Use posix_memalign on all POSIX platforms

Summary:
The feature detection seems to be incorrect, resulting in fallback to the
manual implementation, which in turn returns untagged pointers under hwasan.

Replace the feature detection with a check on `_POSIX_VERSION` and use
`posix_memalign` which is available on quite old platforms as well.

Remove rounding shenanigans while I'm here; the documentation on
ET_ALIGNED_ALLOC already stipulates that the caller is responsible for such
rounding.

Differential Revision: D75806635

Author: Tamir Duberstein

extension/data_loader/file_descriptor_data_loader.cpp

@@ -164,9 +164,10 @@ Result<FreeableBuffer> FileDescriptorDataLoader::load(
   if (aligned_buffer == nullptr) {
     ET_LOG(
         Error,
-        "Reading from %s at offset %zu: ET_ALIGNED_ALLOC(%zd) failed",
+        "Reading from %s at offset %zu: ET_ALIGNED_ALLOC(%zd, %zd) failed",
         file_descriptor_uri_,
         offset,
+        alignment_,
         size);
     return Error::MemoryAllocationFailed;
   }

runtime/platform/compiler.h

@@ -183,36 +183,31 @@ using ssize_t = ptrdiff_t;
  * alignment.
  */
 #if defined(_MSC_VER)
-#include <malloc.h>
+#include <cstdlib> // For _aligned_malloc and _aligned_free
 #define ET_ALIGNED_ALLOC(alignment, size) \
-  _aligned_malloc(((size + alignment - 1) & ~(alignment - 1)), (alignment))
+  _aligned_malloc((size), (alignment))
 #define ET_ALIGNED_FREE(ptr) _aligned_free(ptr)
-#elif defined(__APPLE__)
-#include <stdlib.h> // For posix_memalign and free
-inline void* et_apple_aligned_alloc(size_t alignment, size_t size) {
+#else
+#include <unistd.h> // For _POSIX_VERSION
+#if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 200112L)
+#include <cstdlib> // For posix_memalign and free
+inline void* et_posix_aligned_alloc(size_t alignment, size_t size) {
   void* ptr = nullptr;
   // The address of the allocated memory must be a multiple of sizeof(void*).
   if (alignment < sizeof(void*)) {
     alignment = sizeof(void*);
   }
-  if (posix_memalign(
-          &ptr, alignment, (size + alignment - 1) & ~(alignment - 1)) != 0) {
+  if (posix_memalign(&ptr, alignment, size) != 0) {
     return nullptr;
   }
   return ptr;
 }
 #define ET_ALIGNED_ALLOC(alignment, size) \
-  et_apple_aligned_alloc((alignment), (size))
-#define ET_ALIGNED_FREE(ptr) free(ptr)
-#elif __has_builtin(__builtin_aligned_alloc) || defined(_ISOC11_SOURCE)
-// Linux and posix systems that support aligned_alloc and are >= C++17.
-#include <cstdlib>
-#define ET_ALIGNED_ALLOC(alignment, size) \
-  ::aligned_alloc(alignment, (size + alignment - 1) & ~(alignment - 1))
+  et_posix_aligned_alloc((alignment), (size))
 #define ET_ALIGNED_FREE(ptr) free(ptr)
 #else
-// If the platform doesn't support aligned_alloc, fallback to malloc.
-#include <stdint.h>
+// If the platform doesn't support posix_memalign, fallback to malloc.
+#include <cstdint>
 #include <cstdlib>
 inline void* et_aligned_malloc(size_t alignment, size_t size) {
   // Place to store the offset to the original pointer.
@@ -263,7 +258,7 @@ inline void et_aligned_free(void* ptr) {
 
 #define ET_ALIGNED_ALLOC(alignment, size) et_aligned_malloc((alignment), (size))
 #define ET_ALIGNED_FREE(ptr) et_aligned_free(ptr)
-
+#endif
 #endif
 
 // DEPRECATED: Use the non-underscore-prefixed versions instead.