dwarf2read.c: Check type of linkage name attribute prior to decoding

  On Mon, 17 Aug 2015 22:45:05 +0000
Doug Evans <dje@google.com> wrote:

> LGTM

Thanks for looking it over!

This is what I've pushed:

commit 7d45c7c3f692d93c3a33a043c347f1386681deb4
Author: Kevin Buettner <kevinb@redhat.com>
Date:   Mon Aug 3 14:17:17 2015 -0700

    dwarf2read.c: Check type of string valued attributes prior to decoding.

    This change introduces a new function, dwarf2_string_attr(), which is
    a wrapper for dwarf2_attr().  dwarf2read.c has been updated to
    call dwarf2_string_attr in most instances where a string-valued
    attribute is decoded to produce a string value.  In most cases, it
    simplifies the code; in some instances, the complexity of the code
    remains unchanged.

    I performed this change by looking for instances where the
    result of DW_STRING was used in an assignment.  Many of these
    had a pattern which (roughly) looks something like this:

      struct attribute *attr = NULL;

      attr = dwarf2_attr (die, name, cu);
      if (attr != NULL && DW_STRING (attr))
        {
          const char *str;
          ...
          str = DW_STRING (attr);
          ... /* Use str in some fashion.  */
        }

    Code of this form is transformed to look like this instead:

      const char *str;

      str = dwarf2_string_attr (die, name, cu)
      if (str != NULL)
        {
           ...
           /* Use str in some fashion.  */
           ...
        }

    In addition to invoking dwarf2_attr() and DW_STRING(),
    dwarf2_string_attr() checks to make sure that the attribute's
    `form' field matches one of DW_FORM_strp, DW_FORM_string, or
    DW_FORM_GNU_strp_alt.  If it does not match one of these forms,
    it will return a NULL value in addition to calling complaint().

    An earlier version of this patch did this type checking for one
    particular instance where a string attribute was being decoded.
    The situation that I was attempting to handle in that earlier patch is
    this:

    The Texas Instruments compiler uses the encoding for
    DW_AT_MIPS_linkage_name for other purposes.  TI uses the encoding,
    0x2007, for TI_AT_TI_end_line which, unlike DW_AT_MIPS_linkage_name,
    does not have a string-typed value.  In this instance, GDB was attempting
    to use an integer value as a string pointer, with predictable results.
    (GDB would die with a segmentation fault.)

    I've added a test which reproduces the problem that I was orignally
    wanting to fix.  It uses DW_AT_MIPS_linkage name with an associate
    value which is a string, and again, where the value is a small
    integer.

    My test case causes GDB to segfault in an unpatched GDB.  There
    will be two PASSes in a patched GDB.

    Unpatched GDB:

    (gdb) ptype f
    ERROR: Process no longer exists
    UNRESOLVED: gdb.dwarf2/dw2-bad-mips-linkage-name.exp: ptype f
    ERROR: Couldn't send ptype g to GDB.
    UNRESOLVED: gdb.dwarf2/dw2-bad-mips-linkage-name.exp: ptype g

    Patched GDB:

    (gdb) ptype f
    type = bool ()
    (gdb) PASS: gdb.dwarf2/dw2-bad-mips-linkage-name.exp: ptype f
    ptype g
    type = bool ()
    (gdb) PASS: gdb.dwarf2/dw2-bad-mips-linkage-name.exp: ptype g

    I see no regressions on an x86_64 native target.

    gdb/ChangeLog:

    	* dwarf2read.c (dwarf2_string_attr): New function.
    	(lookup_dwo_unit, process_psymtab_comp_unit_reader)
    	(dwarf2_compute_name, dwarf2_physname, find_file_and_directory)
    	(read_call_site_scope, namespace_name, guess_full_die_structure_name)
    	(anonymous_struct_prefix, prepare_one_comp_unit): Use
    	dwarf2_string_attr in place of dwarf2_attr and DW_STRING.

    gdb/testsuite/ChangeLog:

    	* gdb.dwarf2/dw2-bad-mips-linkage-name.c: New file.
    	* gdb.dwarf2/dw2-bad-mips-linkage-name.exp: New file.
---
 gdb/ChangeLog                                      |   9 ++
 gdb/dwarf2read.c                                   | 134 +++++++++++----------
 gdb/testsuite/ChangeLog                            |   5 +
 .../gdb.dwarf2/dw2-bad-mips-linkage-name.c         |  41 +++++++
 .../gdb.dwarf2/dw2-bad-mips-linkage-name.exp       |  72 +++++++++++
 5 files changed, 196 insertions(+), 65 deletions(-)

dwarf2read.c: Check type of linkage name attribute prior to decoding

Commit Message

Patch