MIPS: tracing: disable uprobe/kprobe on compact branch instructions

Current instruction decoder for uprobe/kprobe handler only handles
branches with delay slots. For compact branches the behaviour is rather
unpredictable - and depending on the encoding of a compact branch
instruction may result in one (or more) of:
- executing an instruction that follows a branch which wasn't in a delay
  slot and shouldn't have been executed
- incorrectly emulating a branch leading to a jump to a wrong location
- unexpected branching out of the single-stepped code and never reaching
  the breakpoint that should terminate the probe handler

Results of these actions are generally unpredictable, but can end up
with a probed application or kernel crash, so disable placing probes on
compact branches until they are handled properly.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14336/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/mips/kernel/probes-common.h b/arch/mips/kernel/probes-common.h
index c979c3790e4c..dd08e41134b6 100644
--- a/arch/mips/kernel/probes-common.h
+++ b/arch/mips/kernel/probes-common.h
@@ -13,6 +13,8 @@
 
 #include <asm/inst.h>
 
+int __insn_is_compact_branch(union mips_instruction insn);
+
 static inline int __insn_has_delay_slot(const union mips_instruction insn)
 {
 	switch (insn.i_format.opcode) {