[libc] Fix printf long double inf, bitcast in msan (llvm#70067)

These bugs were found with the new printf long double fuzzing. The long double inf vs nan bug was introduced when we changed to get_explicit_exponent. The bitcast msan issue hadn't come up previously, but isn't a real bug, just a poisoning confusion.

Author: michaelrj-google

libc/src/__support/CPP/CMakeLists.txt

@@ -15,7 +15,10 @@ add_header_library(
  HDRS
  bit.h
  DEPENDS
- libc.src.__support.macros.properties.compiler
+ .type_traits
+ libc.src.__support.macros.attributes
+ libc.src.__support.macros.config
+ libc.src.__support.macros.sanitizer
 )
 
 add_header_library(

libc/src/__support/CPP/bit.h

@@ -12,6 +12,7 @@
 #include "src/__support/CPP/type_traits.h"
 #include "src/__support/macros/attributes.h"
 #include "src/__support/macros/config.h" // LIBC_HAS_BUILTIN
+#include "src/__support/macros/sanitizer.h"
 
 namespace LIBC_NAMESPACE::cpp {
 
@@ -31,6 +32,7 @@ LIBC_INLINE constexpr To bit_cast(const From &from) {
  static_assert(cpp::is_trivially_copyable<To>::value &&
  cpp::is_trivially_copyable<From>::value,
  "Cannot bit-cast instances of non-trivially copyable classes.");
+ MSAN_UNPOISON(&from, sizeof(From));
 #if defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
  return __builtin_bit_cast(To, from);
 #else

libc/src/stdio/printf_core/float_inf_nan_converter.h

@@ -34,13 +34,13 @@ LIBC_INLINE int convert_inf_nan(Writer *writer, const FormatSection &to_conv) {
  fputil::FPBits<long double>::UIntType float_raw = to_conv.conv_val_raw;
  fputil::FPBits<long double> float_bits(float_raw);
  is_negative = float_bits.get_sign();
- mantissa = float_bits.get_explicit_mantissa();
+ mantissa = float_bits.get_mantissa();
  } else {
  fputil::FPBits<double>::UIntType float_raw =
  static_cast<fputil::FPBits<double>::UIntType>(to_conv.conv_val_raw);
  fputil::FPBits<double> float_bits(float_raw);
  is_negative = float_bits.get_sign();
- mantissa = float_bits.get_explicit_mantissa();
+ mantissa = float_bits.get_mantissa();
  }
 
  char sign_char = 0;

libc/test/src/stdio/sprintf_test.cpp

@@ -572,7 +572,6 @@ TEST_F(LlvmLibcSPrintfTest, FloatHexExpConv) {
  ForceRoundingMode r(RoundingMode::Nearest);
  double inf = LIBC_NAMESPACE::fputil::FPBits<double>::inf().get_val();
  double nan = LIBC_NAMESPACE::fputil::FPBits<double>::build_nan(1);
-
  written = LIBC_NAMESPACE::sprintf(buff, "%a", 1.0);
  ASSERT_STREQ_LEN(written, buff, "0x1p+0");
 
@@ -937,6 +936,10 @@ TEST_F(LlvmLibcSPrintfTest, FloatDecimalConv) {
  ForceRoundingMode r(RoundingMode::Nearest);
  double inf = LIBC_NAMESPACE::fputil::FPBits<double>::inf().get_val();
  double nan = LIBC_NAMESPACE::fputil::FPBits<double>::build_nan(1);
+ long double ld_inf =
+ LIBC_NAMESPACE::fputil::FPBits<long double>::inf().get_val();
+ long double ld_nan =
+ LIBC_NAMESPACE::fputil::FPBits<long double>::build_nan(1);
 
  char big_buff[10000]; // Used for long doubles and other extremely wide
  // numbers.
@@ -996,6 +999,18 @@ TEST_F(LlvmLibcSPrintfTest, FloatDecimalConv) {
  written = LIBC_NAMESPACE::sprintf(buff, "%F", -nan);
  ASSERT_STREQ_LEN(written, buff, "-NAN");
 
+ written = LIBC_NAMESPACE::sprintf(buff, "%Lf", ld_inf);
+ ASSERT_STREQ_LEN(written, buff, "inf");
+
+ written = LIBC_NAMESPACE::sprintf(buff, "%LF", -ld_inf);
+ ASSERT_STREQ_LEN(written, buff, "-INF");
+
+ written = LIBC_NAMESPACE::sprintf(buff, "%Lf", ld_nan);
+ ASSERT_STREQ_LEN(written, buff, "nan");
+
+ written = LIBC_NAMESPACE::sprintf(buff, "%LF", -ld_nan);
+ ASSERT_STREQ_LEN(written, buff, "-NAN");
+
  // Length Modifier Tests.
 
  // TODO(michaelrj): Add tests for LONG_DOUBLE_IS_DOUBLE and 128 bit long

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -170,6 +170,7 @@ libc_support_library(
  ":__support_cpp_type_traits",
  ":__support_macros_attributes",
  ":__support_macros_config",
+ ":__support_macros_sanitizer",
  ":libc_root",
  ],
 )