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The UNWIND_SAME_ID check is done between THIS_FRAME and the next frame when we go try to unwind the previous frame. But at this point, it's already too late -- we ended up with two frames with the same ID in the frame chain. Each frame having its own ID is an invariant assumed throughout GDB. This patch applies the UNWIND_SAME_ID detection earlier, right after the previous frame is unwound, discarding the dup frame if a cycle is detected. The patch includes a new test that fails before the change. Before the patch, the test causes an infinite loop in GDB, after the patch, the UNWIND_SAME_ID logic kicks in and makes the backtrace stop with: Backtrace stopped: previous frame identical to this frame (corrupt stack?) The test uses dwarf CFI to emulate a corrupted stack with a cycle. It has a function with registers marked DW_CFA_same_value (most importantly RSP/RIP), so that GDB computes the same ID for that frame and its caller. IOW, something like this: #0 - frame_id_1 #1 - frame_id_2 #2 - frame_id_3 #3 - frame_id_4 #4 - frame_id_4 <<<< outermost (UNWIND_SAME_ID). (The test's code is just a copy of dw2-reg-undefined.S / dw2-reg-undefined.c, adjusted to use DW_CFA_same_value instead of DW_CFA_undefined, and to mark a different set of registers.) The infinite loop is here, in value_fetch_lazy: while (VALUE_LVAL (new_val) == lval_register && value_lazy (new_val)) { frame = frame_find_by_id (VALUE_FRAME_ID (new_val)); ... new_val = get_frame_register_value (frame, regnum); } get_frame_register_value can return a lazy register value pointing to the next frame. This means that the register wasn't clobbered by FRAME; the debugger should therefore retrieve its value from the next frame. To be clear, get_frame_register_value unwinds the value in question from the next frame: struct value * get_frame_register_value (struct frame_info *frame, int regnum) { return frame_unwind_register_value (frame->next, regnum); ^^^^^^^^^^^ } In other words, if we get a lazy lval_register, it should have the frame ID of the _next_ frame, never of FRAME. At this point in value_fetch_lazy, the whole relevant chunk of the stack up to frame #4 has already been unwound. The loop always "unlazies" lval_registers in the "next/innermost" direction, not in the "prev/unwind further/outermost" direction. So say we're looking at frame #4. get_frame_register_value in frame #4 can return a lazy register value of frame #3. So the next iteration, frame_find_by_id tries to read the register from frame #3. But, since frame #4 happens to have same id as frame #3, frame_find_by_id returns frame #4 instead. Rinse, repeat, and we have an infinite loop. This is an old latent problem, exposed by the recent addition of the frame stash. Before we had a stash, frame_find_by_id(frame_id_4) would walk over all frames starting at the current frame, and would always find #3 first. The stash happens to return #4 instead: struct frame_info * frame_find_by_id (struct frame_id id) { struct frame_info *frame, *prev_frame; ... /* Try using the frame stash first. Finding it there removes the need to perform the search by looping over all frames, which can be very CPU-intensive if the number of frames is very high (the loop is O(n) and get_prev_frame performs a series of checks that are relatively expensive). This optimization is particularly useful when this function is called from another function (such as value_fetch_lazy, case VALUE_LVAL (val) == lval_register) which already loops over all frames, making the overall behavior O(n^2). */ frame = frame_stash_find (id); if (frame) return frame; for (frame = get_current_frame (); ; frame = prev_frame) { gdb/ 2013-11-22 Pedro Alves <palves@redhat.com> PR 16155 * frame.c (get_prev_frame_1): Do the UNWIND_SAME_ID check between this frame and the new previous frame, not between this frame and the next frame. gdb/testsuite/ 2013-11-22 Pedro Alves <palves@redhat.com> PR 16155 * gdb.dwarf2/dw2-dup-frame.S: New file. * gdb.dwarf2/dw2-dup-frame.c: New file. * gdb.dwarf2/dw2-dup-frame.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 | ||
| .cvsignore | ||
| .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 | ||
| 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.