gperftools 2.11rc is out!

[Aliaksey Kandratsenka]

Hi all. I've just tagged release candidate (formally, 2.10.80) for upcoming 2.11 release.

I strongly encourage people to build & test this. And whoever has time, I would be really thankful to have extra pairs of eyes eyeballing those dozens of recent commits.

Please find the NEWS update below (and have a nice day).

Most notable change is that Linux/aarch64 and Linux/riscv are now fully supported. That is, all unit tests pass on those architectures (previously the heap leak checker was broken).

Also notable is that heap leak checker support is officially deprecated as of this release. All bug fixes from now are on a best effort basis. For clarity we also declare that it is only expected to work (for some definition of work) on Linux/x86 (all kinds), Linux/aarch64, Linux/arm, Linux/ppc (untested as of this writing) and Linux/mips (untested as well). While some functionality worked in the past on BSDs, it was never fully functional; and will never be. We strongly recommend everyone to switch to asan and friends.

For major internal changes it is also worth mentioning that we now fully switched to C++-11 std::atomic. All custom OS- and arch-specific atomic bits have been removed at last.

Another notable change is that mmap and sbrk hooks facility is now no-op. We keep API and ABI for formal compatibility, but the calls to add mmap/sbrk hooks do nothing and return an error (whenever possible as part of API). There seem to be no users of it anyways, and mmap replacement API that is part of that facility really screwed up 64-bit offsets on (some/most) 32-bit systems. Internally for heap profiler and heap checker we have a new, but non-public API (see mmap_hook.h).

Most tests now pass on NetBSD x86-64 (I tested on version 9.2). And only one that fails is new stacktrace test for stacktraces from signal handler (so there could be some imperfections for cpu profiles).

We don't warn people away from the libgcc stacktrace capturing method anymore. In fact users on most recent glibc-s are advised to use it (pass --enable-libgcc-unwinder-by-default). This is thanks to the dl_find_object API offered by glibc which allows this implementation to be fully async-signal-safe. Modern Linux distros should from now on build their gperftools package with this enabled (other than those built on top of musl).

generic_fp and generic_fp_unsafe stacktrace capturing methods have been expanded for more architectures and even some basic non-Linux support. We have completely removed old x86-specific frame pointer stacktrace implementation in favor of those 2. _unsafe one should be roughly equivalent to the old x86 method. And 'safe' one is recommended as a new default for those who want FP-based stacktracing. Safe implementation robustly checks memory before accessing it, preventing unlikely, but not impossible crashes when frame pointers are bogus.

On platforms that support it, we now build gperftools with "-fno-omit-frame-pointer -momit-leaf-frame-pointer". This makes gperftools mostly frame-pointer-ful, but without performance hit in places that matter (this is how Google builds their binaries BTW). That should cover gcc (at least) on x86, aarch64 and riscv. Intention for this change is to make distro-shipped libtcmalloc.so compatible with frame-pointer stacktrace capturing (for those who still do heap profiling, for example). Of course, passing --enable-frame-pointers still gives you full frame pointers (i.e. even for leaf functions).

There is now support for detecting actual page size at runtime. tcmalloc will now allocate memory in units of this page size. It particularly helps on arms with 64k pages to return memory back to the kernel. But it is somewhat controversial, because it effectively bumps tcmalloc logical page size on those machines potentially increasing fragmentation. In any case, there is now a new environment variable TCMALLOC_OVERRIDE_PAGESIZE allowing people to override this check. I.e. to either reduce effective page size down to tcmalloc's logical page size or to increase it.

MallocExtension::MarkThreadTemporarilyIdle has been changed to be identical to MarkThreadIdle. MarkThreadTemporarilyIdle is believed to be unused, anyways. See issue #880 for details.

There are a whole bunch of smaller fixes. Many of those smaller fixes had no associated ticket, but some had. People are advised to see here for a list of notable tickets closed in this release: https://github.com/gperftools/gperftools/issues?q=label%3Afixed-in-2.11+

Some of those tickets are quite notable (fixes for rare deadlocks in cpu profiler ProfilerStop or while capturing heap growth stacktraces (aka growthz)).

Here is list of notable contributions:

* Chris Cambly has contributed initial support for AIX

* Ali Saidi has contributed SpinlockPause implementation for aarch64

* Henrik Reinstädtler has contributed fix for cpuprofiler on aarch64 OSX

* Gabriel Marin has backported Chromium's commit for always sanity checking large frees

* User zhangyiru has contributed a fix to report the number of leaked bytes as size_t instead of (usually 32-bit) int.

* Sergey Fedorov has contributed some fix for building on older ppc-based OSX-es

* User tigeran has removed unused using declaration

Huge thanks to all contributors.