[flang][runtime] Validate pointer DEALLOCATE (#78612)

The standard requires a compiler to diagnose an incorrect use of a
pointer in a DEALLOCATE statement. The pointer must be associated with
an entire object that was allocated as a pointer (not allocatable) by an
ALLOCATE statement.

Implement by appending a validation footer to pointer allocations. This
is an extra allocated word that encodes the base address of the
allocation. If it is not found after the data payload when the pointer
is deallocated, signal an error. There is a chance of a false positive
result, but that should be vanishingly unlikely.

This change requires all pointer allocations (not allocatables) to take
place in the runtime in PointerAllocate(), which might be slower in
cases that could otherwise be handled with a native memory allocation
operation. I believe that memory allocation of pointers is less common
than with allocatables, which are not affected. If this turns out to
become a performance problem, we can inline the creation and
initialization of the footer word.

Fixes #78391.

Author: klausler

flang/include/flang/Runtime/descriptor.h

@@ -375,6 +375,7 @@ class Descriptor {
   // allocation.  Does not allocate automatic components or
   // perform default component initialization.
   RT_API_ATTRS int Allocate();
+  RT_API_ATTRS void SetByteStrides();
 
   // Deallocates storage; does not call FINAL subroutines or
   // deallocate allocatable/automatic components.

flang/include/flang/Runtime/magic-numbers.h

@@ -63,6 +63,11 @@ same allocatable.
 #endif
 #define FORTRAN_RUNTIME_STAT_MOVE_ALLOC_SAME_ALLOCATABLE 109
 
+#if 0
+Additional status code for a bad pointer DEALLOCATE.
+#endif
+#define FORTRAN_RUNTIME_STAT_BAD_POINTER_DEALLOCATION 110
+
 #if 0
 ieee_class_type values
 The sequence is that of F18 Clause 17.2p3, but nothing depends on that.

flang/lib/Lower/Allocatable.cpp

@@ -454,7 +454,9 @@ class AllocateStmtHelper {
                            const fir::MutableBoxValue &box) {
     if (!box.isDerived() && !errorManager.hasStatSpec() &&
         !alloc.type.IsPolymorphic() && !alloc.hasCoarraySpec() &&
-        !useAllocateRuntime) {
+        !useAllocateRuntime && !box.isPointer()) {
+      // Pointers must use PointerAllocate so that their deallocations
+      // can be validated.
       genInlinedAllocation(alloc, box);
       return;
     }

flang/runtime/descriptor.cpp

@@ -152,7 +152,13 @@ RT_API_ATTRS std::size_t Descriptor::Elements() const {
 }
 
 RT_API_ATTRS int Descriptor::Allocate() {
-  std::size_t byteSize{Elements() * ElementBytes()};
+  std::size_t elementBytes{ElementBytes()};
+  if (static_cast<std::int64_t>(elementBytes) < 0) {
+    // F'2023 7.4.4.2 p5: "If the character length parameter value evaluates
+    // to a negative value, the length of character entities declared is zero."
+    elementBytes = raw_.elem_len = 0;
+  }
+  std::size_t byteSize{Elements() * elementBytes};
   // Zero size allocation is possible in Fortran and the resulting
   // descriptor must be allocated/associated. Since std::malloc(0)
   // result is implementation defined, always allocate at least one byte.
@@ -162,6 +168,11 @@ RT_API_ATTRS int Descriptor::Allocate() {
   }
   // TODO: image synchronization
   raw_.base_addr = p;
+  SetByteStrides();
+  return 0;
+}
+
+RT_API_ATTRS void Descriptor::SetByteStrides() {
   if (int dims{rank()}) {
     std::size_t stride{ElementBytes()};
     for (int j{0}; j < dims; ++j) {
@@ -170,7 +181,6 @@ RT_API_ATTRS int Descriptor::Allocate() {
       stride *= dimension.Extent();
     }
   }
-  return 0;
 }
 
