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libstdc++: Prefer posix_memalign for aligned-new [PR113258]

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As described in PR libstdc++/113258 there are old versions of tcmalloc
which replace malloc and related APIs, but do not repalce aligned_alloc
because it didn't exist at the time they were released. This means that
when operator new(size_t, align_val_t) uses aligned_alloc to obtain
memory, it comes from libc's aligned_alloc not from tcmalloc. But when
operator delete(void*, size_t, align_val_t) uses free to deallocate the
memory, that goes to tcmalloc's replacement version of free, which
doesn't know how to free it.

If we give preference to the older posix_memalign instead of
aligned_alloc then we're more likely to use a function that will be
compatible with the replacement version of free. Because posix_memalign
has been around for longer, it's more likely that old third-party malloc
replacements will also replace posix_memalign alongside malloc and free.

libstdc++-v3/ChangeLog:

	PR libstdc++/113258
	* libsupc++/new_opa.cc: Prefer to use posix_memalign if
	available.
This commit is contained in:
Jonathan Wakely
2024-01-09 15:22:46 +00:00
parent 8f67953d01
commit f50f2efae9
1 changed files with 15 additions and 11 deletions
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26
libstdc++-v3/libsupc++/new_opa.cc
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@@ -46,12 +46,12 @@ using std::bad_alloc;
using std::size_t;
extern "C"
{
# if _GLIBCXX_HAVE_ALIGNED_ALLOC
# if _GLIBCXX_HAVE_POSIX_MEMALIGN
void *posix_memalign(void **, size_t alignment, size_t size);
# elif _GLIBCXX_HAVE_ALIGNED_ALLOC
void *aligned_alloc(size_t alignment, size_t size);
# elif _GLIBCXX_HAVE__ALIGNED_MALLOC
void *_aligned_malloc(size_t size, size_t alignment);
# elif _GLIBCXX_HAVE_POSIX_MEMALIGN
void *posix_memalign(void **, size_t alignment, size_t size);
# elif _GLIBCXX_HAVE_MEMALIGN
void *memalign(size_t alignment, size_t size);
# else
@@ -63,13 +63,10 @@ extern "C"
#endif
namespace __gnu_cxx {
#if _GLIBCXX_HAVE_ALIGNED_ALLOC
using ::aligned_alloc;
#elif _GLIBCXX_HAVE__ALIGNED_MALLOC
static inline void*
aligned_alloc (std::size_t al, std::size_t sz)
{ return _aligned_malloc(sz, al); }
#elif _GLIBCXX_HAVE_POSIX_MEMALIGN
// Prefer posix_memalign if available, because it's older than aligned_alloc
// and so more likely to be provided by replacement malloc libraries that
// predate the addition of aligned_alloc. See PR libstdc++/113258.
#if _GLIBCXX_HAVE_POSIX_MEMALIGN
static inline void*
aligned_alloc (std::size_t al, std::size_t sz)
{
@@ -83,6 +80,12 @@ aligned_alloc (std::size_t al, std::size_t sz)
return ptr;
return nullptr;
}
#elif _GLIBCXX_HAVE_ALIGNED_ALLOC
using ::aligned_alloc;
#elif _GLIBCXX_HAVE__ALIGNED_MALLOC
static inline void*
aligned_alloc (std::size_t al, std::size_t sz)
{ return _aligned_malloc(sz, al); }
#elif _GLIBCXX_HAVE_MEMALIGN
static inline void*
aligned_alloc (std::size_t al, std::size_t sz)
@@ -128,7 +131,8 @@ operator new (std::size_t sz, std::align_val_t al)
if (__builtin_expect (sz == 0, false))
sz = 1;
#if _GLIBCXX_HAVE_ALIGNED_ALLOC
#if _GLIBCXX_HAVE_POSIX_MEMALIGN
#elif _GLIBCXX_HAVE_ALIGNED_ALLOC
# if defined _AIX || defined __APPLE__
/* AIX 7.2.0.0 aligned_alloc incorrectly has posix_memalign's requirement
* that alignment is a multiple of sizeof(void*).