Re: [PATCH v2 2/7] Dwarf: Fortran, support DW_TAG_entry_point.

Andrew Burgess
2018-11-27T22:09:28Z

* Pawel Wodkowski <pwodkowski@pl.sii.eu> [2018-11-19 22:38:45 +0100]:

> From: Bernhard Heckel <bernhard.heckel@intel.com>
>
> Fortran provides additional entry-points to an subprogram.
> Those entry-points may have only a subset of parameters
> of the original subprogram as well.
> Add support for parsing DW_TAG_entry_point's for Fortran.

As with patch #1 it's probably worth documenting which compilers you
see DW_TAG_entry_point in, along with an example of what the generated
DWARF looks like.

This means that in the future if/when others start to use this DWARF
feature we can figure out which other compilers we need to test.

>
> 2016-06-01 Bernhard Heckel <bernhard.heckel@intel.com>
>
> gdb/Changelog:
> * gdb/dwarf2read.c (add_partial_symbol): Handle DW_TAG_entry_point.
> (add_partial_entry_point): New.
> (add_partial_subprogram): Search for entry_points.
> (process_die): Handle DW_TAG_entry_point.
> (dwarf2_get_pc_bounds): Update low pc from DWARF.
> (load_partial_dies): Save DW_TAG_entry_point's.
> (load_partial_dies): Save DW_TAG_entry_point to hash table.
> (load_partial_dies): Look into child's of DW_TAG_sub_program
> for fortran.
> (new_symbol_full): Process DW_TAG_entry_point.
> (read_type_die_1): Handle DW_TAG_entry_point.
>
> gdb/Testsuite/Changelog:
> * gdb.fortran/entry_point.f90: New.
> * gdb.fortran/entry_point.exp: New.
> ---
> gdb/dwarf2read.c | 98 ++++++++++++++++++++++++++++++-
> gdb/testsuite/gdb.fortran/entry-point.exp | 70 ++++++++++++++++++++++
> gdb/testsuite/gdb.fortran/entry-point.f90 | 48 +++++++++++++++
> 3 files changed, 215 insertions(+), 1 deletion(-)
> create mode 100644 gdb/testsuite/gdb.fortran/entry-point.exp
> create mode 100644 gdb/testsuite/gdb.fortran/entry-point.f90
>
> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
> index 89fd4ae15e80..88e57d7ab68e 100644
> --- a/gdb/dwarf2read.c
> +++ b/gdb/dwarf2read.c
> @@ -1473,6 +1473,10 @@ static void add_partial_module (struct partial_die_info *pdi, CORE_ADDR *lowpc,
> static void add_partial_enumeration (struct partial_die_info *enum_pdi,
> struct dwarf2_cu *cu);
>
> +static void add_partial_entry_point (struct partial_die_info *pdi,
> + CORE_ADDR *lowpc, CORE_ADDR *highpc,
> + int need_pc, struct dwarf2_cu *cu);
> +
> static void add_partial_subprogram (struct partial_die_info *pdi,
> CORE_ADDR *lowpc, CORE_ADDR *highpc,
> int need_pc, struct dwarf2_cu *cu);
> @@ -8876,6 +8880,32 @@ add_partial_symbol (struct partial_die_info *pdi, struct dwarf2_cu *cu)
>
> switch (pdi->tag)
> {
> + case DW_TAG_entry_point:
> + /* Don't know any other language than fortran which is
> + using DW_TAG_entry_point. */
> + if (cu->language == language_fortran)
> + {

I'm not sure the language check is needed here. The description for
DW_TAG_entry_point in the DWARF spec seems pretty generic. I don't
see how a different language would expect significantly different
results, and so, I would suggest we should just add this as general
purpose code.

> + addr = gdbarch_adjust_dwarf2_addr (gdbarch, pdi->lowpc + baseaddr);

When compared to DW_TAG_subprogram, this line doesn't include a '-
baseaddr'. I think that deserves a comment explaining why.

