Implement object address discovery from an interior pointer in the public MPS

code/addrobj.c

@@ -0,0 +1,240 @@
+/* addrobj.c: BASE ADDRESS FROM INTERIOR POINTER TEST
+ *
+ * Copyright (c) 2023 Ravenbrook Limited. See end of file for license.
+ *
+ * .overview This test is for mps_addr_object(). Its intention is to
+ * verify that the function returns the appropriate base pointer to an
+ * object when provided with an interior pointer. It also tests that the
+ * function fails appropriately when the provided with a pointer to
+ * unmanaged memory, or to an object in a pool that doesn't support this
+ * feature.
+ *
+ * .limitations Objects that have been moved should cause the function to
+ * fail with MPS_RES_FAIL, however this is not tested. It could be tested if
+ * a testbench deliberately created a forwarding object, however this might
+ * confuse a pool that does automatic garbage collection such as AMC or AMCZ,
+ * so any such test would need to be designed to handle that.
+ * This test only examines behaviour in AMCZ and MVFF pools, i.e. A pool (AMCZ)
+ * which currently implements mps_addr_object() and one (MVFF) that doesn't.
+ */
+
+#include "mps.h"
+#include "testlib.h"
+#include "fmtdy.h"
+#include "fmtdytst.h"
+#include "mpsavm.h"
+#include "mpscamc.h"
+#include "mpscmvff.h"
+#include "stdio.h"
+#include <stdlib.h>
+
+/* Define an object size to allocate. The size chosen doesn't matter much, except that this testbench assumes
+   that the object is large enough that a pointer could point to the interior of the object, without also
+   pointing to the base pointer of the object at the same time. For char pointers, this is probably 2 bytes.
+   Since we are using the Dylan library, we define the size of the object in terms of Dylan slots. See
+   fmtdytst.c for details of the Dylan object structure.*/
+#define N_SLOT_TESTOBJ 100
+
+static void test_main(void)
+{
+  mps_arena_t arena;
+  mps_pool_t amcz_pool, mvff_pool;
+  mps_ap_t obj_ap;
+  mps_fmt_t obj_fmt;
+  mps_root_t testobj_root;
+  mps_res_t res;
+  /* In another testbench (extcon.c) we observed unreliable failures to do with registering the cold end
+     of the stack.  See GitHub issue #210
+     <https://github.com/Ravenbrook/mps/issues/210>.  For now, we
+     declare this as a separate root. */
+  static mps_addr_t testobj;
+  mps_addr_t out, in;
+
+  /* Create arena */
+  die(mps_arena_create_k(&arena, mps_arena_class_vm(), mps_args_none), "mps_arena_create_k");
+
+
+  /* INTRO TO TESTS: There are several tests. They test the expected "normal" operation of the
+     function, using an interior pointer, also corner cases where the interior pointer equals the
+     base pointer, where it equals the limit pointer. We also test asking about an address in unmanaged
+     memory, and about an address in a pool which currently does not support mps_addr_object. If you write
+     more tests, describe them here.*/
+
+
+  /* TEST 1: Test using an interior pointer in an object in an AMCZ pool.
+     At the time of writing this test, the AMCZ pool is the only pool where
+     there exists a requirement to provide base addresses from interior pointers.
+     Currently, the AMCZ pool (and by extension, the AMC pool which shares the same
+     module as AMCZ) is the only pool for which mps_addr_object is implemented */
+
+  /* Use the dylan format for convenience */
+  die(dylan_fmt(&obj_fmt, arena), "dylan_fmt");
+
+  /* Create the pool */
+  MPS_ARGS_BEGIN(args) {
+    MPS_ARGS_ADD(args, MPS_KEY_FORMAT, obj_fmt);
+    die(mps_pool_create_k(&amcz_pool, arena, mps_class_amcz(), args), "mps_pool_create_k amcz");
+  } MPS_ARGS_END(args);
+
+  /* Create an area of ambiguous pointers to keep the object alive and in place, in this case
+     the area only contains room for a single reference since we are only using one object to test */
+  die(mps_root_create_area(&testobj_root, arena,
+                           mps_rank_ambig(), (mps_rm_t)0,
+                           &testobj, &testobj+1,
+                           mps_scan_area, NULL),
+          "mps_root_create_area");
+
+  /* Create the allocation point */
+  die(mps_ap_create_k(&obj_ap, amcz_pool, mps_args_none), "mps_ap_create_k");
+
+  /* Make a Dylan object, size = (N_SLOT_TESTOBJ+2) * sizeof(mps_word_t).
+     (See fmtdytst.c for size calculation) */
+  {
+    /* Because make_dylan_vector returns its pointer-to-object as an mps_word_t rather than an
