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I noticed this problem while preparing the initial submission for the ROCm GDB port. One particularity of this patch set is that it does not support unwinding frames, that requires support of some DWARF extensions that will come later. It was still possible to run to a breakpoint and print frame #0, though. When rebasing on top of the frame_info_ptr work, GDB started tripping on a prepare_reinflate call, making it not possible anymore to event print the frame when stopping on a breakpoint. One thing to know about frame 0 is that its id is lazily computed when something requests it through get_frame_id. See:23912acd40/gdb/frame.c (L2070-2080)So, up to that prepare_reinflate call, frame 0's id was not computed, and prepare_reinflate, calling get_frame_id, forces it to be computed. Computing the frame id generally requires unwinding the previous frame, which with my ROCm GDB patch fails. An exception is thrown and the printing of the frame is simply abandonned. Regardless of this ROCm GDB problem (which is admittedly temporary, it will be possible to unwind with subsequent patches), we want to avoid prepare_reinflate to force the computing of the frame id, for the same reasons we lazily compute it in the first place. In addition, frame 0's id is subject to change across a frame cache reset. This is why save_selected_frame and restore_selected_frame have special handling for frame 0:23912acd40/gdb/frame.c (L1841-1863)For this last reason, we also need to handle frame 0 specially in prepare_reinflate / reinflate. Because the frame id of frame 0 can change across a frame cache reset, we must not rely on the frame id from that frame to reinflate it. We should instead just re-fetch the current frame at that point. This patch adds a frame_info_ptr::m_cached_level field, set in frame_info_ptr::prepare_reinflate, so we can tell if a frame is frame 0. There are cases where a frame_info_ptr object wraps a sentinel frame, for which frame_relative_level returns -1, so I have chosen the value -2 to represent "invalid frame level", for when the frame_info_ptr object is empty. In frame_info_ptr::prepare_reinflate, only cache the frame id if the frame level is not 0. It's fine to cache the frame id for the sentinel frame, it will be properly handled by frame_find_by_id later. In frame_info_ptr::reinflate, if the frame level is 0, call get_current_frame to get the target's current frame. Otherwise, use frame_find_by_id just as before. This patch should not have user-visible changes with upstream GDB. But it will avoid forcing the computation of frame 0's when calling prepare_reinflate. And, well, it fixes the upcoming ROCm GDB patch series. Change-Id: I176ed7ee9317ddbb190acee8366e087e08e4d266 Reviewed-By: Bruno Larsen <blarsen@redhat.com>
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.