Commits on Dec 14, 2023

1. [libc] fix msan failure in mempcpy_test …

   Internal builds of the unittests with msan flagged mempcpy_test.
   
       ==6862==WARNING: MemorySanitizer: use-of-uninitialized-value
       #0 0x55e34d7d734a in length llvm-project/libc/src/__support/CPP/string_view.h:41:11
       llvm#1 0x55e34d7d734a in string_view llvm-project/libc/src/__support/CPP/string_view.h:71:24
       llvm#2 0x55e34d7d734a in __llvm_libc_9999_0_0_git::testing::Test::testStrEq(char const*, char const*, char const*, char const*, __llvm_libc_9999_0_0_git::testing::internal::Location) llvm-project/libc/test/UnitTest/LibcTest.cpp:284:13
       llvm#3 0x55e34d7d4e09 in LlvmLibcMempcpyTest_Simple::Run() llvm-project/libc/test/src/string/mempcpy_test.cpp:20:3
       llvm#4 0x55e34d7d6dff in __llvm_libc_9999_0_0_git::testing::Test::runTests(char const*) llvm-project/libc/test/UnitTest/LibcTest.cpp:133:8
       llvm#5 0x55e34d7d86e0 in main llvm-project/libc/test/UnitTest/LibcTestMain.cpp:21:10
   
       SUMMARY: MemorySanitizer: use-of-uninitialized-value llvm-project/libc/src/__support/CPP/string_view.h:41:11 in length
   
   What's going on here is that mempcpy_test.cpp's Simple test is using
   ASSERT_STREQ with a partially initialized char array. ASSERT_STREQ calls
   Test::testStrEq which constructs a cpp:string_view. That constructor calls the
   private method cpp::string_view::length. When built with msan, the loop is
   transformed into multi-byte access, which then fails upon access.
   
   I took a look at libc++'s __constexpr_strlen which just calls
   __builtin_strlen().  Replacing the implementation of cpp::string_view::length
   with a call to __builtin_strlen() may still result in out of bounds access when
   the test is built with msan.
   
   It's not safe to use ASSERT_STREQ with a partially initialized array.
   Initialize the whole array so that the test passes.

   

   nickdesaulniers committed Dec 14, 2023
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