **env_split = g_strsplit (env_string, ",", 0);
                        for (gchar **env_component = env_split; *env_component; env_component++)
                        {
                                mono_bool check_all = g_str_equal (*env_component, "all");
#ifdef ENABLE_CHECKED_BUILD_GC
                                if (check_all || g_str_equal (*env_component, "gc"))
                                        env_check_mode |= MONO_CHECK_MODE_GC;
#endif
#ifdef ENABLE_CHECKED_BUILD_METADATA
                                if (check_all || g_str_equal (*env_component, "metadata"))
                                        env_check_mode |= MONO_CHECK_MODE_METADATA;
#endif
#ifdef ENABLE_CHECKED_BUILD_THREAD
                                if (check_all || g_str_equal (*env_component, "thread"))
                                        env_check_mode |= MONO_CHECK_MODE_THREAD;
#endif
                        }
                        g_strfreev (env_split);
                        g_free (env_string);
                }

                check_mode = env_check_mode;
        }
        return check_mode & query;
}

static int
mono_check_transition_limit (void)
{
        static int transition_limit = -1;
        if (transition_limit < 0) {
                gchar *env_string = g_getenv ("MONO_CHECK_THREAD_TRANSITION_HISTORY");
                if (env_string) {
                        transition_limit = atoi (env_string);
                        g_free (env_string);
                } else {
                        transition_limit = 3;
                }
        }
        return transition_limit;
}

#define MAX_NATIVE_BT 6
#define MAX_NATIVE_BT_PROBE (MAX_NATIVE_BT + 5)
#define MAX_TRANSITIONS (mono_check_transition_limit ())

typedef struct {
        const char *name;
        int from_state, next_state, suspend_count, suspend_count_delta, size;
        gpointer backtrace [MAX_NATIVE_BT_PROBE];
} ThreadTransition;

typedef struct {
        guint32 in_gc_critical_region;
        // ring buffer of transitions, indexed by two guint16 indices:
        // push at buf_end, iterate from buf_start. valid range is
        // buf_start ... buf_end - 1 mod MAX_TRANSITIONS
        gint32 ringbuf;
        ThreadTransition transitions [MONO_ZERO_LEN_ARRAY];
} CheckState;

static MonoNativeTlsKey thread_status;

static mono_mutex_t backtrace_mutex;


void
checked_build_init (void)
{
        // Init state for get_state, which can be called either by gc or thread mode
        if (mono_check_mode_enabled (MONO_CHECK_MODE_GC | MONO_CHECK_MODE_THREAD))
                mono_native_tls_alloc (&thread_status, NULL);
#if HAVE_BACKTRACE_SYMBOLS
        mono_os_mutex_init (&backtrace_mutex);
#endif
}

static gboolean
backtrace_mutex_trylock (void)
{
        return mono_os_mutex_trylock (&backtrace_mutex) == 0;
}

static void
backtrace_mutex_unlock (void)
{
        return mono_os_mutex_unlock (&backtrace_mutex);
}

static CheckState*
get_state (void)
{
        CheckState *state = (CheckState*)mono_native_tls_get_value (thread_status);
        if (!state) {
                state = (CheckState*) g_malloc0 (sizeof (CheckState) + sizeof(ThreadTransition) * MAX_TRANSITIONS);
                mono_native_tls_set_value (thread_status, state);
        }

        return state;
}

static void
ringbuf_unpack (gint32 ringbuf, guint16 *buf_start, guint16 *buf_end)
{
        *buf_start = (guint16) (ringbuf >> 16);
        *buf_end = (guint16) (ringbuf & 0x00FF);
}

static gint32
ringbuf_pack (guint16 buf_start, guint16 buf_end)
{
        return ((((gint32)buf_start) << 16) | ((gint32)buf_end));
}

static int
ringbuf_size (guint32 ringbuf, int n)
{
        guint16 buf_start, buf_end;
        ringbuf_unpack (ringbuf, &buf_start, &buf_end);
        if (buf_end > buf_start)
                return buf_end - buf_start;
        else
                return n - (buf_start - buf_end);
}

static guint16
ringbuf_push (gint32 *ringbuf, int n)
{
        gint32 ringbuf_old, ringbuf_new;
        guint16 buf_start, buf_end;
        guint16 cur;
retry:
        ringbuf_old = *ringbuf;
        ringbuf_unpack (ringbuf_old, &buf_start, &buf_end);
        cur = buf_end++;
        if (buf_end == n)
                buf_end = 0;
        if (buf_end == buf_start) {
                if (++buf_start == n)
                        buf_start = 0;
        }
        ringbuf_new = ringbuf_pack (buf_start, buf_end);
        if (mono_atomic_cas_i32 (ringbuf, ringbuf_new, ringbuf_old) != ringbuf_old)
                goto retry;
        return cur;
}

