tree 8d9a78c0090c59316401c173895dc58b458e9f09
parent 6aaa8b5570c7b5b9eb8913ec80263a1012b1dd66
author Jon Medhurst <tixy@yxit.co.uk> 1308236040 +0100
committer Tixy <tixy@medhuaa1.miniserver.com> 1310578362 +0000

ARM: kprobes: Don't trigger probes on conditional instructions when condition is false

This patch changes the behavior of kprobes on ARM so that:

    Kprobes on conditional instructions don't trigger when the
    condition is false. For conditional branches, this means that
    they don't trigger in the branch not taken case.

Rationale:

When probes are placed onto conditionally executed instructions in a
Thumb IT block, they may not fire if the condition is not met. This
is because we use invalid instructions for breakpoints and "it is
IMPLEMENTATION DEFINED whether the instruction executes as a NOP or
causes an Undefined Instruction exception". Therefore, for consistency,
we will ignore all probes on any conditional instructions when the
condition is false. Alternative solutions seem to be too complex to
implement or inconsistent.

This issue was discussed on linux.arm.kernel in the thread titled
"[RFC] kprobes with thumb2 conditional code" See
http://comments.gmane.org/gmane.linux.linaro.devel/2985

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>