glibc 2.19 - asyn-signal safe TLS and ASan.

[Siddhesh Poyarekar]

On Thu, Jan 23, 2014 at 01:59:08PM -0800, Andrew Hunter wrote:
> FYI -- you could easily do the same thing with calls to
> signal_safe_memalign from libc as a stopgap.  (Well, we'd need to
> export the symbols from libc, like I wanted to in the first place.)

Or we could just add a thread-local flag that malloc looks at and if
set, short-circuits its way to mmap and have signal_safe_malloc use
it:

static __thread bool force_mmap;

void *
signal_safe_malloc (size_t sz)
{
  force_mmap = true;
  void *ret = malloc (sz);
  force_mmap = false;
  return ret;
}

void *
sysmalloc (size_t sz)
{
...
  if (__glibc_unlikely (force_mmap)
      || ((unsigned long) (nb) >= (unsigned long) (mp_.mmap_threshold)
          && (mp_.n_mmaps < mp_.n_mmaps_max)))
    {
    ...
      /* call mmap and just fail if force_mmap is set and mmap fails.
         Otherwise fall back to the heap as usual.  */
    ...
    }

...
}

Rinse and repeat for realloc, memalign, etc.  free would work out of
the box since the chunk_is_mmapped.

Siddhesh