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The three targets that implement gdbarch_adjust_breakpoint_address are arm, frv, and mips. In each of these targets the adjust breakpoint address function does some combination of reading the symbol table, or reading memory at the location the breakpoint could be placed. The problem is that performing these actions requires that the current inferior and program space be the one in which the breakpoint will be placed, and this is not currently always the case. Consider a GDB session with multiple inferiors. One inferior might be a native target while another could be a remote target of a completely different architecture. Alternatively, if we consider ARM and AArch64, one native inferior might be AArch64, while a second native inferior could be ARM. In these cases it is possible, and valid, for a user to have one inferior selected, and place a breakpoint in the other inferior by placing a breakpoint on a particular symbol. If this happens, then currently, when gdbarch_adjust_breakpoint_address is called, the wrong inferior (and program space) will be selected, and memory reads, and symbol look ups, will not return the expected results, this could lead to breakpoints being placed in the wrong location. There are currently two places where gdbarch_adjust_breakpoint_address is called: 1. In infrun.c, in the function handle_step_into_function. In this case, I believe that the correct inferior and program space will already be selected as this is called as part of the stop event handling, so I don't think we need to worry about this case, and 2. In breakpoint.c, in the function adjust_breakpoint_address, which is itself called from code_breakpoint::add_location and watch_command_1. The watch_command_1 case I don't think we need to worry about, this is for when a local watch expression is created, which can only be in the currently selected inferior, so this case should be fine. The code_breakpoint::add_location case is the one that needs fixing, this is what allows a breakpoint to be created between inferiors. To fix the code_breakpoint::add_location case, I propose that we pass the "correct" program_space (i.e. the program space in which the breakpoint will be created) to the adjust_breakpoint_address function. Then in adjust_breakpoint_address we can make use of switch_to_program_space_and_thread to switch program_space and inferior before calling gdbarch_adjust_breakpoint_address. I discovered this issue while working on a later patch in this series. This later patch will detect when we cast the result of gdbarch_tdep to the wrong type. With this later patch in place I ran gdb.multi/multi-arch.exp on an AArch64 target. In this situation, two inferiors are created, an AArch64 inferior, and an ARM inferior. The test selected the AArch64 inferior and tries to create a breakpoint in the ARM inferior. As a result of this we end up in arm_adjust_breakpoint_address, which calls arm_pc_is_thumb. Before this commit the AArch64 inferior would be current. As a result, all of the checks in arm_pc_is_thumb would fail (they rely on reading symbols from the current program space), and so, at the end of arm_pc_is_thumb we would call arm_frame_is_thumb. However, remember, at this point the current inferior is the AArch64 inferior, so the current frame is an AArch64 frame. In arm_frame_is_thumb we call arm_psr_thumb_bit, which calls gdbarch_tdep and casts the result to arm_gdbarch_tdep. This is wrong, the tdep field is of type aarch64_gdbarch_tdep. After this we have undefined behaviour. With this patch in place, we will have switched to a thread in the ARM program space before calling arm_adjust_breakpoint_address. As a result, we now succeed in looking up the required symbols in arm_pc_is_thumb, and so we never call arm_frame_is_thumb. However, in the worst case scenario, if we did end up calling arm_frame_is_thumb, as the current inferior should now be the ARM inferior, the current frame should be an ARM frame, so we still should not hit undefined behaviour. I have added an assert to arm_frame_is_thumb. |
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| gdb | ||
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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.