+       mps_addr_t, and commits the object, we need to somehow safely allocate our object without
+       type punning and without risking that our object be destroyed.
+       Rather than redefine our reference table with type mps_word_t, which hides the intention of the table,
+       park the arena to disable garbage collection. Allocate our dylan object on the (unregistered) stack
+       storing its address in an mps_word_t. Then store this mps_word_t as an mps_addr_t in our reference
+       table, and release the arena since our object is now safely pinned.
+       Another approach would be to create another static registered root for ambiguous references of type
+       mps_word_t and then copy to the mps_addr_t root, which would avoid needing to park the arena.
+    */
+    mps_word_t p_word;
+    mps_arena_park(arena);
+    die(make_dylan_vector(&p_word, obj_ap, N_SLOT_TESTOBJ), "make_dylan_vector");
+    /* If we hadn't parked the arena, our vector might have been GC'd here */
+    testobj = (mps_addr_t)p_word;
+    mps_arena_release(arena);
+  }
+
+  /* Construct a pointer to roughly halfway inside the object */
+  in = (mps_addr_t)((char *)testobj + (N_SLOT_TESTOBJ/2) * sizeof(mps_word_t));
+
+  /* Ensure that this is an interior pointer, and not the base pointer,
+     since we want to make sure we are testing with a true interior pointer and not
+     one that also happens to be the base pointer. This Insist is intended to protect
+     against the testbench losing its ability to test "true" interior pointers (i.e. ones
+     which don't match the base pointer) if the test object sizes were changed to be very
+     small. Note that we don't currently consider the "limit" of the object as a corner case
+     (so we don't Insist(in != limit) ) but we do consider limit+1, i.e. the pointer to the
+     next object to be a corner case. This test could be updated to consider in == limit as a
+     corner case. */
+  Insist(in > testobj);
+
+  /* Do Test */
+  res = mps_addr_object(&out, arena, in);
+  Insist(out == testobj);
+  Insist(res == MPS_RES_OK);
+  printf("Interior pointer input: passed\n");
+
+
+  /* TEST 2: Test using the base pointer itself as an input*/
+
+  in = testobj;
+
+  /* Do Test */
+  res = mps_addr_object(&out, arena, in);
+  Insist(out == testobj);
+  Insist(res == MPS_RES_OK);
+  printf("Base pointer input: passed\n");
+
+
+
+   /* TEST 3: Test using a pointer one-off-the-end of the object*/
+
+  in =  (mps_addr_t)((char *)testobj + (N_SLOT_TESTOBJ + 2) * sizeof(mps_word_t));
+
+  /* Do Test */
+  res = mps_addr_object(&out, arena, in);
+  Insist(res == MPS_RES_FAIL);
+  printf("Pointer to next object input: passed\n");
+
+
+  /* Clean up from above tests */
+  mps_root_destroy(testobj_root);
+  mps_ap_destroy(obj_ap);
+  mps_pool_destroy(amcz_pool);
+  mps_fmt_destroy(obj_fmt);
+
+
+  /* TEST 4: Test using a pointer in unmanaged memory */
+
+  /* Use malloc to allocate non-mps-managed memory on the heap */
+  in = malloc(sizeof(mps_word_t));
+  Insist(NULL != in);
+
+  /* Do the test */
+  res = mps_addr_object(&out, arena, in);
+
+  /* Expect MPS to fail to find a base pointer for addresses not in managed memory */
+  Insist(res == MPS_RES_FAIL);
+  printf("Pointer to unmanaged memory input: passed\n");
+
+  /* clean up from this test */
+  if (NULL != in)
+    free(in);
+
+
+  /* TEST 5: Test using a pointer in a pool which currently doesn't implement mps_addr_object */
+
+  /* Create mvff pool for which mps_addr_object is not implemented */
+  die(mps_pool_create_k(&mvff_pool, arena, mps_class_mvff(), mps_args_none), "mps_pool_create_k mvff");
+
+  /* allocate an object (just some memory) in this pool */
+  die(mps_alloc(&in, mvff_pool, sizeof(mps_word_t)), "mps_alloc");
+
+  /* Do the test */
+  res = mps_addr_object(&out, arena, in);
+
+  Insist(res == MPS_RES_UNIMPL);
+  printf("Pointer to object in pool where mps_addr_object not implemented: passed\n");
+
+
+  /* If more tests are added here, briefly describe them above under "INTRO TO TESTS" comment */
+
+  /* Final clean up */
+  mps_free(mvff_pool, in, sizeof(mps_word_t));
+  mps_pool_destroy(mvff_pool);
+  mps_arena_destroy(arena);
+}
+
+int main(int argc, char *argv[])
+{
+  testlib_init(argc, argv);
+
+  test_main();
+
+  printf("%s: Conculsion, failed to find any defects.\n", argv[0]);
+
+  return 0;
+}
+
+/* C. COPYRIGHT AND LICENSE
+ *
+ * Copyright (C) 2022-2023 Ravenbrook Limited <https://www.ravenbrook.com/>.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */

