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16c3b12f19
One of our users reported an internal error using the "bt full"
command. In their situation, reproducing involved the following
scenario:
(gdb) frame 1
(gdb) bt full
#0 0xf7783430 in __kernel_vsyscall ()
No symbol table info available.
#1 0xf5550aeb in waitpid () at ../sysdeps/unix/syscall-template.S:81
No locals.
[...]
#6 0x0fe83139 in xxxx (arg=...)
[...some locals printed, and then...]
<S17b> =
[...]/dwarf2loc.c:364: internal-error: dwarf_expr_frame_base: Assertion
`framefunc != NULL' failed.
As shown above, the error happens while GDB is trying to print the value
of <S17b>, which is a local string internally generated by the compiler.
For that, it finds that the array lives in memory, and therefore tries
to create a struct value for it via:
case DWARF_VALUE_MEMORY:
{
CORE_ADDR address = dwarf_expr_fetch_address (ctx, 0);
[...]
retval = value_at_lazy (type, address + byte_offset);
Unfortunately for us, TYPE happens to be an array whose bounds
are dynamic. More precisely, the bounds of our arrays are described
in the debugging info as being...
<4><2c1985e>: Abbrev Number: 33 (DW_TAG_subrange_type)
<2c1985f> DW_AT_type : <0x2c1989c>
<2c19863> DW_AT_lower_bound : <0x2c19835>
<2c19867> DW_AT_upper_bound : <0x2c19841>
... which are references to a pair of local variables. For instance,
the lower bound is a reference to the following DIE
<3><2c19835>: Abbrev Number: 32 (DW_TAG_variable)
<2c19836> DW_AT_name : [...]
<2c1983a> DW_AT_type : <0x2c198b4>
<2c1983e> DW_AT_artificial : 1
<2c1983e> DW_AT_location : 2 byte block: 91 58 (DW_OP_fbreg: -40)
As a result of the above, value_at_lazy indirectly triggers
a resolution of TYPE (via value_from_contents_and_address),
which means a resolution of TYPE's bounds, and as seen in
the DW_AT_location attribute above for our bounds, computing
the bound's location requires the frame (its location expression
uses DW_OP_fbreg).
Unfortunately for us, value_at_lazy does not get passed a frame,
we've lost the relevant frame when we try to resolve the array's
bounds. Instead, resolve_dynamic_range gets calls dwarf2_evaluate_property
with NULL as the frame:
static struct type *
resolve_dynamic_range (struct type *dyn_range_type,
struct property_addr_info *addr_stack)
{
[...]
if (dwarf2_evaluate_property (prop, NULL, addr_stack, &value))
^^^^
... which then handles this by using the selected frame instead:
if (frame == NULL && has_stack_frames ())
frame = get_selected_frame (NULL);
In our case, the selected frame happens to be frame #1, which is
a frame where we have a minimal amount of debugging info, and in
particular, no debug info for the function itself. And because of that,
when we try to determine the frame's base...
static void
dwarf_expr_frame_base (void *baton, const gdb_byte **start,
size_t * length)
{
struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
const struct block *bl = get_frame_block (debaton->frame, NULL);
[...]
framefunc = block_linkage_function (bl);
... framefunc ends up being NULL, which triggers the assert
in that same function:
gdb_assert (framefunc != NULL);
This patches avoids the issue by temporarily setting the selected_frame
before printing the locals of each frames.
This patch also adds a small testcase, which reproduces the same
issue, but with a slightly different outcome:
(gdb) bt full
#0 0x000000000040049a in opaque_routine ()
No symbol table info available.
#1 0x0000000000400532 in main () at wrong_frame_bt_full-main.c:20
my_table_size = 3
my_table = <error reading variable my_table (frame address is not available.)>
With this patch, the output becomes:
(gdb) bt full
[...]
my_table = {0, 1, 2}
gdb/ChangeLog:
* stack.c (print_frame_local_vars): Temporarily set the selected
frame to FRAME while printing the frame's local variables.
gdb/testsuite/ChangeLog:
* gdb.base/wrong_frame_bt_full-main.c: New file.
* gdb.base/wrong_frame_bt_full-opaque.c: New file.
* gdb.base/wrong_frame_bt_full.exp: New file.
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| bfd | ||
| binutils | ||
| config | ||
| cpu | ||
| elfcpp | ||
| etc | ||
| gas | ||
| gdb | ||
| gold | ||
| gprof | ||
| include | ||
| intl | ||
| ld | ||
| libdecnumber | ||
| libiberty | ||
| opcodes | ||
| readline | ||
| sim | ||
| texinfo | ||
| zlib | ||
| .cvsignore | ||
| .gitattributes | ||
| .gitignore | ||
| ChangeLog | ||
| compile | ||
| config-ml.in | ||
| config.guess | ||
| config.rpath | ||
| config.sub | ||
| configure | ||
| configure.ac | ||
| COPYING | ||
| COPYING3 | ||
| COPYING3.LIB | ||
| COPYING.LIB | ||
| COPYING.LIBGLOSS | ||
| COPYING.NEWLIB | ||
| depcomp | ||
| djunpack.bat | ||
| install-sh | ||
| libtool.m4 | ||
| lt~obsolete.m4 | ||
| ltgcc.m4 | ||
| ltmain.sh | ||
| ltoptions.m4 | ||
| ltsugar.m4 | ||
| ltversion.m4 | ||
| MAINTAINERS | ||
| Makefile.def | ||
| Makefile.in | ||
| Makefile.tpl | ||
| makefile.vms | ||
| missing | ||
| mkdep | ||
| mkinstalldirs | ||
| move-if-change | ||
| README | ||
| README-maintainer-mode | ||
| setup.com | ||
| src-release.sh | ||
| symlink-tree | ||
| ylwrap | ||
README for GNU development tools This directory contains various GNU compilers, assemblers, linkers, debuggers, etc., plus their support routines, definitions, and documentation. If you are receiving this as part of a GDB release, see the file gdb/README. If with a binutils release, see binutils/README; if with a libg++ release, see libg++/README, etc. That'll give you info about this package -- supported targets, how to use it, how to report bugs, etc. It is now possible to automatically configure and build a variety of tools with one command. To build all of the tools contained herein, run the ``configure'' script here, e.g.: ./configure make To install them (by default in /usr/local/bin, /usr/local/lib, etc), then do: make install (If the configure script can't determine your type of computer, give it the name as an argument, for instance ``./configure sun4''. You can use the script ``config.sub'' to test whether a name is recognized; if it is, config.sub translates it to a triplet specifying CPU, vendor, and OS.) If you have more than one compiler on your system, it is often best to explicitly set CC in the environment before running configure, and to also set CC when running make. For example (assuming sh/bash/ksh): CC=gcc ./configure make A similar example using csh: setenv CC gcc ./configure make Much of the code and documentation enclosed is copyright by the Free Software Foundation, Inc. See the file COPYING or COPYING.LIB in the various directories, for a description of the GNU General Public License terms under which you can copy the files. REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info on where and how to report problems.