gdb/fortran: Support negative array stride in one limited case

This commit adds support for negative Fortran array strides in one
limited case, that is the case of a single element array with a
negative array stride.

The changes in this commit will be required in order for more general
negative array stride support to work correctly, however, right now
other problems in GDB prevent negative array strides from working in
the general case.

The reason negative array strides don't currently work in the general
case is that when dealing with such arrays, the base address for the
objects data is actually the highest addressed element, subsequent
elements are then accessed with a negative offset from that address,
and GDB is not currently happy with this configuration.

The changes here can be summarised as, stop treating signed values as
unsigned, specifically, the array stride, and offsets calculated using
the array stride.

This issue was identified on the mailing list by Sergio:

  https://sourceware.org/ml/gdb-patches/2020-01/msg00360.html

The test for this issue is a new one written by me as the copyright
status of the original test is currently unknown.

gdb/ChangeLog:

	* gdbtypes.c (create_array_type_with_stride): Handle negative
	array strides.
	* valarith.c (value_subscripted_rvalue): Likewise.

gdb/testsuite/ChangeLog:

	* gdb.fortran/derived-type-striding.exp: Add a new test.
	* gdb.fortran/derived-type-striding.f90: Add pointer variable for
	new test.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 879a17a653c3257de98c54c4aef6a6158f012e2a..cb3e1854ac2d1afc7de6ad2fc01f048b7e56b184 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-25  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+       * gdbtypes.c (create_array_type_with_stride): Handle negative
+       array strides.
+       * valarith.c (value_subscripted_rvalue): Likewise.
+
 2020-02-25  Luis Machado  <luis.machado@linaro.org>
 
        * aarch64-tdep.c (aarch64_vnv_type): Fix comment typo.

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 85758930491f92a6eaac8dc7a80e4eefd38d3afd..ef110b30445f82cc464240a2ed55e3ce08500729 100644 (file)
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1223,7 +1223,7 @@ create_array_type_with_stride (struct type *result_type,
          && !type_not_allocated (result_type)))
     {
       LONGEST low_bound, high_bound;
-      unsigned int stride;
+      int stride;
 
       /* If the array itself doesn't provide a stride value then take
         whatever stride the range provides.  Don't update BIT_STRIDE as
@@ -1241,9 +1241,18 @@ create_array_type_with_stride (struct type *result_type,
         In such cases, the array length should be zero.  */
       if (high_bound < low_bound)
        TYPE_LENGTH (result_type) = 0;
-      else if (stride > 0)
-       TYPE_LENGTH (result_type) =
-         (stride * (high_bound - low_bound + 1) + 7) / 8;
+      else if (stride != 0)
+       {
+         /* Ensure that the type length is always positive, even in the
+            case where (for example in Fortran) we have a negative
+            stride.  It is possible to have a single element array with a
+            negative stride in Fortran (this doesn't mean anything
+            special, it's still just a single element array) so do
+            consider that case when touching this code.  */
+         LONGEST element_count = abs (high_bound - low_bound + 1);
+         TYPE_LENGTH (result_type)
+           = ((abs (stride) * element_count) + 7) / 8;
+       }
       else
        TYPE_LENGTH (result_type) =
          TYPE_LENGTH (element_type) * (high_bound - low_bound + 1);

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index ccbb5be8fc1c078659dd3d10870abef1c2ab5d6a..720febb65cc35b1e67106d6136adbb3406a87f36 100644 (file)
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-25  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+       * gdb.fortran/derived-type-striding.exp: Add a new test.
+       * gdb.fortran/derived-type-striding.f90: Add pointer variable for
+       new test.
+
 2020-02-25  Andrew Burgess  <andrew.burgess@embecosm.com>
 
        * gdb.base/cached-source-file.exp: Avoid source file paths in test

diff --git a/gdb/testsuite/gdb.fortran/derived-type-striding.exp b/gdb/testsuite/gdb.fortran/derived-type-striding.exp
index 094843ca8b18413676523a4d8a63b0f8ea94be13..639dc4c95289ec6ba239f547c21568c17efa30fa 100644 (file)
--- a/gdb/testsuite/gdb.fortran/derived-type-striding.exp
+++ b/gdb/testsuite/gdb.fortran/derived-type-striding.exp
@@ -41,3 +41,5 @@ gdb_test "p point_dimension" "= \\\(2, 2, 2, 2, 2, 2, 2, 2, 2\\\)"
 # Test mixed type derived type.
 if { $gcc_with_broken_stride } { setup_kfail *-*-* gcc/92775 }
 gdb_test "p point_mixed_dimension" "= \\\(3, 3, 3, 3\\\)"
+
+gdb_test "p cloud_slice" " = \\\(\\\( x = 1, y = 2, z = 3 \\\)\\\)"

diff --git a/gdb/testsuite/gdb.fortran/derived-type-striding.f90 b/gdb/testsuite/gdb.fortran/derived-type-striding.f90
index 26829f51dc0a09cda48f59bcdb48d8b8e453277f..fb537579faadb62cd61eb5921cfd162428abac60 100644 (file)
--- a/gdb/testsuite/gdb.fortran/derived-type-striding.f90
+++ b/gdb/testsuite/gdb.fortran/derived-type-striding.f90
@@ -28,9 +28,11 @@ program derived_type_member_stride
     type(mixed_cartesian), dimension(10), target :: mixed_cloud
     integer(kind=8), dimension(:), pointer :: point_dimension => null()
     integer(kind=8), dimension(:), pointer :: point_mixed_dimension => null()
+    type(cartesian), dimension(:), pointer :: cloud_slice => null()
     cloud(:)%x = 1
     cloud(:)%y = 2
     cloud(:)%z = 3
+    cloud_slice => cloud(3:2:-2)
     point_dimension => cloud(1:9)%y
     mixed_cloud(:)%x = 1
     mixed_cloud(:)%y = 2

diff --git a/gdb/valarith.c b/gdb/valarith.c
index 79b148602bb54945756e84afaec90c0c1223e521..be0e0731bee13e0a9910d769ac0ebec67a9c00d1 100644 (file)
--- a/gdb/valarith.c
+++ b/gdb/valarith.c
@@ -187,7 +187,7 @@ value_subscripted_rvalue (struct value *array, LONGEST index, LONGEST lowerbound
 {
   struct type *array_type = check_typedef (value_type (array));
   struct type *elt_type = check_typedef (TYPE_TARGET_TYPE (array_type));
-  ULONGEST elt_size = type_length_units (elt_type);
+  LONGEST elt_size = type_length_units (elt_type);
 
   /* Fetch the bit stride and convert it to a byte stride, assuming 8 bits
      in a byte.  */
@@ -199,7 +199,7 @@ value_subscripted_rvalue (struct value *array, LONGEST index, LONGEST lowerbound
       elt_size = stride / (unit_size * 8);
     }
 
-  ULONGEST elt_offs = elt_size * (index - lowerbound);
+  LONGEST elt_offs = elt_size * (index - lowerbound);
 
   if (index < lowerbound
       || (!TYPE_ARRAY_UPPER_BOUND_IS_UNDEFINED (array_type)