As part of cpu profiler we're extracting current PC (program counter)
of out signal's ucontext. Different OS and hardware combinations have
different ways for that. We had a list of variants that we tested at
compile time and populated PC_FROM_UCONTEXT macro into config.h. It
caused duplication and occasional mismatches between our autoconf and
cmake bits.
So this commit changes testing to be compile-time. We remove
complexity from build system and add some to C++ source.
We use SFINAE to find which of those variants compile (and we silently
assume that 'compiles' implies 'works'; this is what config-time
testing did too). Occasionally we'll face situations where several
variants compile. And we couldn't handle this case in pure C++. So we
have a small Ruby program that generates chain of inheritance among
SFINAE-specialized class templates. This handles prioritization among
variants.
List of ucontext->pc extraction variants is mostly same. We dropped
super-obsolete (circa Linux kernel 2.0) arm variant. And NetBSD case
is now improved. We now use their nice architecture-independent macro
instead of x86-specific access.
It is kinda minor feature, and apparently we never had it working. But
is a nice to have. Allows our users to override malloc/free/etc while
still being able to link to us (for tc_malloc for example). With
broken weakening we had this use-case broken for static library
case. And it should now work.
In most practical terms, this expands "official" heap leak checker
support to Linux/arm64 and Linux/riscv (mips-en and legacy arm are
likely to work & pass tests too now).
The code is now explicitly Linux-only, without trying to pretend
otherwise. Main goal of this change is to finally amputate
linux_syscall_support.h, which we historically had trouble maintaining
well. Biggest challenge was around thread listing facility which uses
clone (ptrace explicitly fails between threads) and that causes
difficulties around parent and child tasks sharing
errno. linux_syscall_support stuff had special feature to "redirect"
errno accesses. But it caused us for more trouble. We switched to
regular syscalls, and errno stamping avoidance is now simply via
careful programming.
A number of other cleanups is made (such us thread finding codes in
procfs which clearly was built for some ages old and odd kernels).
sem_post/sem_wait synchronization was previously potentially prone to
deadlock (if parent died at bad time). We now use pipe pair for this
synchronization and it is fully robust.
Previously we blindly tried to use libunwind whenever header is
detected. Even if actually working libunwind library is missing. This
is now fixed, so we attempt to use libunwind when it actually works.
Somehow recent freebsd ships libunwind.h (which seems to belong to
llvm's implementation), but apparently without matching .so. So then building
and linking failed.
As part of that we also upgrade required autoconf version to 2.69
which is what I see in rhel/centos 7 and ubuntu 14.04. Both are old
enough. And, of course, .tar.gz releases still ship "packaged" configure,
so will work on older distros.
This fixes issue #1335.
Previously it only was respected on x86_64, but this days lots of modern
ABIs are without frame pointers by default (e.g. arm64 and riscv, and
even older mips).
