This fixes issue #1371
From time to time things file inside tcmalloc guts where calling to
malloc is not safe. Regular strerror does locale bits, so will
occasionally open files/malloc/etc. We avoid this by using our own
"safe" variant that hardcodes names of all POSIX errno constants.
We had plenty of old and mostly no more correct i386 cruft. Now that
generic_fp backtracer covers i386 just fine, we can drop explicit x86
backtracer.
With that we refactored and simplified stacktrace.cc mostly around
picking default implementation, but also adding few more minor
cleanups.
The idea is -momit-leaf-frame-pointer gives us performance pretty much
same as fully omitting frame pointers. And having frame pointers
elsewhere allows us to support cases when user's code is built with
frame pointers. We also pass all tests with
TCMALLOC_STACKTRACE_METHOD=generic_fp (not just libunwind or libgcc).
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.
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).
