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GDB that can debug Mach-Os on Linux
41b56feb50
The VALUE_FRAME_ID macro provides access to a member in struct value that's used to hold the frame id that's used when determining a register's value or when assigning to a register. The underlying member has a long and obscure name. I won't refer to it here, but will simply refer to VALUE_FRAME_ID as if it's the struct value member instead of being a convenient macro. At the moment, without this patch in place, VALUE_FRAME_ID is set in value_of_register_lazy() and several other locations to hold the frame id of the frame passed to those functions. VALUE_FRAME_ID is used in the lval_register case of value_fetch_lazy(). To fetch the register's value, it calls get_frame_register_value() which, in turn, calls frame_unwind_register_value() with frame->next. A python based unwinder may wish to determine the value of a register or evaluate an expression containing a register. When it does this, value_fetch_lazy() will be called under some circumstances. It will attempt to determine the frame id associated with the frame passed to it. In so doing, it will end up back in the frame sniffer of the very same python unwinder that's attempting to learn the value of a register as part of the sniffing operation. This recursion is not desirable. As noted above, when value_fetch_lazy() wants to fetch a register's value, it does so (indirectly) by unwinding from frame->next. With this in mind, a solution suggests itself: Change VALUE_FRAME_ID to hold the frame id associated with the next frame. Then, when it comes time to obtain the value associated with the register, we can simply unwind from the frame corresponding to the frame id stored in VALUE_FRAME_ID. This neatly avoids the python unwinder recursion problem by changing when the "next" operation occurs. Instead of the "next" operation occuring when the register value is fetched, it occurs earlier on when assigning a frame id to VALUE_FRAME_ID. (Thanks to Pedro for this suggestion.) This patch implements this idea. It builds on the patch "Distinguish sentinel frame from null frame". Without that work in place, it's necessary to check for null_id at several places and then obtain the sentinel frame. It also renames most occurences of VALUE_FRAME_ID to VALUE_NEXT_FRAME_ID to reflect the new meaning of this field. There are several uses of VALUE_FRAME_ID which were not changed. In each case, the original meaning of VALUE_FRAME_ID is required to get correct results. In all but one of these uses, either put_frame_register_bytes() or get_frame_register_bytes() is being called with the frame value obtained from VALUE_FRAME_ID. Both of these functions perform some unwinding by performing a "->next" operation on the frame passed to it. If we were to use the new VALUE_NEXT_FRAME_ID macro, this would effectively do two "->next" operations, which is not what we want. The VALUE_FRAME_ID macro has been redefined in terms of VALUE_NEXT_FRAME_ID. It simply fetches the previous frame's id, providing this id as the value of the macro. gdb/ChangeLog: * value.h (VALUE_FRAME_ID): Rename to VALUE_NEXT_FRAME_ID. Update comment. Create new VALUE_FRAME_ID which is defined in terms of VALUE_NEXT_FRAME_ID. (deprecated_value_frame_id_hack): Rename to deprecated_value_next_frame_id_hack. * dwarf2loc.c, findvar.c, frame-unwind.c, sentinel-frame.c, valarith.c, valops.c, value.c: Adjust nearly all occurences of VALUE_FRAME_ID to VALUE_NEXT_FRAME_ID. Add comments for those which did not change. * value.c (struct value): Rename frame_id field to next_frame_id. Update comment. (deprecated_value_frame_id_hack): Rename to deprecated_value_next_frame_id_hack. (value_fetch_lazy): Call frame_unwind_register_value() instead of get_frame_register_value(). * frame.c (get_prev_frame_id_by_id): New function. * frame.h (get_prev_frame_id_by_id): Declare. * dwarf2loc.c (dwarf2_evaluate_loc_desc_full): Make VALUE_NEXT_FRAME_ID refer to the next frame. * findvar.c (value_of_register_lazy): Likewise. (default_value_from_register): Likewise. (value_from_register): Likewise. * frame_unwind.c (frame_unwind_got_optimized): Likewise. * sentinel-frame.c (sentinel_frame_prev_register): Likewise. * value.h (VALUE_FRAME_ID): Update comment describing this macro. |
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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.