Unfortunately, C still lacks a standard function for pause (x86,
sparc) or yeild (arm) instructions, for use in spin lock or CAS loops.
BIND has its own based on vendor intrinsics or inline asm.
Previously, it was buried in the `isc_rwlock` implementation. This
commit renames `isc_rwlock_pause()` to `isc_pause()` and moves
it into <isc/pause.h>.
This commit also fixes the configure script so that it detects ARM
yield support on systems that identify as `aarch*` instead of `arm*`.
On 64-bit ARM systems we now use the ISB (instruction synchronization
barrier) instruction in preference to yield. The ISB instruction
pauses the CPU for longer, several nanoseconds, which is more like the
x86 pause instruction. There are more details in a Rust pull request,
which also refers to MySQL making the same change:
https://github.com/rust-lang/rust/pull/84725
* rbt node chains were sized to allow for bitstring labels, so they
had 256 levels; but in the absence of bistrings, 128 is enough.
* dns_byaddr_createptrname() had a redundant options argument,
and a very outdated doc comment.
* A number of comments referred to bitstring labels in a way that is
no longer helpful. (A few informative comments remain.)
ISC_MEM_ZERO requires great care to use when the space returned by
the allocator is larger than the requested space, and when memory is
reallocated. You must ensure that _every_ call to allocate or
reallocate a particular block of memory uses ISC_MEM_ZERO, to ensure
that the extra space is zeroed as expected. (When ISC_MEMFLAG_FILL
is set, the extra space will definitely be non-zero.)
When BIND is built without jemalloc, ISC_MEM_ZERO is implemented in
`jemalloc_shim.h`. This had a bug on systems that have malloc_size()
or malloc_usable_size(): memory was only zeroed up to the requested
size, not the allocated size. When an oversized allocation was
returned, and subsequently reallocated larger, memory between the
original requested size and the original allocated size could
contain unexpected nonzero junk. The realloc call does not know the
original requested size and only zeroes from the original allocated
size onwards.
After this change, `jemalloc_shim.h` always zeroes up to the
allocated size, not the requested size.
This bug was masked in the tests because the `catz` test script did an
`rndc addzone` before an `rndc delzone`. The `addzone` autovivified
the NZF config, so `delzone` worked OK.
This commit swaps the order of two sections of the `catz` test script
so that it uses `delzone` before `addzone`, which provokes a crash
when `delzone` requires a non-NULL NZF config.
To fix the crash, we now try to remove the zone from the NZF config
only if it was dynamically added but not by a catalog zone.
