[binutils-gdb] [gdb/symtab] Fix segfault in process_psymtab_comp_unit

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=248f7165005096fc618c5fd9bf3588719fc589ef

commit 248f7165005096fc618c5fd9bf3588719fc589ef
Author: Tom de Vries <tdevries@suse.de>
Date:   Thu May 27 15:22:38 2021 +0200

    [gdb/symtab] Fix segfault in process_psymtab_comp_unit
    
    When running test-case gdb.dwarf2/dw2-dummy-cu.exp without -readnow, we run
    into:
    ...
    (gdb) file outputs/gdb.dwarf2/dw2-dummy-cu/dw2-dummy-cu^M
    Reading symbols from outputs/gdb.dwarf2/dw2-dummy-cu/dw2-dummy-cu...^M
    ERROR: Couldn't load dw2-dummy-cu into GDB (eof).
    ...
    
    The problem is that we're running into a segfault:
    ...
    Thread 1 "gdb" received signal SIGSEGV, Segmentation fault.
    process_psymtab_comp_unit (this_cu=0x2141090, per_objfile=0x1aa4140,
        want_partial_unit=false, pretend_language=language_minimal)
        at /home/vries/gdb_versions/devel/src/gdb/dwarf2/read.c:7023
    7023      switch (reader.comp_unit_die->tag)
    ...
    due to reader.comp_unit_die == nullptr:
    ...
    (gdb) p reader.comp_unit_die
    $1 = (die_info *) 0x0
    ...
    
    Indeed, there's no CU DIE in the test-case:
    ...
    $ readelf -wi outputs/gdb.dwarf2/dw2-dummy-cu/dw2-dummy-cu
    Contents of the .debug_info section:
    
      Compilation Unit @ offset 0x0:
       Length:        0x7 (32-bit)
       Version:       2
       Abbrev Offset: 0x0
       Pointer Size:  4
    $
    ...
    
    Fix this by handling reader.comp_unit_die == nullptr in
    process_psymtab_comp_unit.
    
    Update the test-case to trigger this PR, as per PR27920 - "[gdb/testsuite]
    hardcoding -readnow skips testing of partial symbols".
    
    Tested on x86_64-linux.
    
    gdb/ChangeLog:
    
    2021-05-27  Tom de Vries  <tdevries@suse.de>
    
            PR symtab/27919
            * dwarf2/read.c (process_psymtab_comp_unit):
    
    gdb/testsuite/ChangeLog:
    
    2021-05-27  Tom de Vries  <tdevries@suse.de>
    
            PR symtab/27919
            PR testsuite/27920
            * gdb.dwarf2/dw2-dummy-cu.exp: Use maint expand-symtabs instead of
            -readnow.

Diff:
---
 gdb/ChangeLog                             | 5 +++++
 gdb/dwarf2/read.c                         | 3 +++
 gdb/testsuite/ChangeLog                   | 7 +++++++
 gdb/testsuite/gdb.dwarf2/dw2-dummy-cu.exp | 6 +-----
 4 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3c0c2db7147..6170d2dc56c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2021-05-27  Tom de Vries  <tdevries@suse.de>
+
+	PR symtab/27919
+	* dwarf2/read.c (process_psymtab_comp_unit):
+
 2021-05-27  Tom de Vries  <tdevries@suse.de>
 
 	* dwarf2/read.c (find_partial_die): Fix "Cannot not" typo in dwarf
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 0da87bbecd6..4cc5b4f32d7 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -7020,6 +7020,9 @@ process_psymtab_comp_unit (dwarf2_per_cu_data *this_cu,
 
   cutu_reader reader (this_cu, per_objfile, nullptr, nullptr, false);
 
+  if (reader.comp_unit_die == nullptr)
+    return;
+
   switch (reader.comp_unit_die->tag)
     {
     case DW_TAG_compile_unit:
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 968e623db40..22a99c0cc5e 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2021-05-27  Tom de Vries  <tdevries@suse.de>
+
+	PR symtab/27919
+	PR testsuite/27920
+	* gdb.dwarf2/dw2-dummy-cu.exp: Use maint expand-symtabs instead of
+	-readnow.
+
 2021-05-27  Tom de Vries  <tdevries@suse.de>
 
 	PR testsuite/27921
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-dummy-cu.exp b/gdb/testsuite/gdb.dwarf2/dw2-dummy-cu.exp
index 673972447a1..7871851e577 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-dummy-cu.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-dummy-cu.exp
@@ -27,13 +27,9 @@ if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" object {}] != "
     return -1
 }
 
-set saved_gdbflags $GDBFLAGS
-set GDBFLAGS "$GDBFLAGS -readnow"
-
 clean_restart $executable
+gdb_test_no_output "maint expand-symtab"
 
 # Something simple to verify gdb didn't crash, and has read in whatever symbol
 # info is there.
 gdb_test "info fun main" "main_end"
-
-set GDBFLAGS $saved_gdbflags