[Bug gdb/21494] New: segfault in find_partial_die_in_comp_unit

["rguenth at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=21494

            Bug ID: 21494
           Summary: segfault in find_partial_die_in_comp_unit
           Product: gdb
           Version: 8.0
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

I get a segfault in find_partial_die_in_comp_unit because cu->partial_dies is
NULL.

#0  find_partial_die_in_comp_unit (sect_off=(unknown: 0), cu=0xfff0e0)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:16369
#1  0x00000000005f91d7 in find_partial_die (sect_off=(unknown: 0), 
    offset_in_dwz=0, cu=0xfd8b50)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:16419
#2  0x00000000005f955f in fixup_partial_die (part_die=0x1023220, cu=0xfd8b50)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:16522
#3  0x00000000005e16f1 in scan_partial_symbols (first_die=0x10231c0, 
    lowpc=0x7fffffffd330, highpc=0x7fffffffd328, set_addrmap=0, cu=0xfd8b50)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:6824
#4  0x00000000005dfe7a in process_psymtab_comp_unit_reader (
    reader=0x7fffffffd460, info_ptr=0x7ffff7fe4de4 "\002", 
    comp_unit_die=0xfef980, has_children=1, data=0x7fffffffd550)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:6183
#5  0x00000000005df125 in init_cutu_and_read_dies (this_cu=0xf1e600, 
    abbrev_table=0x0, use_existing_cu=0, keep=0, 
    die_reader_func=0x5dfb24 <process_psymtab_comp_unit_reader(die_reader_specs
const*, gdb_byte const*, die_info*, int, void*)>, data=0x7fffffffd550)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:5798
#6  0x00000000005e0324 in process_psymtab_comp_unit (this_cu=0xf1e600, 
    want_partial_unit=0, pretend_language=language_minimal)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:6265
#7  0x00000000005e0f8c in dwarf2_build_psymtabs_hard (objfile=0xf1eff0)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:6658
#8  0x00000000005db951 in dwarf2_build_psymtabs (objfile=0xf1eff0)
    at /space/rguenther/src/binutils-gdb/gdb/dwarf2read.c:4407
#9  0x00000000004f0cab in read_psyms (objfile=0xf1eff0)
    at /space/rguenther/src/binutils-gdb/gdb/elfread.c:1290
#10 0x00000000006c7958 in require_partial_symbols (objfile=0xf1eff0, verbose=0)
    at /space/rguenther/src/binutils-gdb/gdb/psymtab.c:87
#11 0x0000000000704d23 in read_symbols (objfile=0xf1eff0, add_flags=...)
    at /space/rguenther/src/binutils-gdb/gdb/symfile.c:883
#12 0x000000000070535a in syms_from_objfile_1 (objfile=0xf1eff0, 
    addrs=0xf1dc20, add_flags=...)
    at /space/rguenther/src/binutils-gdb/gdb/symfile.c:1062
#13 0x00000000007053b2 in syms_from_objfile (objfile=0xf1eff0, addrs=0x0, 
    add_flags=...) at /space/rguenther/src/binutils-gdb/gdb/symfile.c:1078
#14 0x0000000000705753 in symbol_file_add_with_addrs (abfd=0xf1edb0, 
    name=0x7fffffffe2bf "./simple.exe", add_flags=..., addrs=0x0, flags=..., 
    parent=0x0) at /space/rguenther/src/binutils-gdb/gdb/symfile.c:1177
#15 0x0000000000705a48 in symbol_file_add_from_bfd (abfd=0xf1edb0, 
    name=0x7fffffffe2bf "./simple.exe", add_flags=..., addrs=0x0, flags=..., 
    parent=0x0) at /space/rguenther/src/binutils-gdb/gdb/symfile.c:1268
#16 0x0000000000705ac9 in symbol_file_add (name=0x7fffffffe2bf "./simple.exe", 
    add_flags=..., addrs=0x0, flags=...)

we come via

16415         if (per_cu->cu == NULL || per_cu->cu->partial_dies == NULL)
16416  ->       load_partial_comp_unit (per_cu);
16417
16418         per_cu->cu->last_used = 0;
16419         pd = find_partial_die_in_comp_unit (sect_off, per_cu->cu);

but after load_partial_comp_unit the partial_dies hash is not allocated.

The reason is likely invalid DWARF:

  Compilation Unit @ offset 0x15b:
   Length:        0x786c (32-bit)
   Version:       4
   Abbrev Offset: 0x64
   Pointer Size:  8
 <0><166>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <167>   DW_AT_producer    : (indirect string, offset: 0x4c7): GNU GIMPLE
8.0.0 20170515 (experimental) [trunk revision 221942] -mtune=generic
-march=x86-64 -mtune=generic -march=x86-64 -g -g -O2 -O0 -O2 -O0 -fexceptions
-fmath-errno -fsigned-zeros -ftrapping-math -fno-trapv -fno-openmp -fno-openacc
-fmessage-length=0 -fno-show-column -ffunction-sections -fdata-sections
-fltrans
    <16b>   DW_AT_language    : 4       (C++)
    <16c>   DW_AT_name        : (indirect string, offset: 0x2c5): <artificial>
    <170>   DW_AT_comp_dir    : (indirect string, offset: 0x41e):
/abuild/rguenther/obj-early-lto-debug-g/x86_64-pc-linux-gnu/libstdc++-v3/testsuite
    <174>   DW_AT_ranges      : 0x70
    <178>   DW_AT_low_pc      : 0x0
    <180>   DW_AT_stmt_list   : 0xe7
 <1><184>: Abbrev Number: 2 (DW_TAG_imported_unit)
    <185>   DW_AT_import      : <0x0>   [Abbrev Number: 113]

where this import references a non-existing unit.

sth better than just segfaulting should happen here.

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