> + /* DW_TAG_entry_point provides an additional entry_point to an
> + existing sub_program. Therefore, we inherit the "external"
> + attribute from the sub_program to which the entry_point
> + belongs to. */
> + if (pdi->die_parent->is_external)
> + add_psymbol_to_list (actual_name, strlen (actual_name),
> + built_actual_name != nullptr,
> + VAR_DOMAIN, LOC_BLOCK,
> + SECT_OFF_TEXT (objfile),
> + &objfile->global_psymbols,
> + addr, cu->language, objfile);
> + else
> + add_psymbol_to_list (actual_name, strlen (actual_name),
> + built_actual_name != nullptr,
> + VAR_DOMAIN, LOC_BLOCK,
> + SECT_OFF_TEXT (objfile),
> + &objfile->static_psymbols,
> + addr, cu->language, objfile);

I think these two add_psymbol_to_list calls, and the two for
DW_TAG_subprogram should be factored out. Just my opinion though...

> + }
> + break;
> case DW_TAG_inlined_subroutine:
> case DW_TAG_subprogram:
> addr = (gdbarch_adjust_dwarf2_addr (gdbarch, pdi->lowpc + baseaddr)
> @@ -9082,6 +9112,17 @@ add_partial_module (struct partial_die_info *pdi, CORE_ADDR *lowpc,
> scan_partial_symbols (pdi->die_child, lowpc, highpc, set_addrmap, cu);
> }
>
> +static void
> +add_partial_entry_point (struct partial_die_info *pdi,
> + CORE_ADDR *p_lowpc, CORE_ADDR *p_highpc,
> + int set_addrmap, struct dwarf2_cu *cu)
> +{
> + if (pdi->name == nullptr)
> + complaint (_("DW_TAG_entry_point must have a name"));
> + else
> + add_partial_symbol (pdi, cu);
> +}

This function should have a header comment, however, a quick look at
add_partial_subprogram seems to indicate that at this point GDB is not
complaining, but just ignoring weird looking DWARF. For example this
code in add_partial_subprogram:

/* Ignore subprogram DIEs that do not have a name, they are
illegal. Do not emit a complaint at this point, we will
do so when we convert this psymtab into a symtab. */
if (pdi->name)
add_partial_symbol (pdi, cu);

I think the same logic should apply for DW_TAG_entry_point maybe? So,
add_partial_entry_point is possibly redundant.

> +
> /* Read a partial die corresponding to a subprogram or an inlined
> subprogram and create a partial symbol for that subprogram.
> When the CU language allows it, this routine also defines a partial
> @@ -9158,6 +9199,16 @@ add_partial_subprogram (struct partial_die_info *pdi,
> pdi = pdi->die_sibling;
> }
> }
> + else if (cu->language == language_fortran)
> + {

Like before, I'm not convinced we should tie this to Fortran...

> + pdi = pdi->die_child;
> + while (pdi != nullptr)
> + {
> + if (pdi->tag == DW_TAG_entry_point)
> + add_partial_entry_point (pdi, lowpc, highpc, set_addrmap, cu);

You can probably just make the add_partial_symbol call directly here
(after a check that pdi->name is not null.

> + pdi = pdi->die_sibling;
> + }
> + }
> }
>
> /* Read a partial die corresponding to an enumeration type. */
> @@ -10596,6 +10647,7 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
> case DW_TAG_type_unit:
> read_type_unit_scope (die, cu);
> break;
> + case DW_TAG_entry_point:
> case DW_TAG_subprogram:
> case DW_TAG_inlined_subroutine:
> read_func_scope (die, cu);
> @@ -14669,6 +14721,26 @@ dwarf2_get_pc_bounds (struct die_info *die, CORE_ADDR *lowpc,
> CORE_ADDR high = 0;
> enum pc_bounds_kind ret;
>
> + if (die->tag == DW_TAG_entry_point)
> + {
> + /* Entry_point is embedded in an subprogram. Therefore, we can use
> + the highpc from it's enveloping subprogram and get the
> + lowpc from DWARF. */
> + if (0 == dwarf2_get_pc_bounds (die->parent, lowpc, highpc, cu, pst))

Compare to 'PC_BOUNDS_NOT_PRESENT' not 0.