#ifdef ENABLE_CHECKED_BUILD_THREAD

#ifdef HAVE_BACKTRACE_SYMBOLS

//XXX We should collect just the IPs and lazily symbolificate them.
static int
collect_backtrace (gpointer out_data[])
{
#if defined (__GNUC__) && !defined (__clang__)
        /* GNU libc backtrace calls _Unwind_Backtrace in libgcc, which internally may take a lock. */
        /* Suppose we're using hybrid suspend and T1 is in GC Unsafe and T2 is
         * GC Safe.  T1 will be coop suspended, and T2 will be async suspended.
         * Suppose T1 is in RUNNING, and T2 just changed from RUNNING to
         * BLOCKING and it is in trace_state_change to record this fact.
         *
         * suspend initiator: switches T1 to ASYNC_SUSPEND_REQUESTED
         * suspend initiator: switches T2 to BLOCKING_SUSPEND_REQUESTED and sends a suspend signal
         * T1: calls mono_threads_transition_state_poll (),
         * T1: switches to SELF_SUSPENDED and starts trace_state_change ()
         * T2: is still in checked_build_thread_transition for the RUNNING->BLOCKING transition and calls backtrace ()
         * T2: suspend signal lands while T2 is in backtrace() holding a lock; T2 switches to BLOCKING_ASYNC_SUSPENDED () and waits for resume
         * T1: calls backtrace (), waits for the lock ()
         * suspend initiator: waiting for T1 to suspend.
         *
         * At this point we're deadlocked.
         *
         * So what we'll do is try to take a lock before calling backtrace and
         * only collect a backtrace if there is no contention.
         */
        int i;
        for (i = 0; i < 2; i++ ) {
                if (backtrace_mutex_trylock ()) {
                        int sz = backtrace (out_data, MAX_NATIVE_BT_PROBE);
                        backtrace_mutex_unlock ();
                        return sz;
                } else {
                        mono_thread_info_yield ();
                }
        }
        /* didn't get a backtrace, oh well. */
        return 0;
#else
        return backtrace (out_data, MAX_NATIVE_BT_PROBE);
#endif
}

static char*
translate_backtrace (gpointer native_trace[], int size)
{
        if (size == 0)
                return g_strdup ("");
        char **names = backtrace_symbols (native_trace, size);
        GString* bt = g_string_sized_new (100);

        int i, j = -1;

        //Figure out the cut point of useless backtraces
        //We'll skip up to the caller of checked_build_thread_transition
        for (i = 0; i < size; ++i) {
                if (strstr (names [i], "checked_build_thread_transition")) {
                        j = i + 1;
                        break;
                }
        }

        if (j == -1)
                j = 0;
        for (i = j; i < size; ++i) {
                if (i - j <= MAX_NATIVE_BT)
                        g_string_append_printf (bt, "\tat %s\n", names [i]);
        }

        g_free (names);
        return g_string_free (bt, FALSE);
}

#else

static int
collect_backtrace (gpointer out_data[])
{
        return 0;
}

static char*
translate_backtrace (gpointer native_trace[], int size)
{
        return g_strdup ("\tno backtrace available\n");
}

#endif

void
checked_build_thread_transition (const char *transition, void *info, int from_state, int suspend_count, int next_state, int suspend_count_delta, gboolean capture_backtrace)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_THREAD))
                return;

        /* We currently don't record external changes as those are hard to reason about. */
        if (!mono_thread_info_is_current ((THREAD_INFO_TYPE*)info))
                return;

        CheckState *state = get_state ();

        guint16 cur = ringbuf_push (&state->ringbuf, MAX_TRANSITIONS);