 RT_API_ATTRS int Descriptor::Destroy(

flang/runtime/pointer.cpp

@@ -129,17 +129,38 @@ int RTDEF(PointerAllocate)(Descriptor &pointer, bool hasStat,
   if (!pointer.IsPointer()) {
     return ReturnError(terminator, StatInvalidDescriptor, errMsg, hasStat);
   }
-  int stat{ReturnError(terminator, pointer.Allocate(), errMsg, hasStat)};
-  if (stat == StatOk) {
-    if (const DescriptorAddendum * addendum{pointer.Addendum()}) {
-      if (const auto *derived{addendum->derivedType()}) {
-        if (!derived->noInitializationNeeded()) {
-          stat = Initialize(pointer, *derived, terminator, hasStat, errMsg);
-        }
+  std::size_t elementBytes{pointer.ElementBytes()};
+  if (static_cast<std::int64_t>(elementBytes) < 0) {
+    // F'2023 7.4.4.2 p5: "If the character length parameter value evaluates
+    // to a negative value, the length of character entities declared is zero."
+    elementBytes = pointer.raw().elem_len = 0;
+  }
+  std::size_t byteSize{pointer.Elements() * elementBytes};
+  // Add space for a footer to validate during DEALLOCATE.
+  constexpr std::size_t align{sizeof(std::uintptr_t)};
+  byteSize = ((byteSize + align - 1) / align) * align;
+  std::size_t total{byteSize + sizeof(std::uintptr_t)};
+  void *p{std::malloc(total)};
+  if (!p) {
+    return ReturnError(terminator, CFI_ERROR_MEM_ALLOCATION, errMsg, hasStat);
+  }
+  pointer.set_base_addr(p);
+  pointer.SetByteStrides();
+  // Fill the footer word with the XOR of the ones' complement of
+  // the base address, which is a value that would be highly unlikely
+  // to appear accidentally at the right spot.
+  std::uintptr_t *footer{
+      reinterpret_cast<std::uintptr_t *>(static_cast<char *>(p) + byteSize)};
+  *footer = ~reinterpret_cast<std::uintptr_t>(p);
+  int stat{StatOk};
+  if (const DescriptorAddendum * addendum{pointer.Addendum()}) {
+    if (const auto *derived{addendum->derivedType()}) {
+      if (!derived->noInitializationNeeded()) {
+        stat = Initialize(pointer, *derived, terminator, hasStat, errMsg);
       }
     }
   }
-  return stat;
+  return ReturnError(terminator, stat, errMsg, hasStat);
 }
 
 int RTDEF(PointerAllocateSource)(Descriptor &pointer, const Descriptor &source,
@@ -163,6 +184,18 @@ int RTDEF(PointerDeallocate)(Descriptor &pointer, bool hasStat,
   if (!pointer.IsAllocated()) {
     return ReturnError(terminator, StatBaseNull, errMsg, hasStat);
   }
+  // Validate the footer.  This should fail if the pointer doesn't
+  // span the entire object, or the object was not allocated as a
+  // pointer.
+  std::size_t byteSize{pointer.Elements() * pointer.ElementBytes()};
+  constexpr std::size_t align{sizeof(std::uintptr_t)};
+  byteSize = ((byteSize + align - 1) / align) * align;
+  void *p{pointer.raw().base_addr};
+  std::uintptr_t *footer{
+      reinterpret_cast<std::uintptr_t *>(static_cast<char *>(p) + byteSize)};
+  if (*footer != ~reinterpret_cast<std::uintptr_t>(p)) {
+    return ReturnError(terminator, StatBadPointerDeallocation, errMsg, hasStat);
+  }
   return ReturnError(terminator,
       pointer.Destroy(/*finalize=*/true, /*destroyPointers=*/true, &terminator),
       errMsg, hasStat);

flang/runtime/stat.cpp

@@ -66,6 +66,10 @@ RT_API_ATTRS const char *StatErrorString(int stat) {
   case StatMoveAllocSameAllocatable:
     return "MOVE_ALLOC passed the same address as to and from";
 
