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This writes a new value to PC which was obtained as the result of an ARM
ALU instruction. For ARMv7 and later this performs interworking.
On ARM kernels we shouldn't encounter any ALU instructions trying to
switch to Thumb mode so support for this isn't strictly necessary.
However, the approach taken in all other instruction decoding is for us
to avoid unpredictable modification of the PC for security reasons. This
is usually achieved by rejecting insertion of probes on problematic
instruction, but for ALU instructions we can't do this as it depends on
the contents of the CPU registers at the time the probe is hit. So, as
we require some form of run-time checking to trap undesirable PC
modification, we may as well simulate the instructions correctly, i.e.
in the way they would behave in the absence of a probe.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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This patch improves the performance of LDM and STM instruction
emulation. This is desirable because.
- jprobes and kretprobes probe the first instruction in a function and,
when the frame pointer is omitted, this instruction is often a STM
used to push registers onto the stack.
- The STM and LDM instructions are common in the body and tail of
functions.
- At the same time as being a common instruction form, they also have
one of the slowest and most complicated simulation routines.
The approach taken to optimisation is to use emulation rather than
simulation, that is, a modified form of the instruction is run with
an appropriate register context.
Benchmarking on an OMAP3530 shows the optimised emulation is between 2
and 3 times faster than the simulation routines. On a Kirkwood based
device the relative performance was very significantly better than this.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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The encoding of these instructions is substantially the same for both
ARM and Thumb, so we can have common decoding and simulation functions.
This patch moves the simulation functions from kprobes-arm.c to
kprobes-common.c. It also adds a new simulation function
(simulate_ldm1_pc) for the case where we load into PC because this may
need to interwork.
The instruction decoding is done by a custom function
(kprobe_decode_ldmstm) rather than just relying on decoding table
entries because we will later be adding optimisation code.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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This writes a value to PC which was obtained as the result of a
LDR or LDM instruction. For ARMv5T and later this must perform
interworking.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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For hints which may have observable effects, like SEV (send event), we
use kprobe_emulate_none which emulates the hint by executing the
original instruction.
For NOP we simulate the instruction using kprobe_simulate_nop, which
does nothing. As probes execute with interrupts disabled this is also
used for hints which may block for an indefinite time, like WFE (wait
for event).
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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The existing ARM instruction decoding functions are a mass of if/else
code. Rather than follow this pattern for Thumb instruction decoding
this patch implements an infrastructure for a new table driven scheme.
This has several advantages:
- Reduces the kernel size by approx 2kB. (The ARM instruction decoding
will eventually have -3.1kB code, +1.3kB data; with similar or better
estimated savings for Thumb decoding.)
- Allows programmatic checking of decoding consistency and test case
coverage.
- Provides more uniform source code and is therefore, arguably, clearer.
For a detailed explanation of how decoding tables work see the in-source
documentation in kprobes.h, and also for kprobe_decode_insn().
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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The str_pc_offset value is architecturally defined on ARMv7 onwards so
we can make it a compile time constant. This means on Thumb kernels the
runtime checking code isn't needed, which saves us from having to fix it
to work for Thumb.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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Move str_pc_offset into kprobes-common.c as it will be needed by common
code later.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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This file will contain the instruction decoding and emulation code
which is common to both ARM and Thumb instruction sets.
For now, we will just move over condition_checks from kprobes-arm.c
This table is also renamed to kprobe_condition_checks to avoid polluting
the public namespace with a too generic name.
Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
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