        ThreadTransition *t = &state->transitions[cur];
        t->name = transition;
        t->from_state = from_state;
        t->next_state = next_state;
        t->suspend_count = suspend_count;
        t->suspend_count_delta = suspend_count_delta;
        if (capture_backtrace)
                t->size = collect_backtrace (t->backtrace);
        else
                t->size = 0;
}

void
mono_fatal_with_history (const char * volatile msg, ...)
{
        GString* err = g_string_sized_new (100);

        g_string_append_printf (err, "Assertion failure in thread %p due to: ", mono_native_thread_id_get ());

        va_list args;
        va_start (args, msg);
        g_string_append_vprintf (err, msg, args);
        va_end (args);

        if (mono_check_mode_enabled (MONO_CHECK_MODE_THREAD))
        {
                CheckState *state = get_state ();
                guint16 cur, end;
                int len = ringbuf_size (state->ringbuf, MAX_TRANSITIONS);

                g_string_append_printf (err, "\nLast %d state transitions: (most recent first)\n", len);

                ringbuf_unpack (state->ringbuf, &cur, &end);
                while (cur != end) {
                        ThreadTransition *t = &state->transitions[cur];
                        char *bt = translate_backtrace (t->backtrace, t->size);
                        g_string_append_printf (err, "[%s] %s -> %s (%d) %s%d at:\n%s",
                                t->name,
                                mono_thread_state_name (t->from_state),
                                mono_thread_state_name (t->next_state),
                                t->suspend_count,
                                t->suspend_count_delta > 0 ? "+" : "", //I'd like to see this sort of values: -1, 0, +1
                                t->suspend_count_delta,
                                bt);
                        g_free (bt);
                        if (++cur == MAX_TRANSITIONS)
                                cur = 0;
                }
        }

        g_error (err->str);
        g_string_free (err, TRUE);
}

#endif /* defined(ENABLE_CHECKED_BUILD_THREAD) */

#ifdef ENABLE_CHECKED_BUILD_GC

void
assert_gc_safe_mode (const char *file, int lineno)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return;

        MonoThreadInfo *cur = mono_thread_info_current ();

        if (!cur)
                mono_fatal_with_history ("%s:%d: Expected GC Safe mode but thread is not attached", file, lineno);

        int state = mono_thread_info_current_state (cur);
        switch (state) {
        case STATE_BLOCKING:
        case STATE_BLOCKING_SELF_SUSPENDED:
        case STATE_BLOCKING_SUSPEND_REQUESTED:
                break;
        default:
                mono_fatal_with_history ("%s:%d: Expected GC Safe mode but was in %s state", file, lineno, mono_thread_state_name (state));
        }
}

void
assert_gc_unsafe_mode (const char *file, int lineno)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return;

        MonoThreadInfo *cur = mono_thread_info_current ();

        if (!cur)
                mono_fatal_with_history ("%s:%d: Expected GC Unsafe mode but thread is not attached", file, lineno);

        int state = mono_thread_info_current_state (cur);
        switch (state) {
        case STATE_RUNNING:
        case STATE_ASYNC_SUSPEND_REQUESTED:
                break;
        default:
                mono_fatal_with_history ("%s:%d: Expected GC Unsafe mode but was in %s state", file, lineno, mono_thread_state_name (state));
        }
}

void
assert_gc_neutral_mode (const char *file, int lineno)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return;

        MonoThreadInfo *cur = mono_thread_info_current ();

        if (!cur)
                mono_fatal_with_history ("%s:%d: Expected GC Neutral mode but thread is not attached", file, lineno);

        int state = mono_thread_info_current_state (cur);
        switch (state) {
        case STATE_RUNNING:
        case STATE_ASYNC_SUSPEND_REQUESTED:
        case STATE_BLOCKING:
        case STATE_BLOCKING_SELF_SUSPENDED:
        case STATE_BLOCKING_SUSPEND_REQUESTED:
                break;
        default:
                mono_fatal_with_history ("%s:%d: Expected GC Neutral mode but was in %s state", file, lineno, mono_thread_state_name (state));
        }
}

void *
critical_gc_region_begin(void)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return NULL;

        CheckState *state = get_state ();
        state->in_gc_critical_region++;
        return state;
}


void
critical_gc_region_end(void* token)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return;