code/arena.c

@@ -1364,6 +1364,22 @@ Bool ArenaHasAddr(Arena arena, Addr addr)
   return TractOfAddr(&tract, arena, addr);
 }
 
+/* ArenaAddrObject -- return base pointer of managed object */
+Res ArenaAddrObject(Addr *pReturn, Arena arena, Addr addr)
+{
+  Tract tract;
+
+  AVER(pReturn != NULL);
+  AVERT(Arena, arena);
+
+  if (!TractOfAddr(&tract, arena, addr)) {
+    /* address does not belong to the arena */
+    return ResFAIL;
+  }
+
+  return PoolAddrObject(pReturn, TractPool(tract), addr);
+}
+
 
 /* C. COPYRIGHT AND LICENSE
  *

code/comm.gmk

@@ -253,6 +253,7 @@ LIB_TARGETS=mps.a mpsplan.a
 
 TEST_TARGETS=\
     abqtest \
+    addrobj \
     airtest \
     amcss \
     amcsshe \
@@ -446,6 +447,9 @@ ifdef VARIETY
 $(PFM)/$(VARIETY)/abqtest: $(PFM)/$(VARIETY)/abqtest.o \
 	$(TESTLIBOBJ) $(PFM)/$(VARIETY)/mps.a
 
+$(PFM)/$(VARIETY)/addrobj: $(PFM)/$(VARIETY)/addrobj.o \
+	$(FMTDYTSTOBJ) $(TESTLIBOBJ) $(PFM)/$(VARIETY)/mps.a
+
 $(PFM)/$(VARIETY)/airtest: $(PFM)/$(VARIETY)/airtest.o \
 	$(FMTSCMOBJ) $(TESTLIBOBJ) $(PFM)/$(VARIETY)/mps.a
 

code/commpost.nmk

@@ -177,6 +177,9 @@ $(PFM)\cool\mps.lib: $(MPMOBJ)
 $(PFM)\$(VARIETY)\abqtest.exe: $(PFM)\$(VARIETY)\abqtest.obj \
 	$(PFM)\$(VARIETY)\mps.lib $(TESTLIBOBJ)
 
