this patch improves the correctness, simplicity, and size of
cancellation-related code. modulo any small errors, it should now be
completely conformant, safe, and resource-leak free.
the notion of entering and exiting cancellation-point context has been
completely eliminated and replaced with alternative syscall assembly
code for cancellable syscalls. the assembly is responsible for setting
up execution context information (stack pointer and address of the
syscall instruction) which the cancellation signal handler can use to
determine whether the interrupted code was in a cancellable state.
these changes eliminate race conditions in the previous generation of
cancellation handling code (whereby a cancellation request received
just prior to the syscall would not be processed, leaving the syscall
to block, potentially indefinitely), and remedy an issue where
non-cancellable syscalls made from signal handlers became cancellable
if the signal handler interrupted a cancellation point.
x86_64 asm is untested and may need a second try to get it right.
setting errno here is completely valid, but some programs, notably
busybox printf, assume that errno will not be set during output and
treat this as an error condition. in any case, skipping it slightly
reduces code size and saves time.
otherwise we cannot support an application's desire to use
asynchronous cancellation within the callback function. this change
also slightly debloats pthread_create.c.
we take advantage of the fact that unless self->cancelpt is 1,
cancellation cannot happen. so just increment it by 2 to temporarily
block cancellation. this drops pthread_create.o well under 1k.
with datagram sockets, depending on fprintf not to flush the output
early was very fragile; the new version simply uses a small fixed-size
buffer. it could be updated to dynamic-allocate large buffers if
needed, but i can't envision any admin being happy about finding
64kb-long lines in their syslog...
some of these definitions were just plain wrong, others based on
outdated ancient "non-64" versions of the kernel interface.
as much as possible has now been moved out of bits/*
these changes break abi (the old abi for these functions was wrong),
but since they were not working anyway it can hardly matter.
it should be noted that flock does not mix well with standard fcntl
locking, but nonetheless some applications will attempt to use flock
instead of fcntl if both exist. options to configure or small patches
may be needed. debian maintainers have plenty of experience with this
unfortunate situation...
after fork, we have a new process and the pid is equal to the tid of
the new main thread. there is no need to make two separate syscalls to
obtain the same number.
we can do this without violating the namespace now that they are
macros/inline functions rather than extern functions. the motivation
is that gcc was generating giant, slow, horrible code for the old
functions, and now generates a single byte-swapping instruction.
the basic idea is that the only things in alltypes.h should be types
that either vary from system to system (in practice, not just in
theoretical la-la land - this is the implementation so we choose what
constraints we want to impose on ports) or which are needed by
multiple system headers.
1. saved errno was not being restored, illegally clearing errno to 0.
2. no need to backup and save errno around free; it will not touch
except perhaps when the program has already invoked UB...
actually FLT_ROUNDS needs to expand to a static inline function that
obtains the current rounding mode and returns it, but that will be
added later with fenv.h stuff.
