On Thu, 13 Sep 2018, Tom de Vries wrote:
> 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 <[email protected]>
> >>>>> 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 <[email protected]>
> >>>
> > 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 <[email protected]>
> > Tom de Vries <[email protected]>
> >
> > 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))
Please use COMPLETE_TYPE_P (type) instead of TYPE_SIZE (type).
I guess the restriction to C/C++ makes sense, at least for those
we know the array element type can never be incomplete...
Thus OK with the above change.
Richard.
> > + /* 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;
> > +}
> >
>
>
--
Richard Biener <[email protected]>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
