[OpenMP][libomp] Remove false positive for memory sanitizer

[jlpeyton]

Summary

The memory sanitizer intercepts the memcpy() call but not the direct assignment of last byte to 0. This leads the sanitizer to believe the last byte of a string based on the kmp_str_buf_t type is uninitialized. Hence, the eventual strlen() inside __kmp_env_dump() leads to an use-of-uninitialized-value warning.

Using strncat() instead gives the sanitizer the information it needs.

Fixes #60501

[jhuber6]

LG, thanks for the fix.

[ronlieb]

Hi Jonathon,
our amdgpu buildbot seems to have been broken by this patch
https://lab.llvm.org/buildbot/#/builders/193/builds/26173
could you fix quickly? or revert and fix ?

locall reverting patch , resolves buildbot issue.

Ron

[ronlieb]

i reverted to unblock our bot

[jlpeyton]

Apologies for the breakage!

Update patch to consider that buf.used may be "downsized" without setting a null byte. Hence, buf.str + buf.used may not point to a null-byte. If we insert a null-byte forcefully for __kmp_str_buf_cat[buf]() then the strncat() works as expected as well as preventing false positives from the memory sanitizer.

openmp/runtime/src/kmp_safe_c_api.h

 // _malloca was suggested, but it is not a drop-in replacement for _alloca
 #define KMP_ALLOCA _alloca
 
 #define KMP_MEMCPY_S memcpy_s
 #define KMP_SNPRINTF sprintf_s
 #define KMP_SSCANF sscanf_s
 #define KMP_STRCPY_S strcpy_s
 #define KMP_STRNCPY_S strncpy_s
+#define KMP_STRNCAT_S strncat_s
 
 // Use this only when buffer size is unknown
 #define KMP_MEMCPY(dst, src, cnt) memcpy_s(dst, cnt, src, cnt)
 
 template <typename T, bool B = std::is_array<T>::value>
 struct kmp_get_rmax_t {};
 template <typename T> struct kmp_get_rmax_t<T, false> {
   static const size_t value = RSIZE_MAX_STR;

 // For now, these macros use the existing API.
 
 #define KMP_ALLOCA alloca
 #define KMP_MEMCPY_S(dst, bsz, src, cnt) memcpy(dst, src, cnt)
 #define KMP_SNPRINTF snprintf
 #define KMP_SSCANF sscanf
 #define KMP_STRCPY_S(dst, bsz, src) strcpy(dst, src)
 #define KMP_STRNCPY_S(dst, bsz, src, cnt) strncpy(dst, src, cnt)
+#define KMP_STRNCAT_S(dst, bsz, src, cnt) strncat(dst, src, cnt)
 #define KMP_VSNPRINTF vsnprintf
 #define KMP_STRNCPY strncpy
 #define KMP_STRLEN strlen
 #define KMP_MEMCPY memcpy
 
 #endif // KMP_OS_WINDOWS
 
 // Offer truncated version of strncpy

openmp/runtime/src/kmp_str.cpp

 } // __kmp_str_buf_free
 
 void __kmp_str_buf_cat(kmp_str_buf_t *buffer, char const *str, size_t len) {
   KMP_STR_BUF_INVARIANT(buffer);
   KMP_DEBUG_ASSERT(str != NULL);
   KMP_DEBUG_ASSERT(len >= 0);
 
   __kmp_str_buf_reserve(buffer, buffer->used + len + 1);
-  KMP_MEMCPY(buffer->str + buffer->used, str, len);
-  buffer->str[buffer->used + len] = 0;
+  buffer->str[buffer->used] = '\0';
+  KMP_STRNCAT_S(buffer->str + buffer->used, len + 1, str, len);
   __kmp_type_convert(buffer->used + len, &(buffer->used));
   KMP_STR_BUF_INVARIANT(buffer);
 } // __kmp_str_buf_cat
 
 void __kmp_str_buf_catbuf(kmp_str_buf_t *dest, const kmp_str_buf_t *src) {
   KMP_DEBUG_ASSERT(dest);
   KMP_DEBUG_ASSERT(src);
   KMP_STR_BUF_INVARIANT(dest);
   KMP_STR_BUF_INVARIANT(src);
   if (!src->str || !src->used)
     return;
   __kmp_str_buf_reserve(dest, dest->used + src->used + 1);
-  KMP_MEMCPY(dest->str + dest->used, src->str, src->used);
-  dest->str[dest->used + src->used] = 0;
+  dest->str[dest->used] = '\0';
+  KMP_STRNCAT_S(dest->str + dest->used, src->used + 1, src->str, src->used);
   dest->used += src->used;
   KMP_STR_BUF_INVARIANT(dest);
 } // __kmp_str_buf_catbuf
 
 // Return the number of characters written
 int __kmp_str_buf_vprint(kmp_str_buf_t *buffer, char const *format,
                          va_list args) {
   int rc;