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[libc] Add memcmp / bcmp fuzzers #77741

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16 changes: 16 additions & 0 deletions libc/fuzzing/string/CMakeLists.txt
Original file line number Diff line number Diff line change
Expand Up @@ -24,3 +24,19 @@ add_libc_fuzzer(
libc.src.string.strstr
libc.src.string.strlen
)

add_libc_fuzzer(
memcmp_fuzz
SRCS
memcmp_fuzz.cpp
DEPENDS
libc.src.string.memcmp
)

add_libc_fuzzer(
bcmp_fuzz
SRCS
bcmp_fuzz.cpp
DEPENDS
libc.src.string.bcmp
)
54 changes: 54 additions & 0 deletions libc/fuzzing/string/bcmp_fuzz.cpp
Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
//===-- bcmp_fuzz.cpp ---------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// Fuzzing test for llvm-libc bcmp implementation.
///
//===----------------------------------------------------------------------===//
#include "src/string/bcmp.h"
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

static int reference_bcmp(const void *pa, const void *pb, size_t count)
__attribute__((no_builtin)) {
const auto *a = reinterpret_cast<const unsigned char *>(pa);
const auto *b = reinterpret_cast<const unsigned char *>(pb);
for (size_t i = 0; i < count; ++i, ++a, ++b)
if (*a != *b)
return 1;
return 0;
}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
const auto normalize = [](int value) -> int {
if (value == 0)
return 0;
return 1;
};
// We ignore the last byte is size is odd.
const auto count = size / 2;
const char *a = reinterpret_cast<const char *>(data);
const char *b = reinterpret_cast<const char *>(data) + count;
const int actual = LIBC_NAMESPACE::bcmp(a, b, count);
const int reference = reference_bcmp(a, b, count);
if (normalize(actual) == normalize(reference))
return 0;
const auto print = [](const char *msg, const char *buffer, size_t size) {
printf("%s\"", msg);
for (size_t i = 0; i < size; ++i)
printf("\\x%02x", (uint8_t)buffer[i]);
printf("\"\n");
};
printf("count : %zu\n", count);
print("a : ", a, count);
print("b : ", b, count);
printf("expected : %d\n", reference);
printf("actual : %d\n", actual);
__builtin_trap();
}
59 changes: 59 additions & 0 deletions libc/fuzzing/string/memcmp_fuzz.cpp
Original file line number Diff line number Diff line change
@@ -0,0 +1,59 @@
//===-- memcmp_fuzz.cpp ---------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// Fuzzing test for llvm-libc memcmp implementation.
///
//===----------------------------------------------------------------------===//
#include "src/string/memcmp.h"
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>

static int reference_memcmp(const void *pa, const void *pb, size_t count)
__attribute__((no_builtin)) {
const auto *a = reinterpret_cast<const unsigned char *>(pa);
const auto *b = reinterpret_cast<const unsigned char *>(pb);
for (size_t i = 0; i < count; ++i, ++a, ++b) {
if (*a < *b)
return -1;
else if (*a > *b)
return 1;
}
return 0;
}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
const auto sign = [](int value) -> int {
if (value < 0)
return -1;
if (value > 0)
return 1;
return 0;
};
// We ignore the last byte is size is odd.
const auto count = size / 2;
const char *a = reinterpret_cast<const char *>(data);
const char *b = reinterpret_cast<const char *>(data) + count;
const int actual = LIBC_NAMESPACE::memcmp(a, b, count);
const int reference = reference_memcmp(a, b, count);
if (sign(actual) == sign(reference))
return 0;
const auto print = [](const char *msg, const char *buffer, size_t size) {
printf("%s\"", msg);
for (size_t i = 0; i < size; ++i)
printf("\\x%02x", (uint8_t)buffer[i]);
printf("\"\n");
};
printf("count : %zu\n", count);
print("a : ", a, count);
print("b : ", b, count);
printf("expected : %d\n", reference);
printf("actual : %d\n", actual);
__builtin_trap();
}
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Just noticed this file and couldn't quite figure out what its use is. It looks like maybe it's an artifact of running the fuzz test and forgetting to exclude it from the commit. Is it needed for anything, or should we remove it?

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yes it's an artifact from running the fuzzer, and yes it's safe to remove.

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