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// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif
#include "components/gwp_asan/common/pack_stack_trace.h"
namespace gwp_asan {
namespace internal {
namespace {
// Encode variable-length integer to |out|, returns 0 if there was not enough
// space to finish writing it or the length of the encoded integer otherwise.
size_t VarIntEncode(uintptr_t value, uint8_t* out, size_t out_len) {
for (size_t i = 0; i < out_len; i++) {
out[i] = value & 0x7f;
value >>= 7;
if (!value)
return i + 1;
out[i] |= 0x80;
}
return 0;
}
// Decode a variable-length integer to |out|, returns 0 if reading it failed or
// the length of the decoded integer otherwise.
size_t VarIntDecode(const uint8_t* in, size_t in_len, uintptr_t* out) {
uintptr_t result = 0;
size_t shift = 0;
for (size_t i = 0; i < in_len; i++) {
result |= static_cast<uintptr_t>(in[i] & 0x7f) << shift;
if (in[i] < 0x80) {
*out = result;
return i + 1;
}
shift += 7;
// Disallow overflowing the range of the output integer.
if (shift >= sizeof(uintptr_t) * 8)
return 0;
}
return 0;
}
uintptr_t ZigzagEncode(uintptr_t value) {
uintptr_t encoded = value << 1;
if (static_cast<intptr_t>(value) >= 0)
return encoded;
return ~encoded;
}
uintptr_t ZigzagDecode(uintptr_t value) {
uintptr_t decoded = value >> 1;
if (!(value & 1))
return decoded;
return ~decoded;
}
} // namespace
size_t Pack(const uintptr_t* unpacked,
size_t unpacked_size,
uint8_t* packed,
size_t packed_max_size) {
size_t idx = 0;
for (size_t cur_depth = 0; cur_depth < unpacked_size; cur_depth++) {
uintptr_t diff = unpacked[cur_depth];
if (cur_depth > 0)
diff -= unpacked[cur_depth - 1];
size_t encoded_len =
VarIntEncode(ZigzagEncode(diff), packed + idx, packed_max_size - idx);
if (!encoded_len)
break;
idx += encoded_len;
}
return idx;
}
size_t Unpack(const uint8_t* packed,
size_t packed_size,
uintptr_t* unpacked,
size_t unpacked_max_size) {
size_t cur_depth;
size_t idx = 0;
for (cur_depth = 0; cur_depth < unpacked_max_size; cur_depth++) {
uintptr_t encoded_diff;
size_t decoded_len =
VarIntDecode(packed + idx, packed_size - idx, &encoded_diff);
if (!decoded_len)
break;
idx += decoded_len;
unpacked[cur_depth] = ZigzagDecode(encoded_diff);
if (cur_depth > 0)
unpacked[cur_depth] += unpacked[cur_depth - 1];
}
if (idx != packed_size && cur_depth != unpacked_max_size)
return 0;
return cur_depth;
}
} // namespace internal
} // namespace gwp_asan
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