[PATCH] PR libstdc++/79190 add fallback aligned_alloc implementation

[Jonathan Wakely]

This provides a definition of aligned_alloc for targets which have
none of aligned_alloc, posix_memalign, memalign or _aligned_alloc.

The code is based on gcc/config/i386/gmm_malloc.h but modified to only
use sizeof(void*) not 2*sizeof(void*), because I don't understand why
that's used in gmm_malloc.h, or what the comment means.

libstdc++-v3:

	PR libstdc++/79190
	* libsupc++/del_opa.cc (operator delete(void*, std::align_val_t))
	[!_GLIBCXX_HAVE_ALIGNED_ALLOC && !_GLIBCXX_HAVE_POSIX_MEMALIGN
	&& !_GLIBCXX_HAVE_MEMALIGN && !_GLIBCXX_HAVE__ALIGNED_MALLOC]:
	Retrieve original pointer value allocated by malloc.
	* libsupc++/new_opa.cc [!_GLIBCXX_HAVE_ALIGNED_ALLOC
	&& !_GLIBCXX_HAVE_POSIX_MEMALIGN && !_GLIBCXX_HAVE_MEMALIGN
	&& !_GLIBCXX_HAVE__ALIGNED_MALLOC] (aligned_alloc(size_t, size_t)):
	Define, adjusting pointer value allocated by malloc and storing for
	retrieval by operator delete.

gcc/testsuite:

	PR libstdc++/79190
	* g++.dg/cpp1z/aligned-new3.C: Replace operator new so behaviour
	matches replaced operator delete.

Tested powerpc64le-linux, and also tested after tweaking the
preprocessor checks so the new code was used.

If this works for HPUX I plan to commit it to trunk.


-------------- next part --------------
commit 2f17c7769b6917b6ab6884c87c4496e32d4cc057
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jan 24 16:17:15 2017 +0000

    PR libstdc++/79190 add fallback aligned_alloc implementation
    
    libstdc++-v3:
    
    	PR libstdc++/79190
    	* libsupc++/del_opa.cc (operator delete(void*, std::align_val_t))
    	[!_GLIBCXX_HAVE_ALIGNED_ALLOC && !_GLIBCXX_HAVE_POSIX_MEMALIGN
    	&& !_GLIBCXX_HAVE_MEMALIGN && !_GLIBCXX_HAVE__ALIGNED_MALLOC]:
    	Retrieve original pointer value allocated by malloc.
    	* libsupc++/new_opa.cc [!_GLIBCXX_HAVE_ALIGNED_ALLOC
    	&& !_GLIBCXX_HAVE_POSIX_MEMALIGN && !_GLIBCXX_HAVE_MEMALIGN
    	&& !_GLIBCXX_HAVE__ALIGNED_MALLOC] (aligned_alloc(size_t, size_t)):
    	Define, adjusting pointer value allocated by malloc and storing for
    	retrieval by operator delete.
    
    gcc/testsuite:
    
    	PR libstdc++/79190
    	* g++.dg/cpp1z/aligned-new3.C: Replace operator new so behaviour
    	matches replaced operator delete.

diff --git a/gcc/testsuite/g++.dg/cpp1z/aligned-new3.C b/gcc/testsuite/g++.dg/cpp1z/aligned-new3.C
index 73e3343..e50e62c 100644
--- a/gcc/testsuite/g++.dg/cpp1z/aligned-new3.C
+++ b/gcc/testsuite/g++.dg/cpp1z/aligned-new3.C
@@ -7,6 +7,11 @@ struct alignas(64) A {
   int i;
 };
 
+void* operator new (std::size_t n, std::align_val_t)
+{
+  return operator new (n);
+}
+
 bool deleted = false;
 void operator delete (void *p, std::size_t, std::align_val_t)
 {
diff --git a/libstdc++-v3/libsupc++/del_opa.cc b/libstdc++-v3/libsupc++/del_opa.cc
index c9afb46..f7bf7a4 100644
--- a/libstdc++-v3/libsupc++/del_opa.cc
+++ b/libstdc++-v3/libsupc++/del_opa.cc
@@ -46,9 +46,13 @@ _GLIBCXX_END_NAMESPACE_VERSION
 _GLIBCXX_WEAK_DEFINITION void
 operator delete(void* ptr, std::align_val_t) _GLIBCXX_USE_NOEXCEPT
 {
-#if !_GLIBCXX_HAVE_ALIGNED_ALLOC && _GLIBCXX_HAVE__ALIGNED_MALLOC
+#if _GLIBCXX_HAVE_ALIGNED_ALLOC || _GLIBCXX_HAVE_POSIX_MEMALIGN \
+    || _GLIBCXX_HAVE_MEMALIGN
+  std::free (ptr);
+#elif _GLIBCXX_HAVE__ALIGNED_MALLOC
   _aligned_free (ptr);
 #else
-  std::free(ptr);
+  if (ptr)
+    std::free (((void **) ptr)[-1]); // See aligned_alloc in new_opa.cc
 #endif
 }
diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 0bc2b5f..5d6c185 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -55,9 +55,30 @@ extern "C" void *memalign(std::size_t boundary, std::size_t size);
 #endif
 #define aligned_alloc memalign
 #else
-// The C library doesn't provide any aligned allocation functions, declare
-// aligned_alloc and get a link failure if aligned new is used.
-extern "C" void *aligned_alloc(std::size_t, std::size_t);
+// This is a modified version of code from gcc/config/i386/gmm_malloc.h
+static inline void*
+aligned_alloc (std::size_t al, std::size_t sz)
+{
+  // Alignment must be a power of two.
+  if (al & (al - 1))
+    return nullptr;
+  else if (!sz)
+    return nullptr;
+
+  // We need extra bytes to store the original value returned by malloc.
+  if (al < sizeof(void*))
+    al = sizeof(void*);
+  void* const malloc_ptr = malloc(sz + al);
+  if (!malloc_ptr)
+    return nullptr;
+  // Align to the requested value, leaving room for the original malloc value.
+  void* const aligned_ptr = (void *) (((size_t) malloc_ptr + al) & -al);
+
+  // Store the original malloc value where it can be found by operator delete.
+  ((void **) aligned_ptr)[-1] = malloc_ptr;
+
+  return aligned_ptr;
+}
 #endif
 #endif