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/*
american fuzzy lop - high-performance binary-only instrumentation
-----------------------------------------------------------------
Written by Andrew Griffiths <agriffiths@google.com> and
Michal Zalewski <lcamtuf@google.com>
Idea & design very much by Andrew Griffiths.
TCG instrumentation and block chaining support by Andrea Biondo
<andrea.biondo965@gmail.com>
Copyright 2015, 2016, 2017 Google Inc. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at:
http://www.apache.org/licenses/LICENSE-2.0
This code is a shim patched into the separately-distributed source
code of QEMU 2.10.0. It leverages the built-in QEMU tracing functionality
to implement AFL-style instrumentation and to take care of the remaining
parts of the AFL fork server logic.
The resulting QEMU binary is essentially a standalone instrumentation
tool; for an example of how to leverage it for other purposes, you can
have a look at afl-showmap.c.
*/
#include "../../config.h"
#include "tcg-op.h"
/* Declared in afl-qemu-cpu-inl.h */
extern unsigned char *afl_area_ptr;
extern unsigned int afl_inst_rms;
extern abi_ulong afl_start_code, afl_end_code;
/* Generates TCG code for AFL's tracing instrumentation. */
static void afl_gen_trace(target_ulong cur_loc)
{
static __thread target_ulong prev_loc;
TCGv index, count, new_prev_loc;
TCGv_ptr prev_loc_ptr, count_ptr;
/* Optimize for cur_loc > afl_end_code, which is the most likely case on
Linux systems. */
if (cur_loc > afl_end_code || cur_loc < afl_start_code || !afl_area_ptr)
return;
/* Looks like QEMU always maps to fixed locations, so ASAN is not a
concern. Phew. But instruction addresses may be aligned. Let's mangle
the value to get something quasi-uniform. */
cur_loc = (cur_loc >> 4) ^ (cur_loc << 8);
cur_loc &= MAP_SIZE - 1;
/* Implement probabilistic instrumentation by looking at scrambled block
address. This keeps the instrumented locations stable across runs. */
if (cur_loc >= afl_inst_rms) return;
/* index = prev_loc ^ cur_loc */
prev_loc_ptr = tcg_const_ptr(&prev_loc);
index = tcg_temp_new();
tcg_gen_ld_tl(index, prev_loc_ptr, 0);
tcg_gen_xori_tl(index, index, cur_loc);
/* afl_area_ptr[index]++ */
count_ptr = tcg_const_ptr(afl_area_ptr);
tcg_gen_add_ptr(count_ptr, count_ptr, TCGV_NAT_TO_PTR(index));
count = tcg_temp_new();
tcg_gen_ld8u_tl(count, count_ptr, 0);
tcg_gen_addi_tl(count, count, 1);
tcg_gen_st8_tl(count, count_ptr, 0);
/* prev_loc = cur_loc >> 1 */
new_prev_loc = tcg_const_tl(cur_loc >> 1);
tcg_gen_st_tl(new_prev_loc, prev_loc_ptr, 0);
}
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