MFC r352456:
realloc(x, 0) should not return NULL.

PR: 240456

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Update jemalloc to 4.2.1.

Update jemalloc to 4.2.0.

Restore support for decay time of -1 (no decay).

Add a cast to prevent a compiler warning.

Update jemalloc to 4.1.0.

Add missing Symbol.map entry for __aligned_alloc.

Add weak-->strong symbol binding for
{malloc_stats_print,mallctl,mallctlnametomib,mallctlbymib} -->
{__malloc_stats_print,__mallctl,__mallctlnametomib,__mallctlbymib}. These
bindings complete the set necessary to allow applications to replace all
malloc-related symbols.

Update jemalloc to version 4.0.4.

Update jemalloc to 4.0.2.

Update jemalloc to version 4.0.0.

Fix known issues which blow up the process after dlopen("libthr.so")
(or loading a dso linked to libthr.so into process which was not
linked against threading library).

- Remove libthr interposers of the libc functions, including
__error(). Instead, functions calls are indirected through the
interposing table, similar to how pthread stubs in libc are already
done. Libc by default points either to syscall trampolines or to
existing libc implementations. On libthr load, libthr rewrites the
pointers to the cancellable implementations already in libthr. The
interposition table is separate from pthreads stubs indirection
table to not pull pthreads stubs into static binaries.

- Postpone the malloc(3) internal mutexes initialization until libthr
is loaded. This avoids recursion between calloc(3) and static
pthread_mutex_t initialization.

- Reinstall signal handlers with wrapper on libthr load. The
_rtld_is_dlopened(3) is used to avoid useless calls to sigaction(2)
when libthr is statically referenced from the main binary.

In the process, fix openat(2), swapcontext(2) and setcontext(2)
interposing. The libc symbols were exported at different versions
than libthr interposers. Export both libc and libthr versions from
libc now, with default set to the higher version from libthr.

Remove unused and disconnected swapcontext(3) userspace implementation
from libc/gen.

No objections from: deischen
Tested by: pho, antoine (exp-run) (previous versions)
Sponsored by: The FreeBSD Foundation
MFC after: 1 week

Update jemalloc to version 3.6.0.

Update jemalloc to version 3.5.1.

Update jemalloc to version 3.5.0.

Update jemalloc to version 3.4.1.

Update jemalloc to version 3.4.0.

Import jemalloc 3.3.0. This reduces zeroed memory validation overhead for
non-MALLOC_PRODUCTION builds.

Import jemalloc 3.2.0.

Import jemalloc 3.0.0. This fixes memory zeroing bugs that manifested as
jemalloc assertion failures for debug builds, or as calloc() sometimes
returning non-zeroed memory for production builds.

Import jemalloc 37b6f95dcd866f51c91488531a2efc3ed4c2b754 (dev branch,
prior to 3.0.0 release). This version is likely very close to what will be
3.0.0.

Work around llvm PR 12623, which makes variables declared with .symver
sometimes disappear from the resulting object file, if compiled with
clang. In particular, this can lead to errors when building world with
clang and -g, similar to:

/usr/obj/usr/src/tmp/usr/lib/libc.so: undefined reference to `_malloc_options'

Reported by: Conrad J. Sabatier <conrads@.no.cox.net>
Reviewed by: jasone

Import jemalloc a8f8d7540d66ddee7337db80c92890916e1063ca (dev branch,
prior to 3.0.0 release). This fixes several bugs related to memory
initialization.

Mangle __jemalloc_a0{malloc,calloc,free}() just like all the other
library-internal symbols in jemalloc, and adjust the tls allocation code
in libc to use the mangled names.

Import jemalloc 606f1fdc3cdbc700717133ca56685313caea24bb (dev branch,
prior to 3.0.0 release), and mangle internal symbols.

Import jemalloc 9ef7f5dc34ff02f50d401e41c8d9a4a928e7c2aa (dev branch,
prior to 3.0.0 release) as contrib/jemalloc, and integrate it into libc.
The code being imported by this commit diverged from
lib/libc/stdlib/malloc.c in March 2010, which means that a portion of
the jemalloc 1.0.0 ChangeLog entries are relevant, as are the entries
for all subsequent releases.