On 9/4/18 5:59 PM, Tom de Vries wrote:
> [ Adding Jason as addressee ]
>
> On 08/28/2018 08:20 PM, Omar Sandoval wrote:
>> On Fri, Aug 17, 2018 at 12:16:07AM -0700, Omar Sandoval wrote:
>>> On Thu, Aug 16, 2018 at 11:54:53PM -0700, Omar Sandoval wrote:
>>>> On Thu, Aug 16, 2018 at 10:27:48PM -0700, Andrew Pinski wrote:
>>>>> On Thu, Aug 16, 2018 at 9:29 PM Omar Sandoval <osan...@osandov.com> wrote:
>>>>>> Hi,
>>>>>>
>>>>>> This fixes the issue that it is impossible to distinguish a zero-length
>>>>>> array
>>>>>> type from a flexible array type given the DWARF produced by GCC (which I
>>>>>> reported here [1]). We do so by adding a DW_AT_count attribute with a
>>>>>> value of
>>>>>> zero only for zero-length arrays (this is what clang does in this case,
>>>>>> too).
>>>>>>
>>>>>> 1: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86985
>>>>>>
>>>>>> The reproducer from the PR now produces the expected output:
>>>>>>
>>>>>> $ ~/gcc-build/gcc/xgcc -B ~/gcc-build/gcc -g -c zero_length.c
>>>>>> $ ~/gcc-build/gcc/xgcc -B ~/gcc-build/gcc -g -c flexible.c
>>>>>> $ gdb -batch -ex 'ptype baz' zero_length.o
>>>>>> type = struct {
>>>>>> int foo;
>>>>>> int bar[0];
>>>>>> }
>>>>>> $ gdb -batch -ex 'ptype baz' flexible.o
>>>>>> type = struct {
>>>>>> int foo;
>>>>>> int bar[];
>>>>>> }
>>>>>>
>>>>>> This was bootstrapped and tested on x86_64-pc-linux-gnu.
>>>>>>
>>>>>> I don't have commit rights (first time contributor), so if this change
>>>>>> is okay
>>>>>> could it please be applied?
>>> [snip]
>>>
>>> Here's the patch with the is_c () helper instead.
>>>
>>> 2018-08-17 Omar Sandoval <osan...@osandov.com>
>>>
> I've added the PR number here.
>
>>> * dwarf2out.c (is_c): New.
>>> (add_subscript_info): Add DW_AT_count of 0 for C zero-length arrays.
>>>
>>> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
>>> index 5a74131d332..189f9bb381f 100644
>>> --- a/gcc/dwarf2out.c
>>> +++ b/gcc/dwarf2out.c
>>> @@ -3671,6 +3671,7 @@ static const char *get_AT_string (dw_die_ref, enum
>>> dwarf_attribute);
>>> static int get_AT_flag (dw_die_ref, enum dwarf_attribute);
>>> static unsigned get_AT_unsigned (dw_die_ref, enum dwarf_attribute);
>>> static inline dw_die_ref get_AT_ref (dw_die_ref, enum dwarf_attribute);
>>> +static bool is_c (void);
>>> static bool is_cxx (void);
>>> static bool is_cxx (const_tree);
>>> static bool is_fortran (void);
>>> @@ -5434,6 +5435,19 @@ get_AT_file (dw_die_ref die, enum dwarf_attribute
>>> attr_kind)
>>> return a ? AT_file (a) : NULL;
>>> }
>>>
>>> +/* Return TRUE if the language is C. */
>>> +
>>> +static inline bool
>>> +is_c (void)
>>> +{
>>> + unsigned int lang = get_AT_unsigned (comp_unit_die (), DW_AT_language);
>>> +
>>> + return (lang == DW_LANG_C || lang == DW_LANG_C89 || lang == DW_LANG_C99
>>> + || lang == DW_LANG_C11 || lang == DW_LANG_ObjC);
>>> +
>>> +
>>> +}
>>> +
>>> /* Return TRUE if the language is C++. */
>>>
>>> static inline bool
>>> @@ -20918,12 +20932,24 @@ add_subscript_info (dw_die_ref type_die, tree
>>> type, bool collapse_p)
>>> dimension arr(N:*)
>>> Since the debugger is definitely going to need to know N
>>> to produce useful results, go ahead and output the lower
>>> - bound solo, and hope the debugger can cope. */
>>> + bound solo, and hope the debugger can cope.
>>> +
>>> + For C and C++, if upper is NULL, this may be a zero-length array
>>> + or a flexible array; we'd like to be able to distinguish between
>>> + the two. Set DW_AT_count to 0 for the former. TYPE_SIZE is NULL
>>> + for the latter. */
>>>
> I found inserting this comment here confusing, I've moved it down and
> shortened it.
