commit d5d1163eff2415a01895f1cff8bbee32b3f0ab66

Author: Andreas Arnez <arnez@linux.vnet.ibm.com>

Date:   Tue Jun 13 15:20:26 2017 +0200

    write_pieced_value: Fix size capping logic

    A field f in a structure composed of DWARF pieces may be located in

    multiple pieces, where the first and last of those may contain bits from

    other fields as well.  So when writing to f, the beginning of the first

    and the end of the last of those pieces may have to be skipped.  But the

    logic in write_pieced_value for handling one of those pieces is flawed

    when the first and last piece are the same, i.e., f is contained in a

    single piece:

      < - - - - - - - - - piece_size - - - - - - - - - ->

      +-------------------------------------------------+

      | skipped_bits |   f_bits   | / / / / / / / / / / |

      +-------------------------------------------------+

    The current logic determines the size of the sub-piece to operate on by

    limiting the piece size to the bit size of f and then subtracting the

    skipped bits:

      min (piece_size, f_bits) - skipped_bits

    Instead of:

      min (piece_size - skipped_bits, f_bits)

    So the resulting sub-piece size is corrupted, leading to wrong handling of

    this piece in write_pieced_value.

    Note that the same bug was already found in read_pieced_value and fixed

    there (but not in write_pieced_value), see PR 15391.

    This patch swaps the calculations, bringing them into the same (correct)

    order as in read_pieced_value.

    gdb/ChangeLog:

            * dwarf2loc.c (write_pieced_value): Fix order of calculations for

            size capping.

    gdb/testsuite/ChangeLog:

            * gdb.dwarf2/var-pieces.exp: Add test case for modifying a

            variable at nonzero offset.

### a/gdb/ChangeLog

### b/gdb/ChangeLog

## -1,3 +1,8 @@

+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>

+

+	* dwarf2loc.c (write_pieced_value): Fix order of calculations for

+	size capping.

+

 2017-06-13  Yao Qi  <yao.qi@linaro.org>

 	* mips-linux-nat.c: Move include features/mips*-linux.c to

--- a/gdb/dwarf2loc.c

+++ b/gdb/dwarf2loc.c

@@ -1964,8 +1964,6 @@ write_pieced_value (struct value *to, struct value *from)

 	  bits_to_skip -= this_size_bits;

 	  continue;

 	}

-      if (this_size_bits > type_len - offset)

-	this_size_bits = type_len - offset;

       if (bits_to_skip > 0)

 	{

 	  dest_offset_bits = bits_to_skip;

@@ -1978,6 +1976,8 @@ write_pieced_value (struct value *to, struct value *from)

 	  dest_offset_bits = 0;

 	  source_offset_bits = offset;

 	}

+      if (this_size_bits > type_len - offset)

+	this_size_bits = type_len - offset;

       this_size = (this_size_bits + source_offset_bits % 8 + 7) / 8;

       source_offset = source_offset_bits / 8;

### a/gdb/testsuite/ChangeLog

### b/gdb/testsuite/ChangeLog

## -1,5 +1,10 @@

 2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>

+	* gdb.dwarf2/var-pieces.exp: Add test case for modifying a

+	variable at nonzero offset.

+

+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>

+

 	* gdb.dwarf2/var-access.c: New file.

 	* gdb.dwarf2/var-access.exp: New test.

 	* lib/gdb-utils.exp (string_to_regexp): Quote braces as well.

--- a/gdb/testsuite/gdb.dwarf2/var-access.exp

+++ b/gdb/testsuite/gdb.dwarf2/var-access.exp

@@ -178,6 +178,11 @@ gdb_test "print/d s1" " = \\{a = 63, b = 3, c = 0, d = 1\\}" \

     "verify s1.a"

 gdb_test "print/d a" " = \\{0, 1, 63, 3, 4, 5, 6, 7\\}" \

     "verify s1.a through a"

+gdb_test_no_output "set var s1.b = 42"

+gdb_test "print/d s1" " = \\{a = 63, b = 42, c = 0, d = 1\\}" \

+    "verify s1.b"

+gdb_test "print/d a" " = \\{0, 1, 63, 42, 4, 5, 6, 7\\}" \

+    "verify s1.b through a"

 # Byte-aligned register- and memory pieces.

 gdb_test_no_output "set var \$[lindex $regname 0] = 81" \