        CheckState *state = get_state();
        g_assert (state == token);
        state->in_gc_critical_region--;
}

void
assert_not_in_gc_critical_region(void)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return;

        CheckState *state = get_state();
        if (state->in_gc_critical_region > 0) {
                mono_fatal_with_history("Expected GC Unsafe mode, but was in %s state", mono_thread_state_name (mono_thread_info_current_state (mono_thread_info_current ())));
        }
}

void
assert_in_gc_critical_region (void)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_GC))
                return;

        CheckState *state = get_state();
        if (state->in_gc_critical_region == 0)
                mono_fatal_with_history("Expected GC critical region");
}

#endif /* defined(ENABLE_CHECKED_BUILD_GC) */

#ifdef ENABLE_CHECKED_BUILD_METADATA

// check_metadata_store et al: The goal of these functions is to verify that if there is a pointer from one mempool into
// another, that the pointed-to memory is protected by the reference count mechanism for MonoImages.
//
// Note: The code below catches only some kinds of failures. Failures outside its scope notably incode:
// * Code below absolutely assumes that no mempool is ever held as "mempool" member by more than one Image or ImageSet at once
// * Code below assumes reference counts never underflow (ie: if we have a pointer to something, it won't be deallocated while we're looking at it)
// Locking strategy is a little slapdash overall.

// Reference audit support
#define check_mempool_assert_message(...) \
        g_assertion_message("Mempool reference violation: " __VA_ARGS__)

typedef struct
{
        MonoImage *image;
        MonoImageSet *image_set;
} MonoMemPoolOwner;

static MonoMemPoolOwner mono_mempool_no_owner = {NULL,NULL};

static gboolean
check_mempool_owner_eq (MonoMemPoolOwner a, MonoMemPoolOwner b)
{
        return a.image == b.image && a.image_set == b.image_set;
}

// Say image X "references" image Y if X either contains Y in its modules field, or X’s "references" field contains an
// assembly whose image is Y.
// Say image X transitively references image Y if there is any chain of images-referencing-images which leads from X to Y.
// Once the mempools for two pointers have been looked up, there are four possibilities:

// Case 1. Image FROM points to Image TO: Legal if FROM transitively references TO

// We'll do a simple BFS graph search on images. For each image we visit:
static void
check_image_search (GHashTable *visited, GPtrArray *next, MonoImage *candidate, MonoImage *goal, gboolean *success)
{
        // Image hasn't even been loaded-- ignore it
        if (!candidate)
                return;

        // Image has already been visited-- ignore it
        if (g_hash_table_lookup_extended (visited, candidate, NULL, NULL))
                return;

        // Image is the target-- mark success
        if (candidate == goal)
        {
                *success = TRUE;
                return;
        }

        // Unvisited image, queue it to have its children visited
        g_hash_table_insert (visited, candidate, NULL);
        g_ptr_array_add (next, candidate);
        return;
}

static gboolean
check_image_may_reference_image(MonoImage *from, MonoImage *to)
{
        if (to == from) // Shortcut
                return TRUE;

        // Corlib is never unloaded, and all images implicitly reference it.
        // Some images avoid explicitly referencing it as an optimization, so special-case it here.
        if (to == mono_defaults.corlib)
                return TRUE;

        // Non-dynamic images may NEVER reference dynamic images
        if (to->dynamic && !from->dynamic)
                return FALSE;

        // FIXME: We currently give a dynamic images a pass on the reference rules.
        // Dynamic images may ALWAYS reference non-dynamic images.
        // We allow this because the dynamic image code is known "messy", and in theory it is already
        // protected because dynamic images can only reference classes their assembly has retained.
        // However, long term, we should make this rigorous.
        if (from->dynamic && !to->dynamic)
                return TRUE;

        gboolean success = FALSE;

        // Images to inspect on this pass, images to inspect on the next pass
        GPtrArray *current = g_ptr_array_sized_new (1), *next = g_ptr_array_new ();

        // Because in practice the image graph contains cycles, we must track which images we've visited
        GHashTable *visited = g_hash_table_new (NULL, NULL);

        #define CHECK_IMAGE_VISIT(i) check_image_search (visited, next, (i), to, &success)