+$(PFM)\$(VARIETY)\addrobj.exe: $(PFM)\$(VARIETY)\addrobj.obj \
+	$(PFM)\$(VARIETY)\mps.lib $(FMTTESTOBJ) $(TESTLIBOBJ)
+
 $(PFM)\$(VARIETY)\airtest.exe: $(PFM)\$(VARIETY)\airtest.obj \
 	$(PFM)\$(VARIETY)\mps.lib $(FMTSCHEMEOBJ) $(TESTLIBOBJ)
 

code/commpre.nmk

@@ -59,6 +59,7 @@ LIB_TARGETS=mps.lib
 
 TEST_TARGETS=\
     abqtest.exe \
+    addrobj.exe \
     airtest.exe \
     amcss.exe \
     amcsshe.exe \

code/mpm.h

@@ -236,6 +236,7 @@ extern Res PoolTraceBegin(Pool pool, Trace trace);
 extern void PoolFreeWalk(Pool pool, FreeBlockVisitor f, void *p);
 extern Size PoolTotalSize(Pool pool);
 extern Size PoolFreeSize(Pool pool);
+extern Res PoolAddrObject(Addr *pReturn, Pool pool, Addr addr);
 
 extern Res PoolAbsInit(Pool pool, Arena arena, PoolClass klass, ArgList arg);
 extern void PoolAbsFinish(Inst inst);
@@ -267,6 +268,7 @@ extern void PoolTrivFreeWalk(Pool pool, FreeBlockVisitor f, void *p);
 extern PoolDebugMixin PoolNoDebugMixin(Pool pool);
 extern BufferClass PoolNoBufferClass(void);
 extern Size PoolNoSize(Pool pool);
+extern Res PoolTrivAddrObject(Addr *pReturn, Pool pool, Addr addr);
 
 /* See .critical.macros. */
 #define PoolFreeMacro(pool, old, size) Method(Pool, pool, free)(pool, old, size)
@@ -536,6 +538,7 @@ extern Res ArenaStartCollect(Globals globals, TraceStartWhy why);
 extern Res ArenaCollect(Globals globals, TraceStartWhy why);
 extern Bool ArenaBusy(Arena arena);
 extern Bool ArenaHasAddr(Arena arena, Addr addr);
+extern Res ArenaAddrObject(Addr *pReturn, Arena arena, Addr addr);
 extern void ArenaChunkInsert(Arena arena, Chunk chunk);
 extern void ArenaChunkRemoved(Arena arena, Chunk chunk);
 extern void ArenaAccumulateTime(Arena arena, Clock start, Clock now);

code/mpmst.h

@@ -60,6 +60,7 @@ typedef struct mps_pool_class_s {
   PoolRampEndMethod rampEnd;    /* end a ramp pattern */
   PoolFramePushMethod framePush; /* push an allocation frame */
   PoolFramePopMethod framePop;  /* pop an allocation frame */
+  PoolAddrObjectMethod addrObject; /* return object's base pointer */
   PoolFreeWalkMethod freewalk;  /* walk over free blocks */
   PoolBufferClassMethod bufferClass; /* default BufferClass of pool */
   PoolDebugMixinMethod debugMixin; /* find the debug mixin, if any */

code/mpmtypes.h

@@ -214,6 +214,7 @@ typedef Res (*PoolFramePushMethod)(AllocFrame *frameReturn,
                                    Pool pool, Buffer buf);
 typedef Res (*PoolFramePopMethod)(Pool pool, Buffer buf,
                                   AllocFrame frame);
+typedef Res (*PoolAddrObjectMethod)(Addr *pReturn, Pool pool, Addr addr);
 typedef void (*PoolFreeWalkMethod)(Pool pool, FreeBlockVisitor f, void *p);
 typedef BufferClass (*PoolBufferClassMethod)(void);
 typedef PoolDebugMixin (*PoolDebugMixinMethod)(Pool pool);

code/mps.h

@@ -845,6 +845,8 @@ extern mps_res_t _mps_fix2(mps_ss_t, mps_addr_t *);
    (ss)->_ufs = _mps_ufs; \
   MPS_END
 
+/* Misc interface */
+extern mps_res_t mps_addr_object(mps_addr_t *p_o, mps_arena_t arena, mps_addr_t addr);
 
 #endif /* mps_h */