+  case StatBadPointerDeallocation:
+    return "DEALLOCATE of a pointer that is not the whole content of a pointer "
+           "ALLOCATE";
+
   default:
     return nullptr;
   }

flang/runtime/stat.h

@@ -51,6 +51,7 @@ enum Stat {
   StatValueTooShort = FORTRAN_RUNTIME_STAT_VALUE_TOO_SHORT,
   StatMoveAllocSameAllocatable =
       FORTRAN_RUNTIME_STAT_MOVE_ALLOC_SAME_ALLOCATABLE,
+  StatBadPointerDeallocation = FORTRAN_RUNTIME_STAT_BAD_POINTER_DEALLOCATION,
 };
 
 RT_API_ATTRS const char *StatErrorString(int);

flang/test/Lower/Intrinsics/c_loc.f90

@@ -177,20 +177,37 @@ subroutine c_loc_arraysection()
 ! CHECK:         %[[VAL_2:.*]] = fir.zero_bits !fir.ptr<i32>
 ! CHECK:         fir.store %[[VAL_2]] to %[[VAL_1]] : !fir.ref<!fir.ptr<i32>>
 ! CHECK:         %[[VAL_3:.*]] = fir.alloca !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}> {bindc_name = "ptr", uniq_name = "_QFc_loc_non_save_pointer_scalarEptr"}
-! CHECK:         %[[VAL_4:.*]] = fir.allocmem i32 {fir.must_be_heap = true, uniq_name = "_QFc_loc_non_save_pointer_scalarEi.alloc"}
-! CHECK:         %[[VAL_5:.*]] = fir.convert %[[VAL_4]] : (!fir.heap<i32>) -> !fir.ptr<i32>
-! CHECK:         fir.store %[[VAL_5]] to %[[VAL_1]] : !fir.ref<!fir.ptr<i32>>
-! CHECK:         %[[VAL_6:.*]] = arith.constant 10 : i32
-! CHECK:         %[[VAL_7:.*]] = fir.load %[[VAL_1]] : !fir.ref<!fir.ptr<i32>>
-! CHECK:         fir.store %[[VAL_6]] to %[[VAL_7]] : !fir.ptr<i32>
-! CHECK:         %[[VAL_8:.*]] = fir.load %[[VAL_1]] : !fir.ref<!fir.ptr<i32>>
-! CHECK:         %[[VAL_9:.*]] = fir.embox %[[VAL_8]] : (!fir.ptr<i32>) -> !fir.box<i32>
-! CHECK:         %[[VAL_10:.*]] = fir.alloca !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>
-! CHECK-DAG:         %[[VAL_11:.*]] = fir.box_addr %[[VAL_9]] : (!fir.box<i32>) -> !fir.ref<i32>
-! CHECK-DAG:         %[[VAL_12:.*]] = fir.convert %[[VAL_11]] : (!fir.ref<i32>) -> i64
-! CHECK-DAG:         %[[VAL_13:.*]] = fir.field_index __address, !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>
-! CHECK-DAG:         %[[VAL_14:.*]] = fir.coordinate_of %[[VAL_10]], %[[VAL_13]] : (!fir.ref<!fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>>, !fir.field) -> !fir.ref<i64>
-! CHECK:         fir.store %[[VAL_12]] to %[[VAL_14]] : !fir.ref<i64>
+! CHECK:         %[[VAL_false:.*]] = arith.constant false
+! CHECK:         %[[VAL_4:.*]] = fir.absent !fir.box<none>
+! CHECK:         %[[VAL_5:.*]] = fir.address_of(@{{.*}}) : !fir.ref<!fir.char<1,{{.*}}>>
+! CHECK:         %[[C_LN:.*]] = arith.constant {{.*}} : i32
+! CHECK:         %[[VAL_6:.*]] = fir.zero_bits !fir.ptr<i32>
+! CHECK:         %[[VAL_7:.*]] = fir.embox %[[VAL_6:.*]] : (!fir.ptr<i32>) -> !fir.box<!fir.ptr<i32>>
