gdb: avoid dereferencing empty str_offsets_base optional in dwarf_decode_macros

Since 4d7188abfdf2 ("gdbsupport: add debug assertions in
gdb::optional::get"), some macro-related tests fail on Ubuntu 20.04 with
the system gcc 9.3.0 compiler when building with _GLIBCXX_DEBUG.  For
example, gdb.base/info-macros.exp results in:

   (gdb) break -qualified main
   /home/smarchi/src/binutils-gdb/gdb/../gdbsupport/gdb_optional.h:206: internal-error: T& gdb::optional<T>::get() [with T = long unsigned int]: Assertion `this->has_value ()' failed.

The binary contains DWARF 4 debug info and includes a pre-standard
(pre-DWARF 5) .debug_macro section.  The CU doesn't have a
DW_AT_str_offsets_base attribute (which doesn't exist in DWARF 4).  The
field dwarf2_cu::str_offsets_base is therefore empty.  At
dwarf2/read.c:24138, we unconditionally read the value in the optional,
which triggers the assertion shown above.

The same thing happens when building the test program with DWARF 5 with
the same gcc compiler, as that version of gcc doesn't use indirect
string forms, even with DWARF 5.  So it still doesn't add a
DW_AT_str_offsets_base attribute on the CU.

Fix that by propagating down a gdb::optional<ULONGEST> for the str
offsets base instead of ULONGEST.  That value is only used in
dwarf_decode_macro_bytes, when encountering an "strx" macro operation
(DW_MACRO_define_strx or DW_MACRO_undef_strx).  Add a check there that
we indeed have a value in the optional before reading it.  This is
unlikely to happen, but could happen in theory with an erroneous file
that uses DW_MACRO_define_strx but does not provide a
DW_AT_str_offsets_base (in practice, some things would probably have
failed before and stopped processing of debug info).  I tested the
complaint by inverting the condition and using a clang-compiled binary,
which uses the strx operators.  This is the result:

    During symbol reading: use of DW_MACRO_define_strx with unknown string offsets base [in module /home/simark/build/binutils-gdb/gdb/testsuite/outputs/gdb.base/info-macros/info-macros]

The test now passes cleanly with the setup mentioned above, and the
testsuite looks on par with how it was before 4d7188abfdf2.

Change-Id: I7ebd2724beb7b9b4178872374c2a177aea696e77

diff --git a/gdb/dwarf2/macro.c b/gdb/dwarf2/macro.c
index bf687daedd71406cedcdbc25686ca79ab990165b..082c4e9672ae872b202efc4e9f9e2c66278712e5 100644 (file)
--- a/gdb/dwarf2/macro.c
+++ b/gdb/dwarf2/macro.c
@@ -429,7 +429,7 @@ dwarf_decode_macro_bytes (dwarf2_per_objfile *per_objfile,
                          unsigned int offset_size,
                          struct dwarf2_section_info *str_section,
                          struct dwarf2_section_info *str_offsets_section,
-                         ULONGEST str_offsets_base,
+                         gdb::optional<ULONGEST> str_offsets_base,
                          htab_t include_hash)
 {
   struct objfile *objfile = per_objfile->objfile;
@@ -575,15 +575,27 @@ dwarf_decode_macro_bytes (dwarf2_per_objfile *per_objfile,
            int offset_index = read_unsigned_leb128 (abfd, mac_ptr, &bytes_read);
            mac_ptr += bytes_read;
 
+           /* Use of the strx operators requires a DW_AT_str_offsets_base.  */
+           if (!str_offsets_base.has_value ())
+             {
+               complaint (_("use of %s with unknown string offsets base "
+                            "[in module %s]"),
+                          (macinfo_type == DW_MACRO_define_strx
+                           ? "DW_MACRO_define_strx"
+                           : "DW_MACRO_undef_strx"),
+                          objfile_name (objfile));
+               break;
+             }
+
            str_offsets_section->read (objfile);
            const gdb_byte *info_ptr = (str_offsets_section->buffer
-                                       + str_offsets_base
+                                       + *str_offsets_base
                                        + offset_index * offset_size);
 
            const char *macinfo_str = (macinfo_type == DW_MACRO_define_strx ?
                                       "DW_MACRO_define_strx" : "DW_MACRO_undef_strx");
 
-           if (str_offsets_base + offset_index * offset_size
+           if (*str_offsets_base + offset_index * offset_size
                >= str_offsets_section->size)
              {
                complaint (_("%s pointing outside of .debug_str_offsets section "
@@ -767,7 +779,8 @@ dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
                     const struct line_header *lh, unsigned int offset_size,
                     unsigned int offset, struct dwarf2_section_info *str_section,
                     struct dwarf2_section_info *str_offsets_section,
-                    ULONGEST str_offsets_base, int section_is_gnu)
+                    gdb::optional<ULONGEST> str_offsets_base,
+                    int section_is_gnu)
 {
   bfd *abfd;
   const gdb_byte *mac_ptr, *mac_end;

diff --git a/gdb/dwarf2/macro.h b/gdb/dwarf2/macro.h
index 5e77c913cadda979e02c37a39c47af824555cb8c..5a05392312490d3cab7cad4e53213e78180fa578 100644 (file)
--- a/gdb/dwarf2/macro.h
+++ b/gdb/dwarf2/macro.h
@@ -30,7 +30,7 @@ extern void dwarf_decode_macros (dwarf2_per_objfile *per_objfile,
                                 unsigned int offset,
                                 dwarf2_section_info *str_section,
                                 dwarf2_section_info *str_offsets_section,
-                                ULONGEST str_offsets_base,
+                                gdb::optional<ULONGEST> str_offsets_base,
                                 int section_is_gnu);
 
 #endif /* GDB_DWARF2_MACRO_H */

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 6f1b453ef455f325e6fc92ece98d3fb6022c617d..acabee3315f8ed356240f4c58745218c76032d1e 100644 (file)
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -24122,7 +24122,7 @@ dwarf_decode_macros (struct dwarf2_cu *cu, unsigned int offset,
 
   struct dwarf2_section_info *str_offsets_section;
   struct dwarf2_section_info *str_section;
-  ULONGEST str_offsets_base;
+  gdb::optional<ULONGEST> str_offsets_base;
 
   if (cu->dwo_unit != nullptr)
     {
@@ -24135,7 +24135,7 @@ dwarf_decode_macros (struct dwarf2_cu *cu, unsigned int offset,
     {
       str_offsets_section = &per_objfile->per_bfd->str_offsets;
       str_section = &per_objfile->per_bfd->str;
-      str_offsets_base = *cu->str_offsets_base;
+      str_offsets_base = cu->str_offsets_base;
     }
 
   dwarf_decode_macros (per_objfile, builder, section, lh,