> + return PC_BOUNDS_NOT_PRESENT;
> +
> + attr = dwarf2_attr (die, DW_AT_low_pc, cu);
> + if (!attr)
> + {
> + complaint (_("DW_TAG_entry_point is missing DW_AT_low_pc"));
> + return PC_BOUNDS_NOT_PRESENT;
> + }
> + low = attr_value_as_address (attr);
> + *lowpc = low;
> +
> + return PC_BOUNDS_HIGH_LOW;
> + }
> +
> attr_high = dwarf2_attr (die, DW_AT_high_pc, cu);
> if (attr_high)
> {
> @@ -18399,6 +18471,7 @@ load_partial_dies (const struct die_reader_specs *reader,
> && !is_type_tag_for_partial (abbrev->tag)
> && abbrev->tag != DW_TAG_constant
> && abbrev->tag != DW_TAG_enumerator
> + && abbrev->tag != DW_TAG_entry_point
> && abbrev->tag != DW_TAG_subprogram
> && abbrev->tag != DW_TAG_inlined_subroutine
> && abbrev->tag != DW_TAG_lexical_block
> @@ -18529,6 +18602,7 @@ load_partial_dies (const struct die_reader_specs *reader,
>
> if (load_all
> || abbrev->tag == DW_TAG_constant
> + || abbrev->tag == DW_TAG_entry_point
> || abbrev->tag == DW_TAG_subprogram
> || abbrev->tag == DW_TAG_variable
> || abbrev->tag == DW_TAG_namespace
> @@ -18570,7 +18644,9 @@ load_partial_dies (const struct die_reader_specs *reader,
> || last_die->tag == DW_TAG_union_type))
> || (cu->language == language_ada
> && (last_die->tag == DW_TAG_subprogram
> - || last_die->tag == DW_TAG_lexical_block))))
> + || last_die->tag == DW_TAG_lexical_block))
> + || (cu->language == language_fortran
> + && last_die->tag == DW_TAG_subprogram)))
> {
> nesting_level++;
> parent_die = last_die;
> @@ -21442,6 +21518,25 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
> SYMBOL_ACLASS_INDEX (sym) = LOC_LABEL;
> dw2_add_symbol_to_list (sym, cu->list_in_scope);
> break;
> + case DW_TAG_entry_point:
> + /* Don't know any other language than fortran which is
> + using DW_TAG_entry_point. */
> + if (cu->language == language_fortran)
> + {
> + /* SYMBOL_BLOCK_VALUE (sym) will be filled in later by
> + finish_block. */
> + SYMBOL_ACLASS_INDEX (sym) = LOC_BLOCK;
> + /* DW_TAG_entry_point provides an additional entry_point to an
> + existing sub_program. Therefore, we inherit the "external"
> + attribute from the sub_program to which the entry_point
> + belongs to. */
> + attr2 = dwarf2_attr (die->parent, DW_AT_external, cu);
> + if (attr2 && (DW_UNSND (attr2) != 0))
> + list_to_add = cu->builder->get_global_symbols ();
> + else
> + list_to_add = cu->list_in_scope;
> + }
> + break;
> case DW_TAG_subprogram:
> /* SYMBOL_BLOCK_VALUE (sym) will be filled in later by
> finish_block. */
> @@ -22129,6 +22224,7 @@ read_type_die_1 (struct die_info *die, struct dwarf2_cu *cu)
> case DW_TAG_enumeration_type:
> this_type = read_enumeration_type (die, cu);
> break;
> + case DW_TAG_entry_point:
> case DW_TAG_subprogram:
> case DW_TAG_subroutine_type:
> case DW_TAG_inlined_subroutine:
> diff --git a/gdb/testsuite/gdb.fortran/entry-point.exp b/gdb/testsuite/gdb.fortran/entry-point.exp
> new file mode 100644
> index 000000000000..a1f3f2bebdb9
> --- /dev/null
> +++ b/gdb/testsuite/gdb.fortran/entry-point.exp
> @@ -0,0 +1,70 @@
> +# Copyright 2018 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program. If not, see <http://www.gnu.org/licenses/>.
> +
> +if { [skip_fortran_tests] } { return -1 }
> +
