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authorAnju T <anju@linux.vnet.ibm.com>2017-02-08 15:20:51 +0530
committerMichael Ellerman <mpe@ellerman.id.au>2017-02-10 13:28:04 +1100
commit51c9c0843993528bffc920c54c2121d9e6f8b090 (patch)
tree1ffd280d9ca0ce51faaa957d23c1e217ee0e2e20 /arch/powerpc/lib
parent30176466e36aadba01e1a630cf42397a3438efa4 (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.c21
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)
{