Hi Jakub,
On Tue, 2025-01-07 at 20:22 +0100, Jakub Jelinek wrote:
> DWARF has voted in yesterday https://dwarfstd.org/issues/241209.1.html ,
> which is basically just a guarantee that the DWARF 6 draft
> DW_AT_language_{name,version} attribute codes and content of
> https://dwarfstd.org/languages-v6.html can be used as an extension
> in DWARF 5 and won't be changed.
>
> So, this patch is an alternative to the
> https://gcc.gnu.org/pipermail/gcc-patches/2024-November/669671.html
> patch, which had the major problem that it required changing all the
> DWARF consumers to be able to debug C17 or later or C++17 or later
> sources.
Note that most consumers (binutils, gdb, systemtap, valgrind, elfutils)
have already been updated to use the new DW_LANG constants. We can
easily backport that to the last stable releases before gcc 15 is
released.
> This patch uses still DWARF 5 DW_LANG_C11 or DW_LANG_C_plus_plus_14,
> the latest code in DWARF 5 proper, so all DWARF 5 capable consumers
> should be able to deal with that, but additionally emits the
> DWARF 6 attributes so that newer DWARF consumers can see it isn't
> just C++14 but say C++23 or C11 but C23. Consumers which don't know
> those DWARF 6 attributes would just ignore them. This is like any other
> -gno-strict-dwarf extension, except that normally we emit say DWARF 5
> codes where possible only after DWARF 5 is released, while in this case
> there is a guarantee it can be used before DWARF 6 is released.
Code looks ok to me, it is only for C and C++, would be nice to at
least get it for Fortran and Ada too.
> --- gcc/dwarf2out.cc.jj 2025-01-02 11:23:35.541251268 +0100
> +++ gcc/dwarf2out.cc 2025-01-07 10:09:16.866866563 +0100
> @@ -8755,6 +8755,14 @@ break_out_comdat_types (dw_die_ref die)
> unit = new_die (DW_TAG_type_unit, NULL, NULL);
> add_AT_unsigned (unit, DW_AT_language,
> get_AT_unsigned (comp_unit_die (), DW_AT_language));
> + if (unsigned lname = get_AT_unsigned (comp_unit_die (),
> + DW_AT_language_name))
> + {
> + add_AT_unsigned (unit, DW_AT_language_name, lname);
> + add_AT_unsigned (unit, DW_AT_language_version,
> + get_AT_unsigned (comp_unit_die (),
> + DW_AT_language_version));
> + }
This relies on language_name and language_version always being set
together. Which is the case in the code at this time. Should we assert
that?
> @@ -25376,11 +25388,28 @@ gen_compile_unit_die (const char *filena
> language = DW_LANG_C99;
>
> if (dwarf_version >= 5 /* || !dwarf_strict */)
> - if (strcmp (language_string, "GNU C11") == 0
> - || strcmp (language_string, "GNU C17") == 0
> - || strcmp (language_string, "GNU C23") == 0
> - || strcmp (language_string, "GNU C2Y") == 0)
> - language = DW_LANG_C11;
> + {
> + if (strcmp (language_string, "GNU C11") == 0)
> + language = DW_LANG_C11;
> + else if (strcmp (language_string, "GNU C17") == 0)
> + {
> + language = DW_LANG_C11;
> + lname = DW_LNAME_C;
> + lversion = 201710;
> + }
> + else if (strcmp (language_string, "GNU C23") == 0)
> + {
> + language = DW_LANG_C11;
> + lname = DW_LNAME_C;
> + lversion = 202311;
> + }
> + else if (strcmp (language_string, "GNU C2Y") == 0)
> + {
> + language = DW_LANG_C11;
> + lname = DW_LNAME_C;
> + lversion = 202500;
> + }
> + }
The use of language_string (lang_hooks.name) is a little clumsy, but
already part of the current code. In the future it would be nice to
have separate language and version hooks for this.
Personally I would just go with the new DW_LANG_C17/C23 language code,
they will be supported by consumers when gcc 15 is released.
The 00 for the month in C2Y is clever. Does that match the
__STDC_VERSION__ defined?
> @@ -25392,12 +25421,30 @@ gen_compile_unit_die (const char *filena
> language = DW_LANG_C_plus_plus_11;
> else if (strcmp (language_string, "GNU C++14") == 0)
> language = DW_LANG_C_plus_plus_14;
> - else if (strcmp (language_string, "GNU C++17") == 0
> - || strcmp (language_string, "GNU C++20") == 0
> - || strcmp (language_string, "GNU C++23") == 0
> - || strcmp (language_string, "GNU C++26") == 0)
> - /* For now. */
> - language = DW_LANG_C_plus_plus_14;
> + else if (strcmp (language_string, "GNU C++17") == 0)
> + {
> + language = DW_LANG_C_plus_plus_14;
> + lname = DW_LNAME_C_plus_plus;
> + lversion = 201703;
> + }
> + else if (strcmp (language_string, "GNU C++20") == 0)
> + {
> + language = DW_LANG_C_plus_plus_14;
> + lname = DW_LNAME_C_plus_plus;
> + lversion = 202002;
> + }
> + else if (strcmp (language_string, "GNU C++23") == 0)
> + {
> + language = DW_LANG_C_plus_plus_14;
> + lname = DW_LNAME_C_plus_plus;
> + lversion = 202302;
> + }
> + else if (strcmp (language_string, "GNU C++26") == 0)
> + {
> + language = DW_LANG_C_plus_plus_14;
> + lname = DW_LNAME_C_plus_plus;
> + lversion = 202400;
> + }
Why 202400 and not 202600?
Cheers,
Mark
