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author | Michael Jones <michaelrj@google.com> | 2023-04-27 10:43:10 -0700 |
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committer | Michael Jones <michaelrj@google.com> | 2023-04-28 13:50:40 -0700 |
commit | 377b82a088d46e6124e94605eb62c3ca37046f3b (patch) | |
tree | 7e0bb125d154d82ac1c6d4d3592833d8771b32f1 /libc/fuzzing | |
parent | bf12b746372a25c5a15fa9bd452bd469cc047b47 (diff) | |
download | llvm-377b82a088d46e6124e94605eb62c3ca37046f3b.zip llvm-377b82a088d46e6124e94605eb62c3ca37046f3b.tar.gz llvm-377b82a088d46e6124e94605eb62c3ca37046f3b.tar.bz2 |
[libc] add exception to atof differential fuzz
The differential fuzzer for atof found a bug in glibc's handling of
hexadecimal rounding. Since we can't easily update glibc and we want to
avoid false positives when running the fuzzer, I've added an exception
to skip all hexadecimal subnormal cases.
Reviewed By: sivachandra
Differential Revision: https://reviews.llvm.org/D149359
Diffstat (limited to 'libc/fuzzing')
-rw-r--r-- | libc/fuzzing/stdlib/CMakeLists.txt | 2 | ||||
-rw-r--r-- | libc/fuzzing/stdlib/atof_differential_fuzz.cpp | 39 |
2 files changed, 40 insertions, 1 deletions
diff --git a/libc/fuzzing/stdlib/CMakeLists.txt b/libc/fuzzing/stdlib/CMakeLists.txt index 3127848..785efd8 100644 --- a/libc/fuzzing/stdlib/CMakeLists.txt +++ b/libc/fuzzing/stdlib/CMakeLists.txt @@ -14,6 +14,8 @@ add_libc_fuzzer( StringParserOutputDiff.h DEPENDS libc.src.stdlib.atof + COMPILE_OPTIONS + -DLLVM_LIBC_ATOF_DIF_FUZZ_SKIP_GLIBC_HEX_SUBNORMAL_ERR ) add_libc_fuzzer( diff --git a/libc/fuzzing/stdlib/atof_differential_fuzz.cpp b/libc/fuzzing/stdlib/atof_differential_fuzz.cpp index b368129..2f330e1 100644 --- a/libc/fuzzing/stdlib/atof_differential_fuzz.cpp +++ b/libc/fuzzing/stdlib/atof_differential_fuzz.cpp @@ -16,6 +16,40 @@ #include "fuzzing/stdlib/StringParserOutputDiff.h" +// TODO: Remove this once glibc fixes hex subnormal rounding. See +// https://sourceware.org/bugzilla/show_bug.cgi?id=30220 +#ifdef LLVM_LIBC_ATOF_DIF_FUZZ_SKIP_GLIBC_HEX_SUBNORMAL_ERR +#include <ctype.h> +constexpr double MIN_NORMAL = 0x1p-1022; + +bool has_hex_prefix(const uint8_t *str) { + size_t index = 0; + + // Skip over leading whitespace + while (isspace(str[index])) { + ++index; + } + // Skip over sign + if (str[index] == '-' || str[index] == '+') { + ++index; + } + return str[index] == '0' && (tolower(str[index + 1])) == 'x'; +} + +bool should_be_skipped(const uint8_t *str) { + double init_result = ::atof(reinterpret_cast<const char *>(str)); + if (init_result < 0) { + init_result = -init_result; + } + if (init_result < MIN_NORMAL && init_result != 0) { + return has_hex_prefix(str); + } + return false; +} +#else +bool should_be_skipped(const uint8_t *) { return false; } +#endif // LLVM_LIBC_ATOF_DIF_FUZZ_SKIP_GLIBC_HEX_SUBNORMAL_ERR + extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { uint8_t *container = new uint8_t[size + 1]; if (!container) @@ -26,7 +60,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { container[i] = data[i]; container[size] = '\0'; // Add null terminator to container. - StringParserOutputDiff<double>(&__llvm_libc::atof, &::atof, container, size); + if (!should_be_skipped(container)) { + StringParserOutputDiff<double>(&__llvm_libc::atof, &::atof, container, + size); + } delete[] container; return 0; } |