From 8f53ac47d3f9c3800c8429d9187961ba81707d8b Mon Sep 17 00:00:00 2001 From: Tom de Vries Date: Wed, 16 Aug 2023 23:43:25 +0200 Subject: [PATCH 1/2] [gdb/symtab] Handle self-reference DIE While working on a dwarf assembly test-case I accidentally created the following pathological dwarf: ... <1>: Abbrev Number: 3 (DW_TAG_class_type) DW_AT_name : c1 DW_AT_specification: <0xbe> ... and noticed gdb segfaulting during cooked index creating due to running out of stack. This is a regression from gdb-12, where gdb just hung. Fix this by inhibiting the scan_attributes self-recursion for self-references. The same test-case with -readnow makes gdb hang, so also fix this in dwarf2_attr and follow_die_ref. Note that this doesn't fix the same problems for the more complicated case of: ... <1>: Abbrev Number: 3 (DW_TAG_class_type) DW_AT_name : c1 DW_AT_specification: <0xc6> <1>: Abbrev Number: 4 (DW_TAG_class_type) DW_AT_name : c2 DW_AT_specification: <0xbe> ... but the approach for deciding whether to fix pathological dwarf cases is as per PR27981 comment 3: ... yes if it is cheap/obvious, and no if it is something complicated or expensive. ... and at this point I'm not sure whether fixing this will fall in the first category. Tested on x86_64-linux. Approved-By: Tom Tromey --- gdb/dwarf2/read.c | 22 +++++++++-- gdb/testsuite/gdb.dwarf2/self-spec.exp | 54 ++++++++++++++++++++++++++ 2 files changed, 73 insertions(+), 3 deletions(-) create mode 100644 gdb/testsuite/gdb.dwarf2/self-spec.exp diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 61f4bd75013..1be5f381432 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -18289,9 +18289,15 @@ cooked_indexer::scan_attributes (dwarf2_per_cu_data *scanning_per_cu, new_info_ptr, &bytes_read); new_info_ptr += bytes_read; - scan_attributes (scanning_per_cu, new_reader, new_info_ptr, new_info_ptr, - new_abbrev, name, linkage_name, flags, nullptr, - parent_entry, maybe_defer, true); + + if (new_reader->cu == reader->cu && new_info_ptr == watermark_ptr) + { + /* Self-reference, we're done. */ + } + else + scan_attributes (scanning_per_cu, new_reader, new_info_ptr, + new_info_ptr, new_abbrev, name, linkage_name, + flags, nullptr, parent_entry, maybe_defer, true); } } @@ -19783,7 +19789,11 @@ dwarf2_attr (struct die_info *die, unsigned int name, struct dwarf2_cu *cu) if (!spec) break; + struct die_info *prev_die = die; die = follow_die_ref (die, spec, &cu); + if (die == prev_die) + /* Self-reference, we're done. */ + break; } return NULL; @@ -22521,6 +22531,12 @@ follow_die_ref (struct die_info *src_die, const struct attribute *attr, struct dwarf2_cu *cu = *ref_cu; struct die_info *die; + if (attr->form != DW_FORM_GNU_ref_alt && src_die->sect_off == sect_off) + { + /* Self-reference, we're done. */ + return src_die; + } + die = follow_die_offset (sect_off, (attr->form == DW_FORM_GNU_ref_alt || cu->per_cu->is_dwz), diff --git a/gdb/testsuite/gdb.dwarf2/self-spec.exp b/gdb/testsuite/gdb.dwarf2/self-spec.exp new file mode 100644 index 00000000000..77e92549fd1 --- /dev/null +++ b/gdb/testsuite/gdb.dwarf2/self-spec.exp @@ -0,0 +1,54 @@ +# Copyright 2023 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 . + +# Check that gdb doesn't hang or segfault on reading a DIE with a +# specification reference to itself. + +load_lib dwarf.exp + +if {![dwarf2_support]} { + return 0 +} + +standard_testfile main.c .S + +# Create the DWARF. +set asm_file [standard_output_file $srcfile2] +Dwarf::assemble $asm_file { + cu {} { + compile_unit {{language @DW_LANG_C_plus_plus}} { + declare_labels c1 + c1: class_type { + {name c1} + {specification :$c1} + } + } + } +} + +if [prepare_for_testing "failed to prepare" $testfile "${asm_file} ${srcfile}" {}] { + return -1 +} + +set index [have_index $binfile] +if { ![string eq $index ""] } { + return 0 +} + +if { [readnow] } { + return 0 +} + +gdb_test "maint expand-symtabs" base-commit: 6c9e159dbd1a35aafa134fcd52982174236a8dd9 -- 2.35.3