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? Thanks! 2018-08-16 Omar Sandoval <osan...@osandov.com> * dwarf2out.c (is_c_family): 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..b638942c156 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_family (void); static bool is_cxx (void); static bool is_cxx (const_tree); static bool is_fortran (void); @@ -5434,6 +5435,21 @@ 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 or C++. */ + +static inline bool +is_c_family (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_C_plus_plus + || lang == DW_LANG_ObjC_plus_plus || lang == DW_LANG_C_plus_plus_11 + || lang == DW_LANG_C_plus_plus_14); + + +} + /* Return TRUE if the language is C++. */ static inline bool @@ -20918,12 +20934,24 @@ 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. */ 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_family () && 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