        CHECK_IMAGE_VISIT (from); // Initially "next" contains only from node

        // For each pass exhaust the "to check" queue while filling up the "check next" queue
        while (!success && next->len > 0) // Halt on success or when out of nodes to process
        {
                // Swap "current" and "next" and clear next
                GPtrArray *temp = current;
                current = next;
                next = temp;
                g_ptr_array_set_size (next, 0);

                int current_idx;
                for(current_idx = 0; current_idx < current->len; current_idx++)
                {
                        MonoImage *checking = (MonoImage*)g_ptr_array_index (current, current_idx);

                        mono_image_lock (checking);

                        // For each queued image visit all directly referenced images
                        int inner_idx;

                        // 'files' and 'modules' semantically contain the same items but because of lazy loading we must check both
                        for (inner_idx = 0; !success && inner_idx < checking->file_count; inner_idx++)
                        {
                                CHECK_IMAGE_VISIT (checking->files[inner_idx]);
                        }

                        for (inner_idx = 0; !success && inner_idx < checking->module_count; inner_idx++)
                        {
                                CHECK_IMAGE_VISIT (checking->modules[inner_idx]);
                        }

                        for (inner_idx = 0; !success && inner_idx < checking->nreferences; inner_idx++)
                        {
                                // Assembly references are lazy-loaded and thus allowed to be NULL.
                                // If they are NULL, we don't care about them for this search, because their images haven't impacted ref_count yet.
                                if (checking->references[inner_idx])
                                {
                                        CHECK_IMAGE_VISIT (checking->references[inner_idx]->image);
                                }
                        }

                        mono_image_unlock (checking);
                }
        }

        g_ptr_array_free (current, TRUE); g_ptr_array_free (next, TRUE); g_hash_table_destroy (visited);

        return success;
}

// Case 2. ImageSet FROM points to Image TO: One of FROM's "images" either is, or transitively references, TO.
static gboolean
check_image_set_may_reference_image (MonoImageSet *from, MonoImage *to)
{
        // See above-- All images implicitly reference corlib
        if (to == mono_defaults.corlib)
                return TRUE;

        int idx;
        gboolean success = FALSE;
        mono_image_set_lock (from);
        for (idx = 0; !success && idx < from->nimages; idx++)
        {
                if (check_image_may_reference_image (from->images[idx], to))
                        success = TRUE;
        }
        mono_image_set_unlock (from);

        return success; // No satisfying image found in from->images
}

// Case 3. ImageSet FROM points to ImageSet TO: The images in TO are a strict subset of FROM (no transitive relationship is important here)
static gboolean
check_image_set_may_reference_image_set (MonoImageSet *from, MonoImageSet *to)
{
        if (to == from)
                return TRUE;

        gboolean valid = TRUE; // Until proven otherwise

        mono_image_set_lock (from); mono_image_set_lock (to);

        int to_idx, from_idx;
        for (to_idx = 0; valid && to_idx < to->nimages; to_idx++)
        {
                gboolean seen = FALSE;

                // If TO set includes corlib, the FROM set may
                // implicitly reference corlib, even if it's not
                // present in the set explicitly.
                if (to->images[to_idx] == mono_defaults.corlib)
                        seen = TRUE;

                // For each item in to->images, scan over from->images seeking a path to it.
                for (from_idx = 0; !seen && from_idx < from->nimages; from_idx++)
                {
                        if (check_image_may_reference_image (from->images[from_idx], to->images[to_idx]))
                                seen = TRUE;
                }

                // If the to->images item is not found in from->images, the subset check has failed
                if (!seen)
                        valid = FALSE;
        }

        mono_image_set_unlock (from); mono_image_set_unlock (to);

        return valid; // All items in "to" were found in "from"
}

// Case 4. Image FROM points to ImageSet TO: FROM transitively references *ALL* of the “images” listed in TO
static gboolean
check_image_may_reference_image_set (MonoImage *from, MonoImageSet *to)
{
        if (to->nimages == 0) // Malformed image_set
                return FALSE;

        gboolean valid = TRUE;

        mono_image_set_lock (to);
        int idx;
        for (idx = 0; valid && idx < to->nimages; idx++)
        {
                if (!check_image_may_reference_image (from, to->images[idx]))
                        valid = FALSE;
        }
        mono_image_set_unlock (to);