> +standard_testfile .f90
> +load_lib "fortran.exp"
> +
> +if {[prepare_for_testing $testfile.exp $testfile $srcfile {debug f90}]} {
> + return -1
> +}
> +
> +if ![runto MAIN__] then {
> + perror "couldn't run to breakpoint MAIN__"
> + continue
> +}
> +
> +# Test if we can set a breakpoint via entry-point name
> +set ept_name "foo"
> +gdb_breakpoint $ept_name
> +gdb_test "continue" \
> + [multi_line "Breakpoint $decimal, $ept_name \\(j=1, k=2, l=3, i1=4\\) at .*" \
> + ".*"] \
> + "continue to breakpoint: $ept_name"
> +
> +gdb_test "print j" "= 1" "print j, entered via $ept_name"
> +gdb_test "print k" "= 2" "print k, entered via $ept_name"
> +gdb_test "print l" "= 3" "print l, entered via $ept_name"
> +gdb_test "print i1" "= 4" "print i1, entered via $ept_name"
> +gdb_test "info args" \
> + [multi_line "j = 1" \
> + "k = 2" \
> + "l = 3" \
> + "i1 = 4"] \
> + "info args, entered via $ept_name"
> +
> +# Test if we can set a breakpoint via function name
> +set ept_name "bar"
> +gdb_breakpoint $ept_name
> +gdb_test "continue" \
> + [multi_line "Breakpoint $decimal, $ept_name \\(i=4, j=5, k=6, i1=7\\) at .*" \
> + ".*"] \
> + "continue to breakpoint: $ept_name"
> +
> +gdb_test "print i" "= 4" "print i, entered via $ept_name"
> +gdb_test "print j" "= 5" "print j, entered via $ept_name"
> +gdb_test "print k" "= 6" "print k, entered via $ept_name"
> +gdb_test "print i1" "= 7" "print i1, entered via $ept_name"
> +
> +set ept_name "tim"
> +gdb_breakpoint $ept_name
> +gdb_test "continue" \
> + [multi_line "Breakpoint $decimal, $ept_name \\(j=1\\) at .*" \
> + ".*"] \
> + "continue to breakpoint: $ept_name"
> +
> +gdb_test "print j" "= 1" "print j, entered via $ept_name"
> +gdb_test "info args" "j = 1" "info args, entered via $ept_name"
> diff --git a/gdb/testsuite/gdb.fortran/entry-point.f90 b/gdb/testsuite/gdb.fortran/entry-point.f90
> new file mode 100644
> index 000000000000..cb663b956982
> --- /dev/null
> +++ b/gdb/testsuite/gdb.fortran/entry-point.f90
> @@ -0,0 +1,48 @@
> +! Copyright 2018 Free Software Foundation, Inc.
> +!
> +! This program is free software; you can redistribute it and/or modify
> +! it under the terms of the GNU General Public License as published by
> +! the Free Software Foundation; either version 3 of the License, or
> +! (at your option) any later version.
> +!
> +! This program is distributed in the hope that it will be useful,
> +! but WITHOUT ANY WARRANTY; without even the implied warranty of
> +! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +! GNU General Public License for more details.
> +!
> +! You should have received a copy of the GNU General Public License
> +! along with this program. If not, see <http://www.gnu.org/licenses/>.
> +
> +program TestEntryPoint
> +
> + call foo(1,2,3,4)
> + call bar(4,5,6,7)
> + call tim(1)
> +
> +end program TestEntryPoint
> +
> + subroutine bar(I,J,K,I1)
> + INTEGER I,J,K,L,I1
> + INTEGER A
> + REAL C
> +
> + A = 0
> + C = 0.0
> +
> + A = I + K + I1
> + goto 1000
> +
> + entry foo(J,K,L,I1)
> + A = J + K + L + I1
> +
> +200 C = J
> + goto 1000
> +
> + entry tim(J)
> + goto 200
> +
> +1000 A = C + 1
> + C = J * 1.5
> +
> + return
> + end subroutine
> --
> 2.7.4
>

Thanks,
Andrew