+! CHECK:         fir.store %[[VAL_7:.*]] to %[[VAL_0:.*]] : !fir.ref<!fir.box<!fir.ptr<i32>>>
+! CHECK:         %[[VAL_8:.*]] = fir.convert %[[VAL_0:.*]] : (!fir.ref<!fir.box<!fir.ptr<i32>>>) -> !fir.ref<!fir.box<none>>
+! CHECK:         %[[VAL_9:.*]] = fir.convert %[[VAL_5:.*]] : (!fir.ref<!fir.char<1,{{.*}}>>) -> !fir.ref<i8>
+! CHECK:         %[[VAL_10:.*]] = fir.call @_FortranAPointerAllocate(%[[VAL_8:.*]], %[[VAL_false:.*]], %[[VAL_4:.*]], %[[VAL_9:.*]], %[[C_LN:.*]]) fastmath<contract> : (!fir.ref<!fir.box<none>>, i1, !fir.box<none>, !fir.ref<i8>, i32) -> i32
+! CHECK:         %[[VAL_11:.*]] = fir.load %[[VAL_0:.*]] : !fir.ref<!fir.box<!fir.ptr<i32>>>
+! CHECK:         %[[VAL_12:.*]] = fir.box_addr %[[VAL_11:.*]] : (!fir.box<!fir.ptr<i32>>) -> !fir.ptr<i32>
+! CHECK:         fir.store %[[VAL_12:.*]] to %[[VAL_1:.*]] : !fir.ref<!fir.ptr<i32>>
+! CHECK:         %[[C_10:.*]] = arith.constant 10 : i32
+! CHECK:         %[[VAL_13:.*]] = fir.load %[[VAL_1:.*]] : !fir.ref<!fir.ptr<i32>>
+! CHECK:         fir.store %[[C_10]] to %[[VAL_13:.*]] : !fir.ptr<i32>
+! CHECK:         %[[VAL_14:.*]] = fir.load %[[VAL_1:.*]] : !fir.ref<!fir.ptr<i32>>
+! CHECK:         %[[VAL_15:.*]] = fir.embox %[[VAL_14:.*]] : (!fir.ptr<i32>) -> !fir.box<i32>
+! CHECK:         %[[VAL_16:.*]] = fir.alloca !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>
+! CHECK:         %[[VAL_17:.*]] = fir.field_index __address, !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>
+! CHECK:         %[[VAL_18:.*]] = fir.coordinate_of %[[VAL_16:.*]], %[[VAL_17:.*]] : (!fir.ref<!fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>>, !fir.field) -> !fir.ref<i64>
+! CHECK:         %[[VAL_19:.*]] = fir.box_addr %[[VAL_15:.*]] : (!fir.box<i32>) -> !fir.ref<i32>
+! CHECK:         %[[VAL_20:.*]] = fir.convert %[[VAL_19:.*]] : (!fir.ref<i32>) -> i64
+! CHECK:         fir.store %[[VAL_20:.*]] to %[[VAL_18:.*]] : !fir.ref<i64>
+! CHECK:         %[[VAL_21:.*]] = fir.field_index __address, !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>
+! CHECK:         %[[VAL_22:.*]] = fir.coordinate_of %[[VAL_16:.*]], %[[VAL_21:.*]] : (!fir.ref<!fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>>, !fir.field) -> !fir.ref<i64>
+! CHECK:         %[[VAL_23:.*]] = fir.field_index __address, !fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>
+! CHECK:         %[[VAL_24:.*]] = fir.coordinate_of %[[VAL_3:.*]], %[[VAL_23:.*]] : (!fir.ref<!fir.type<_QM__fortran_builtinsT__builtin_c_ptr{__address:i64}>>, !fir.field) -> !fir.ref<i64>
+! CHECK:         %[[VAL_25:.*]] = fir.load %[[VAL_22:.*]] : !fir.ref<i64>
+! CHECK:         fir.store %[[VAL_25:.*]] to %[[VAL_24:.*]] : !fir.ref<i64>
+! CHECK:         return
 ! CHECK:       }
 
 subroutine c_loc_non_save_pointer_scalar()