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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>
QEMU 3.1.0 port, TCG thread-safety and CompareCoverage by Andrea Fioraldi
<andreafioraldi@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 3.1.0. 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;
void tcg_gen_afl_maybe_log_call(target_ulong cur_loc);
void afl_maybe_log(target_ulong cur_loc) {
static __thread abi_ulong prev_loc;
register uintptr_t afl_idx = cur_loc ^ prev_loc;
#if (defined(__x86_64__) || defined(__i386__)) && defined(AFL_QEMU_NOT_ZERO)
asm volatile (
"incb (%0, %1, 1)\n"
"adc $0, (%0, %1, 1)\n"
: /* no out */
: "r" (afl_area_ptr), "r" (afl_idx)
: "memory", "eax"
);
#else
afl_area_ptr[afl_idx]++;
#endif
prev_loc = cur_loc >> 1;
}
/* Generates TCG code for AFL's tracing instrumentation. */
static void afl_gen_trace(target_ulong cur_loc) {
/* 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*/) // not needed because of static dummy buffer
return;
/* Looks like QEMU always maps to fixed locations, so ASLR 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;
tcg_gen_afl_maybe_log_call(cur_loc);
}
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