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Objtool currently only compiles for x86 architectures. This is
fine as it presently does not support tooling for other
architectures. However, we would like to be able to convert other
kernel tools to run as objtool sub commands because they too
process ELF object files. This will allow us to convert tools
such as recordmcount to use objtool's ELF code.
Since much of recordmcount's ELF code is copy-paste code to/from
a variety of other kernel tools (look at modpost for example) this
means that if we can convert recordmcount we can convert more.
We define weak definitions for subcommand entry functions and other weak
definitions for shared functions critical to building existing
subcommands. These return 127 when the command is missing which signify
tools that do not exist on all architectures. In this case the "check"
and "orc" tools do not exist on all architectures so we only add them
for x86. Future changes adding support for "check", to arm64 for
example, can then modify the SUBCMD_CHECK variable when building for
arm64.
Objtool is not currently wired in to KConfig to be built for other
architectures because it's not needed for those architectures and
there are no commands it supports other than those for x86. As more
command support is enabled on various architectures the necessary
KConfig changes can be made (e.g. adding "STACK_VALIDATION") to
trigger building objtool.
[ jpoimboe: remove aliases, add __weak macro, add error messages ]
Cc: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
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All of:
read_symbols(), find_symbol_by_offset(), find_symbol_containing(),
find_containing_func()
do a linear search of the symbols. Add an RB tree to make it go
faster.
This about halves objtool runtime on vmlinux.o, from 34s to 18s.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.499016559@infradead.org
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Fix objtool build, because it adds _ctype dependency via isspace call patch.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: André Goddard Rosa <andre.goddard@gmail.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 7bd330de43fd ("tools lib: Adopt skip_spaces() from the kernel sources")
Link: http://lkml.kernel.org/r/20190702121240.GB12694@krava
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Now that objtool knows the states of all registers on the stack for each
instruction, it's straightforward to generate debuginfo for an unwinder
to use.
Instead of generating DWARF, generate a new format called ORC, which is
more suitable for an in-kernel unwinder. See
Documentation/x86/orc-unwinder.txt for a more detailed description of
this new debuginfo format and why it's preferable to DWARF.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/c9b9f01ba6c5ed2bdc9bb0957b78167fdbf9632e.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In preparation for the new 'objtool undwarf generate' command, which
will rely on 'objtool check', move the checking code from
builtin-check.c to check.c where it can be used by other commands.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Jiri Slaby <jslaby@suse.cz>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/294c5c695fd73c1a5000bbe5960a7c9bec4ee6b4.1498659915.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The objtool build fails in a cross-compiled environment on a non-x86
host with "ARCH=x86_64":
tools/objtool/objtool-in.o: In function `decode_instructions':
tools/objtool/builtin-check.c:276: undefined reference to `arch_decode_instruction'
We could override the ARCH environment variable and change it back to
x86, similar to what the objtool Makefile was doing before; but it's
tricky to override environment variables consistently.
Instead, take a similar approach used by the Linux top-level Makefile
and introduce a SRCARCH Makefile variable which evaluates to "x86" when
ARCH is either "x86_64" or "x86".
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160722191920.ej62fnspnqurbaa7@treble
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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To make it portable to non-glibc systems, that follow the XSI variant
instead of the GNU specific one that gets in place when _GNU_SOURCE is
defined.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-bozcszy93tpgw9ad6qm3dhpx@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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This adds a host tool named objtool which has a "check" subcommand which
analyzes .o files to ensure the validity of stack metadata. It enforces
a set of rules on asm code and C inline assembly code so that stack
traces can be reliable.
For each function, it recursively follows all possible code paths and
validates the correct frame pointer state at each instruction.
It also follows code paths involving kernel special sections, like
.altinstructions, __jump_table, and __ex_table, which can add
alternative execution paths to a given instruction (or set of
instructions). Similarly, it knows how to follow switch statements, for
which gcc sometimes uses jump tables.
Here are some of the benefits of validating stack metadata:
a) More reliable stack traces for frame pointer enabled kernels
Frame pointers are used for debugging purposes. They allow runtime
code and debug tools to be able to walk the stack to determine the
chain of function call sites that led to the currently executing
code.
For some architectures, frame pointers are enabled by
CONFIG_FRAME_POINTER. For some other architectures they may be
required by the ABI (sometimes referred to as "backchain pointers").
For C code, gcc automatically generates instructions for setting up
frame pointers when the -fno-omit-frame-pointer option is used.
