Directly call _int_free_chunk during tcache shutdown to avoid recursion.
Calling __libc_free on a block from tcache gets flagged as a double free,
and tcache_double_free_verify checks every tcache chunk (quadratic
overhead).

Reviewed-by: Arjun Shankar <arjun@redhat.com>

Signed-off-by: Justin King <jcking@google.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

clang warns that this function is not used.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

The tcache is used for allocation only if an exact match is found. In the
large tcache code added in commit cbfd7988107b, we currently extract a
chunk of size greater than or equal to the size we need, but don't check
strict equality. This patch fixes that behaviour.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

Avoid needing to check for tcache == NULL by initializing it
to a dummy read-only tcache structure.  This dummy is all zeros,
so logically it is both full (when you want to put) and empty (when
you want to get).  Also, there are two dummies, one used for
"not yet initialized" and one for "tunables say we shouldn't have
a tcache".

The net result is twofold:

1. Checks for tcache == NULL may be removed from the fast path.
    Whether this makes the fast path faster when tcache is
    disabled is TBD, but the normal case is tcache enabled.

2. no memory for tcache is allocated if tunables disable caching.

Co-authored-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

clang does not support the __builtin_*_overflow_p builtins, on gcc
the macros will call __builtin_*_overflow_p.

Reviewed-by: Collin Funk <collin.funk1@gmail.com>

Cleanup _int_memalign. Simplify the logic. Add a seperate check
for mmap. Only release the tail chunk if it is at least MINSIZE.
Use the new mmap abstractions.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Linux handles virtual memory in Virtual Memory Areas (VMAs). The
madvise(MADV_HUGEPAGE) call works on a VMA granularity, which sets the
VM_HUGEPAGE flag on the VMA. If this VMA or a portion of it is mremapped
to a different location, Linux will create a new VMA, which will have
the same flags as the old one. This implies that the VM_HUGEPAGE flag
will be retained. Therefore, if we can guarantee that the old VMA was
marked with VM_HUGEPAGE, then there is no need to call madvise_thp() in
mremap_chunk().

The old chunk comes from a heap or non-heap allocation, both of which
have already been enlightened for THP. This implies that, if THP is on,
and the size of the old chunk is greater than or equal to thp_pagesize,
the VMA to which this chunk belongs to, has the VM_HUGEPAGE flag set.
Hence in this case we can avoid invoking the madvise() syscall.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Add mmap_set_chunk() to create a new chunk from an mmap block.
Remove set_mmap_is_hp() since it is done inside mmap_set_chunk().
Rename prev_size_mmap() to mmap_base_offset().  Cleanup comments.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Refactor malloc.c to remove dead code, create macros to abstract duplicated
code, and cleanup sysmalloc_mmap_fallback to remove logic not related to the
mmap call.

Change the return type of mmap_base to uintptr_t since this allows using
operations on the return value, and avoids casting in both calls in
mremap_chunk and munmap_chunk.

Cleanup sysmalloc_mmap_fallback. Remove unused parameters nb, oldsize
and av. Remove redundant overflow check and instead use size_t for all
parameters except extra_flags to prevent overflows. Move logic not concerned
with the mmap call itself outside the function after both calls to
sysmalloc_mmap_fallback are made; this means move code for naming the VMA
and marking the arena being extended as non-contiguous to the calling code to
be handled in the case that the mmap is successful. Calculate the fallback
size from nb to avoid modifying size after it has been set for MORECORE.

Remove unused noncontiguous macro.

Remove redundant assert for checking unreachable option for global_max_fast.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>