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Armv8.3-a Pointer Authentication causes the function return address to be
obfuscated on entry to some functions. GDB must unmask the link register in
order to produce a backtrace.
The following patch adds markers of [PAC] to the bracktrace, to indicate
which addresses needed unmasking. This includes the backtrace when using MI.
For example, consider the following backtrace:
(gdb) bt
0 0x0000000000400490 in puts@plt ()
1 0x00000000004005dc in foo ("hello") at cbreak-lib.c:6
2 0x0000000000400604 [PAC] in bar () at cbreak-lib.c:12
3 0x0000000000400620 [PAC] in main2 () at cbreak.c:17
4 0x00000000004005b4 in main () at cbreak-3.c:10
The functions in cbreak-lib use pointer auth, which masks the return address
to the previous function, causing the addresses of bar (in the library) and main2
(in the main binary) to require unmasking in order to unwind the backtrace.
An extra bool is added alongside the prev_pc in the frame structure. At the
point at which the link register is unmasked, the AArch64 port calls into frame
to sets the bool. This is the most efficient way of doing it.
The marker is also added to the python frame printer, which is always printed if
set. The marker is not explicitly exposed to the python code.
I expect this will potentially cause issues with some tests in the testsuite
when Armv8.3 pointer authentication is used. This should be fixed up in the
the future once real hardware is available for full testsuite testing.
gdb/ChangeLog:
* NEWS: Expand the Pointer Authentication entry.
* aarch64-tdep.c (aarch64_frame_unmask_address): Rename from this.
(aarch64_frame_unmask_lr): ... to this.
(aarch64_prologue_prev_register, aarch64_dwarf2_prev_register):
Call aarch64_frame_unmask_lr.
* frame.c (struct frame_info): Add "masked" variable.
(frame_set_previous_pc_masked) (frame_get_pc_masked): New functions.
(fprint_frame): Check for masked pc.
* frame.h (frame_set_previous_pc_masked) (frame_get_pc_masked): New
declarations.
* python/py-framefilter.c (py_print_frame): Check for masked pc.
* stack.c (print_frame): Check for masked pc.
gdb/doc/ChangeLog:
* gdb.texinfo (AArch64 Pointer Authentication): New subsection.
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.