But for asm code, the frame setup instructions have to be written by
hand, which most people don't do. So the end result is that
CONFIG_FRAME_POINTER is honored for C code but not for most asm code.
For stack traces based on frame pointers to be reliable, all
functions which call other functions must first create a stack frame
and update the frame pointer. If a first function doesn't properly
create a stack frame before calling a second function, the *caller*
of the first function will be skipped on the stack trace.
For example, consider the following example backtrace with frame
pointers enabled:
[<ffffffff81812584>] dump_stack+0x4b/0x63
[<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
[<ffffffff8127f568>] seq_read+0x108/0x3e0
[<ffffffff812cce62>] proc_reg_read+0x42/0x70
[<ffffffff81256197>] __vfs_read+0x37/0x100
[<ffffffff81256b16>] vfs_read+0x86/0x130
[<ffffffff81257898>] SyS_read+0x58/0xd0
[<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76
It correctly shows that the caller of cmdline_proc_show() is
seq_read().
If we remove the frame pointer logic from cmdline_proc_show() by
replacing the frame pointer related instructions with nops, here's
what it looks like instead:
[<ffffffff81812584>] dump_stack+0x4b/0x63
[<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
[<ffffffff812cce62>] proc_reg_read+0x42/0x70
[<ffffffff81256197>] __vfs_read+0x37/0x100
[<ffffffff81256b16>] vfs_read+0x86/0x130
[<ffffffff81257898>] SyS_read+0x58/0xd0
[<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76
Notice that cmdline_proc_show()'s caller, seq_read(), has been
skipped. Instead the stack trace seems to show that
cmdline_proc_show() was called by proc_reg_read().
The benefit of "objtool check" here is that because it ensures that
*all* functions honor CONFIG_FRAME_POINTER, no functions will ever[*]
be skipped on a stack trace.
[*] unless an interrupt or exception has occurred at the very
beginning of a function before the stack frame has been created,
or at the very end of the function after the stack frame has been
destroyed. This is an inherent limitation of frame pointers.
b) 100% reliable stack traces for DWARF enabled kernels
This is not yet implemented. For more details about what is planned,
see tools/objtool/Documentation/stack-validation.txt.
c) Higher live patching compatibility rate
This is not yet implemented. For more details about what is planned,
see tools/objtool/Documentation/stack-validation.txt.
To achieve the validation, "objtool check" enforces the following rules:
1. Each callable function must be annotated as such with the ELF
function type. In asm code, this is typically done using the
ENTRY/ENDPROC macros. If objtool finds a return instruction
outside of a function, it flags an error since that usually indicates
callable code which should be annotated accordingly.
This rule is needed so that objtool can properly identify each
callable function in order to analyze its stack metadata.
2. Conversely, each section of code which is *not* callable should *not*
be annotated as an ELF function. The ENDPROC macro shouldn't be used
in this case.
This rule is needed so that objtool can ignore non-callable code.
Such code doesn't have to follow any of the other rules.
3. Each callable function which calls another function must have the
correct frame pointer logic, if required by CONFIG_FRAME_POINTER or
the architecture's back chain rules. This can by done in asm code
with the FRAME_BEGIN/FRAME_END macros.
This rule ensures that frame pointer based stack traces will work as
designed. If function A doesn't create a stack frame before calling
function B, the _caller_ of function A will be skipped on the stack
trace.
4. Dynamic jumps and jumps to undefined symbols are only allowed if:
a) the jump is part of a switch statement; or
b) the jump matches sibling call semantics and the frame pointer has
the same value it had on function entry.
This rule is needed so that objtool can reliably analyze all of a
function's code paths. If a function jumps to code in another file,
and it's not a sibling call, objtool has no way to follow the jump
because it only analyzes a single file at a time.
5. A callable function may not execute kernel entry/exit instructions.
The only code which needs such instructions is kernel entry code,
which shouldn't be be in callable functions anyway.
This rule is just a sanity check to ensure that callable functions
return normally.
It currently only supports x86_64. I tried to make the code generic so
that support for other architectures can hopefully be plugged in
relatively easily.
On my Lenovo laptop with a i7-4810MQ 4-core/8-thread CPU, building the
kernel with objtool checking every .o file adds about three seconds of
total build time. It hasn't been optimized for performance yet, so
there are probably some opportunities for better build performance.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/f3efb173de43bd067b060de73f856567c0fa1174.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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