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ARM: kprobes: Optimise emulation of LDM and STM

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This patch improves the performance of LDM and STM instruction
emulation. This is desirable because.

- jprobes and kretprobes probe the first instruction in a function and,
  when the frame pointer is omitted, this instruction is often a STM
  used to push registers onto the stack.

- The STM and LDM instructions are common in the body and tail of
  functions.

- At the same time as being a common instruction form, they also have
  one of the slowest and most complicated simulation routines.

The approach taken to optimisation is to use emulation rather than
simulation, that is, a modified form of the instruction is run with
an appropriate register context.

Benchmarking on an OMAP3530 shows the optimised emulation is between 2
and 3 times faster than the simulation routines. On a Kirkwood based
device the relative performance was very significantly better than this.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
This commit is contained in:
Jon Medhurst 2011-06-14 15:54:28 +01:00 committed by Tixy
parent 235a4ce79f
commit 3d4a99785a
1 changed files with 68 additions and 0 deletions
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68
arch/arm/kernel/kprobes-common.c
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@ -220,13 +220,81 @@ static void __kprobes simulate_ldm1_pc(struct kprobe *p, struct pt_regs *regs)
load_write_pc(regs->ARM_pc, regs);
}
static void __kprobes
emulate_generic_r0_12_noflags(struct kprobe *p, struct pt_regs *regs)
{
register void *rregs asm("r1") = regs;
register void *rfn asm("lr") = p->ainsn.insn_fn;
__asm__ __volatile__ (
"stmdb sp!, {%[regs], r11} \n\t"
"ldmia %[regs], {r0-r12} \n\t"
#if __LINUX_ARM_ARCH__ >= 6
"blx %[fn] \n\t"
#else
"str %[fn], [sp, #-4]! \n\t"
"adr lr, 1f \n\t"
"ldr pc, [sp], #4 \n\t"
"1: \n\t"
#endif
"ldr lr, [sp], #4 \n\t" /* lr = regs */
"stmia lr, {r0-r12} \n\t"
"ldr r11, [sp], #4 \n\t"
: [regs] "=r" (rregs), [fn] "=r" (rfn)
: "0" (rregs), "1" (rfn)
: "r0", "r2", "r3", "r4", "r5", "r6", "r7",
"r8", "r9", "r10", "r12", "memory", "cc"
);
}
static void __kprobes
emulate_generic_r2_14_noflags(struct kprobe *p, struct pt_regs *regs)
{
emulate_generic_r0_12_noflags(p, (struct pt_regs *)(regs->uregs+2));
}
static void __kprobes
emulate_ldm_r3_15(struct kprobe *p, struct pt_regs *regs)
{
emulate_generic_r0_12_noflags(p, (struct pt_regs *)(regs->uregs+3));
load_write_pc(regs->ARM_pc, regs);
}
enum kprobe_insn __kprobes
kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_specific_insn *asi)
{
kprobe_insn_handler_t *handler = 0;
unsigned reglist = insn & 0xffff;
int is_ldm = insn & 0x100000;
int rn = (insn >> 16) & 0xf;
if (rn <= 12 && (reglist & 0xe000) == 0) {
/* Instruction only uses registers in the range R0..R12 */
handler = emulate_generic_r0_12_noflags;
} else if (rn >= 2 && (reglist & 0x8003) == 0) {
/* Instruction only uses registers in the range R2..R14 */
rn -= 2;
reglist >>= 2;
handler = emulate_generic_r2_14_noflags;
} else if (rn >= 3 && (reglist & 0x0007) == 0) {
/* Instruction only uses registers in the range R3..R15 */
if (is_ldm && (reglist & 0x8000)) {
rn -= 3;
reglist >>= 3;
handler = emulate_ldm_r3_15;
}
}
if (handler) {
/* We can emulate the instruction in (possibly) modified form */
asi->insn[0] = (insn & 0xfff00000) | (rn << 16) | reglist;
asi->insn_handler = handler;
return INSN_GOOD;
}
/* Fallback to slower simulation... */
if (reglist & 0x8000)
handler = is_ldm ? simulate_ldm1_pc : simulate_stm1_pc;
else