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powerpc/kprobes: Implement Optprobes

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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>
This commit is contained in:
Anju T 2017-02-08 15:20:51 +05:30 • committed by Michael Ellerman
parent 30176466e3
commit 51c9c08439
7 changed files with 530 additions and 1 deletions
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21
arch/powerpc/lib/code-patching.c
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@ -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)
{