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

[via llvm-commits]

https://github.com/michaelrj-google created https://github.com/llvm/llvm-project/pull/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.


>From 786a06a0b8681e7449c84b0d349788c28a4737e1 Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Tue, 24 Oct 2023 10:28:07 -0700
Subject: [PATCH] [libc] Fix printf long double inf, bitcast in msan

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.
---
 libc/src/__support/CPP/CMakeLists.txt           |  5 ++++-
 libc/src/__support/CPP/bit.h                    |  2 ++
 .../stdio/printf_core/float_inf_nan_converter.h |  4 ++--
 libc/test/src/stdio/sprintf_test.cpp            | 17 ++++++++++++++++-
 .../bazel/llvm-project-overlay/libc/BUILD.bazel |  1 +
 5 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/libc/src/__support/CPP/CMakeLists.txt b/libc/src/__support/CPP/CMakeLists.txt
index a2d3bd7df9e9069..6853bfa3b304a34 100644
--- a/libc/src/__support/CPP/CMakeLists.txt
+++ b/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(
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 456266626ae9b20..f6f3131c1ccfd81 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/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
diff --git a/libc/src/stdio/printf_core/float_inf_nan_converter.h b/libc/src/stdio/printf_core/float_inf_nan_converter.h
index 3c24c393b354834..27a034cdcab1b72 100644
--- a/libc/src/stdio/printf_core/float_inf_nan_converter.h
+++ b/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;
diff --git a/libc/test/src/stdio/sprintf_test.cpp b/libc/test/src/stdio/sprintf_test.cpp
index f3d5dd698cbea44..5aa346c414b1fe1 100644
--- a/libc/test/src/stdio/sprintf_test.cpp
+++ b/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
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index fdf60cd0df89c28..3ae68193dccd2b2 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/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",
     ],
 )