>
>>> if (!get_AT (subrange_die, DW_AT_lower_bound))
>>> add_bound_info (subrange_die, DW_AT_lower_bound, lower, NULL);
>>> - if (upper && !get_AT (subrange_die, DW_AT_upper_bound))
>>> - add_bound_info (subrange_die, DW_AT_upper_bound, upper, NULL);
>>> + if (!get_AT (subrange_die, DW_AT_upper_bound)
>>> + && !get_AT (subrange_die, DW_AT_count))
>>> + {
>>> + if (upper)
>>> + add_bound_info (subrange_die, DW_AT_upper_bound, upper, NULL);
>>> + else if ((is_c () || is_cxx ()) && TYPE_SIZE (type))
>>> + add_bound_info (subrange_die, DW_AT_count,
>>> + build_int_cst (TREE_TYPE (lower), 0), NULL);
>>> + }
>>> }
>>>
>>> /* Otherwise we have an array type with an unspecified length. The
>> Ping. Does this version look okay for trunk?
>>
> Looks ok to me (but I can't approve).
>
> Also, I've added a testcase.
>
> OK for trunk?
>
Ping.
Thanks,
- Tom
>
>
> 0001-debug-DWARF-add-DW_AT_count-to-zero-length-arrays.patch
>
> [debug] DWARF: add DW_AT_count to zero-length arrays
>
> 2018-09-04 Omar Sandoval <osan...@osandov.com>
> Tom de Vries <tdevr...@suse.de>
>
> PR debug/86985
> * dwarf2out.c (is_c): New function.
> (add_subscript_info): Add DW_AT_count of 0 for C zero-length arrays.
>
> * gcc.dg/guality/zero-length-array.c: New test.
>
> ---
> gcc/dwarf2out.c | 26
> ++++++++++++++++++++++--
> gcc/testsuite/gcc.dg/guality/zero-length-array.c | 21 +++++++++++++++++++
> 2 files changed, 45 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index 77317ed2575..58c3906cdbf 100644
> --- a/gcc/dwarf2out.c
> +++ b/gcc/dwarf2out.c
> @@ -3679,6 +3679,7 @@ static const char *get_AT_string (dw_die_ref, enum
> dwarf_attribute);
> static int get_AT_flag (dw_die_ref, enum dwarf_attribute);
> static unsigned get_AT_unsigned (dw_die_ref, enum dwarf_attribute);
> static inline dw_die_ref get_AT_ref (dw_die_ref, enum dwarf_attribute);
> +static bool is_c (void);
> static bool is_cxx (void);
> static bool is_cxx (const_tree);
> static bool is_fortran (void);
> @@ -5442,6 +5443,19 @@ get_AT_file (dw_die_ref die, enum dwarf_attribute
> attr_kind)
> return a ? AT_file (a) : NULL;
> }
>
> +/* Return TRUE if the language is C. */
> +
> +static inline bool
> +is_c (void)
> +{
> + unsigned int lang = get_AT_unsigned (comp_unit_die (), DW_AT_language);
> +
> + return (lang == DW_LANG_C || lang == DW_LANG_C89 || lang == DW_LANG_C99
> + || lang == DW_LANG_C11 || lang == DW_LANG_ObjC);
> +
> +
> +}
> +
> /* Return TRUE if the language is C++. */
>
> static inline bool
> @@ -20952,8 +20966,16 @@ add_subscript_info (dw_die_ref type_die, tree type,
> bool collapse_p)
>
> if (!get_AT (subrange_die, DW_AT_lower_bound))
> add_bound_info (subrange_die, DW_AT_lower_bound, lower, NULL);
> - if (upper && !get_AT (subrange_die, DW_AT_upper_bound))
> - add_bound_info (subrange_die, DW_AT_upper_bound, upper, NULL);
> + if (!get_AT (subrange_die, DW_AT_upper_bound)
> + && !get_AT (subrange_die, DW_AT_count))
> + {
> + if (upper)
> + add_bound_info (subrange_die, DW_AT_upper_bound, upper, NULL);
> + else if ((is_c () || is_cxx ()) && TYPE_SIZE (type))
> + /* Zero-length array. */
> + add_bound_info (subrange_die, DW_AT_count,
> + build_int_cst (TREE_TYPE (lower), 0), NULL);
> + }
> }
>
> /* Otherwise we have an array type with an unspecified length. The
> diff --git a/gcc/testsuite/gcc.dg/guality/zero-length-array.c
> b/gcc/testsuite/gcc.dg/guality/zero-length-array.c
> new file mode 100644
> index 00000000000..33f34d98ac2
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/guality/zero-length-array.c
> @@ -0,0 +1,21 @@
> +/* PR debug/86985 */
> +/* { dg-do run } */
> +/* { dg-options "-g" } */
> +
> +struct {
> + int foo;
> + int bar[0];
> +} zla; /* Zero length array. */
> +
> +struct {
> + int foo;
> + int bar[];
> +} fam; /* Flexible array member. */
> +
> +int
> +main ()
> +{
> + /* { dg-final { gdb-test . "type:zla" "struct { int foo; int bar[0]; }" }
> } */
> + /* { dg-final { gdb-test . "type:fam" "struct { int foo; int bar[]; }" } }
> */
> + return 0;
> +}
>
