diff options
| author | Anju T <anju@linux.vnet.ibm.com> | 2017-02-08 15:20:51 +0530 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-02-10 13:28:04 +1100 |
| commit | 51c9c0843993528bffc920c54c2121d9e6f8b090 (patch) | |
| tree | 1ffd280d9ca0ce51faaa957d23c1e217ee0e2e20 /arch/powerpc/lib | |
| parent | 30176466e36aadba01e1a630cf42397a3438efa4 (diff) | |
powerpc/kprobes: Implement Optprobes
Current infrastructure of kprobe uses the unconditional trap instruction
to probe a running kernel. Optprobe allows kprobe to replace the trap
with a branch instruction to a detour buffer. Detour buffer contains
instructions to create an in memory pt_regs. Detour buffer also has a
call to optimized_callback() which in turn call the pre_handler(). After
the execution of the pre-handler, a call is made for instruction
emulation. The NIP is determined in advanced through dummy instruction
emulation and a branch instruction is created to the NIP at the end of
the trampoline.
To address the limitation of branch instruction in POWER architecture,
detour buffer slot is allocated from a reserved area. For the time
being, 64KB is reserved in memory for this purpose.
Instructions which can be emulated using analyse_instr() are the
candidates for optimization. Before optimization ensure that the address
range between the detour buffer allocated and the instruction being
probed is within +/- 32MB.
Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/lib')
| -rw-r--r-- | arch/powerpc/lib/code-patching.c | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index 4ccf16a822cc..0899315e1434 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -54,6 +54,27 @@ bool is_offset_in_branch_range(long offset) return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3)); } +/* + * Helper to check if a given instruction is a conditional branch + * Derived from the conditional checks in analyse_instr() + */ +bool __kprobes is_conditional_branch(unsigned int instr) +{ + unsigned int opcode = instr >> 26; + + if (opcode == 16) /* bc, bca, bcl, bcla */ + return true; + if (opcode == 19) { + switch ((instr >> 1) & 0x3ff) { + case 16: /* bclr, bclrl */ + case 528: /* bcctr, bcctrl */ + case 560: /* bctar, bctarl */ + return true; + } + } + return false; +} + unsigned int create_branch(const unsigned int *addr, unsigned long target, int flags) { |