[libc-commits] [PATCH] D149359: [libc] add exception to atof differential fuzz

[Michael Jones via Phabricator via libc-commits]

michaelrj updated this revision to Diff 517698.
michaelrj marked 2 inline comments as done.
michaelrj added a comment.

switch to system atof for exception detection.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149359/new/

https://reviews.llvm.org/D149359

Files:
  libc/fuzzing/stdlib/atof_differential_fuzz.cpp


Index: libc/fuzzing/stdlib/atof_differential_fuzz.cpp
===================================================================
--- libc/fuzzing/stdlib/atof_differential_fuzz.cpp
+++ libc/fuzzing/stdlib/atof_differential_fuzz.cpp
@@ -16,6 +16,41 @@
 
 #include "fuzzing/stdlib/StringParserOutputDiff.h"
 
+// TODO: Remove this once glibc fixes hex subnormal rounding. See
+// https://sourceware.org/bugzilla/show_bug.cgi?id=30220
+#define LLVM_LIBC_FUZZER_GLIBC_HEX_SUBNORMAL_ERR
+#ifdef LLVM_LIBC_FUZZER_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_FUZZER_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 +61,10 @@
     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;
 }


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