FreeChainXenon/binutils-gdb
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gdb: Fix numerical field extraction for target description "flags"

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The "val_print_type_code_flags ()" function is responsible for
extraction of fields for "flags" data type.  These data types are
used when describing a custom register type in a target description
XML.  The logic used for the extraction though is not sound:

    unsigned field_len = TYPE_FIELD_BITSIZE (type, field);
    ULONGEST field_val
      = val >> (TYPE_FIELD_BITPOS (type, field) - field_len + 1);

TYPE_FIELD_BITSIZE: The bit length of the field to be extracted.
TYPE_FIELD_BITPOS:  The starting position of the field; 0 is LSB.
val:                The register value.

Imagine you have a field that starts at position 1 and its length
is 4 bits.  According to the third line of the code snippet the
shifting right would become "val >> -2", or "val >> 0xfff...fe"
to be precise.  That will result in a "field_val" of 0.

The correct extraction should be:

    ULONGEST field_val = val >> TYPE_FIELD_BITPOS (type, field);

The rest of the algorithm that masks out the higher bits is OK.

Co-Authored-By: Simon Marchi <simon.marchi@efficios.com>
This commit is contained in:
Shahab Vahedi 2021-07-16 16:49:15 +02:00
parent 0264bf6fe3
commit c9bd98593b
1 changed files with 34 additions and 2 deletions
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36
gdb/valprint.c
View file

@ -43,6 +43,8 @@
#include "c-lang.h"
#include "cp-abi.h"
#include "inferior.h"
#include "gdbsupport/selftest.h"
#include "selftest-arch.h"
/* Maximum number of wchars returned from wchar_iterate. */
#define MAX_WCHARS 4
@ -1221,8 +1223,7 @@ val_print_type_code_flags (struct type *type, struct value *original_value,
else
{
unsigned field_len = TYPE_FIELD_BITSIZE (type, field);
ULONGEST field_val
= val >> (TYPE_FIELD_BITPOS (type, field) - field_len + 1);
ULONGEST field_val = val >> TYPE_FIELD_BITPOS (type, field);
if (field_len < sizeof (ULONGEST) * TARGET_CHAR_BIT)
field_val &= ((ULONGEST) 1 << field_len) - 1;
@ -3137,10 +3138,41 @@ make_value_print_options_def_group (value_print_options *opts)
return {{value_print_option_defs}, opts};
}
#if GDB_SELF_TEST
/* Test printing of TYPE_CODE_FLAGS values. */
static void
test_print_flags (gdbarch *arch)
{
type *flags_type = arch_flags_type (arch, "test_type", 32);
type *field_type = builtin_type (arch)->builtin_uint32;
/* Value: 1010 1010
Fields: CCCB BAAA */
append_flags_type_field (flags_type, 0, 3, field_type, "A");
append_flags_type_field (flags_type, 3, 2, field_type, "B");
append_flags_type_field (flags_type, 5, 3, field_type, "C");
value *val = allocate_value (flags_type);
gdb_byte *contents = value_contents_writeable (val);
store_unsigned_integer (contents, 4, gdbarch_byte_order (arch), 0xaa);
string_file out;
val_print_type_code_flags (flags_type, val, 0, &out);
SELF_CHECK (out.string () == "[ A=2 B=1 C=5 ]");
}
#endif
void _initialize_valprint ();
void
_initialize_valprint ()
{
#if GDB_SELF_TEST
selftests::register_test_foreach_arch ("print-flags", test_print_flags);
#endif
cmd_list_element *cmd;
cmd_list_element *set_print_cmd