        return valid; // All images in to->images checked out
}

// Small helper-- get a descriptive string for a MonoMemPoolOwner
// Callers are obligated to free buffer with g_free after use
static const char *
check_mempool_owner_name (MonoMemPoolOwner owner)
{
        GString *result = g_string_new (NULL);
        if (owner.image)
        {
                if (owner.image->dynamic)
                        g_string_append (result, "(Dynamic)");
                g_string_append (result, owner.image->name);
        }
        else if (owner.image_set)
        {
                char *temp = mono_image_set_description (owner.image_set);
                g_string_append (result, "(Image set)");
                g_string_append (result, temp);
                g_free (temp);
        }
        else
        {
                g_string_append (result, "(Non-image memory)");
        }
        return g_string_free (result, FALSE);
}

// Helper -- surf various image-locating functions looking for the owner of this pointer
static MonoMemPoolOwner
mono_find_mempool_owner (void *ptr)
{
        MonoMemPoolOwner owner = mono_mempool_no_owner;

        owner.image = mono_find_image_owner (ptr);
        if (!check_mempool_owner_eq (owner, mono_mempool_no_owner))
                return owner;

        owner.image_set = mono_find_image_set_owner (ptr);
        if (!check_mempool_owner_eq (owner, mono_mempool_no_owner))
                return owner;

        owner.image = mono_find_dynamic_image_owner (ptr);

        return owner;
}

// Actually perform reference audit
static void
check_mempool_may_reference_mempool (void *from_ptr, void *to_ptr, gboolean require_local)
{
        if (!mono_check_mode_enabled (MONO_CHECK_MODE_METADATA))
                return;

        // Null pointers are OK
        if (!to_ptr)
                return;

        MonoMemPoolOwner from = mono_find_mempool_owner (from_ptr), to = mono_find_mempool_owner (to_ptr);

        if (require_local)
        {
                if (!check_mempool_owner_eq (from,to))
                        check_mempool_assert_message ("Pointer in image %s should have been internal, but instead pointed to image %s", check_mempool_owner_name (from), check_mempool_owner_name (to));
        }

        // Writing into unknown mempool
        else if (check_mempool_owner_eq (from, mono_mempool_no_owner))
        {
                check_mempool_assert_message ("Non-image memory attempting to write pointer to image %s", check_mempool_owner_name (to));
        }

        // Reading from unknown mempool
        else if (check_mempool_owner_eq (to, mono_mempool_no_owner))
        {
                check_mempool_assert_message ("Attempting to write pointer from image %s to non-image memory", check_mempool_owner_name (from));
        }

        // Split out the four cases described above:
        else if (from.image && to.image)
        {
                if (!check_image_may_reference_image (from.image, to.image))
                        check_mempool_assert_message ("Image %s tried to point to image %s, but does not retain a reference", check_mempool_owner_name (from), check_mempool_owner_name (to));
        }

        else if (from.image && to.image_set)
        {
                if (!check_image_may_reference_image_set (from.image, to.image_set))
                        check_mempool_assert_message ("Image %s tried to point to image set %s, but does not retain a reference", check_mempool_owner_name (from), check_mempool_owner_name (to));
        }

        else if (from.image_set && to.image_set)
        {
                if (!check_image_set_may_reference_image_set (from.image_set, to.image_set))
                        check_mempool_assert_message ("Image set %s tried to point to image set %s, but does not retain a reference", check_mempool_owner_name (from), check_mempool_owner_name (to));
        }

        else if (from.image_set && to.image)
        {
                if (!check_image_set_may_reference_image (from.image_set, to.image))
                        check_mempool_assert_message ("Image set %s tried to point to image %s, but does not retain a reference", check_mempool_owner_name (from), check_mempool_owner_name (to));
        }

        else
        {
                check_mempool_assert_message ("Internal logic error: Unreachable code");
        }
}

void
check_metadata_store (void *from, void *to)
{
    check_mempool_may_reference_mempool (from, to, FALSE);
}

void
check_metadata_store_local (void *from, void *to)
{
    check_mempool_may_reference_mempool (from, to, TRUE);
}

#endif /* defined(ENABLE_CHECKED_BUILD_METADATA) */
#else /* ENABLE_CHECKED_BUILD */

MONO_EMPTY_SOURCE_FILE (checked_build);
#endif /* ENABLE_CHECKED_BUILD */