originally, the comment in this code was correct and it would likely
work if the compiler generated a tail call to setjmp. however, commit
583e55122e redesigned sigsetjmp and
siglongjmp such that the old C implementation (which was not intended
to be used) is not even conceptually correct. remove it in the
interest of avoiding confusion when porting to new archs.
nominally the low bits of the trap number on sh are the number of
syscall arguments, but they have never been used by the kernel, and
some code making syscalls does not even know the number of arguments
and needs to pass an arbitrary high number anyway.
sh3/sh4 traditionally used the trap range 16-31 for syscalls, but part
of this range overlapped with hardware exceptions/interrupts on sh2
hardware, so an incompatible range 32-47 was chosen for sh2.
using trap number 31 everywhere, since it's in the existing sh3/sh4
range and does not conflict with sh2 hardware, is a proposed
unification of the kernel syscall convention that will allow binaries
to be shared between sh2 and sh3/sh4. if this is not accepted into the
kernel, we can refit the sh2 target with runtime selection mechanisms
for the trap number, but doing so would be invasive and would entail
non-trivial overhead.
the 64-bit push reads not only the 32-bit return address but also the
first 32 signal mask bits. if any were nonzero, the return address
obtained will be invalid.
at some point storage of the return address should probably be moved
to follow the saved mask so that there's plenty room and the same code
can be used on x32 and regular x86_64, but for now I want a fix that
does not risk breaking x86_64, and this simple re-zeroing works.
while the sh port is still experimental and subject to ABI
instability, this is not actually an application/libc boundary ABI
change. it only affects third-party APIs where jmp_buf is used in a
shared structure at the ABI boundary, because nothing anywhere near
the end of the jmp_buf object (which includes the oversized sigset_t)
is accessed by libc.
both glibc and uclibc have 15-slot jmp_buf for sh. presumably the
smaller version was used in musl because the slots for fpu status
register and thread pointer register (gbr) were incorrect and must not
be restored by longjmp, but the size should have been preserved, as
it's generally treated as a libc-agnostic ABI property for the arch,
and having extra slots free in case we ever need them for something is
useful anyway.
these are perfectly fine with ld-time symbol binding, but otherwise
result in textrels. they cannot be replaced with @PLT jump targets
because the PLT thunks require a GOT register to be setup, so use a
hidden alias instead.
these are perfectly fine with ld-time symbol binding, but if the calls
go through a PLT thunk, they are invalid because the caller does not
setup a GOT register. use a hidden alias to bypass the issue.
none of these are actual textrels because of ld-time binding performed
by -Bsymbolic-functions, but I'm changing them with the goal of making
ld-time binding purely an optimization rather than relying on it for
semantic purposes.
in the case of memmove's call to memcpy, making it explicit that the
memmove asm is assuming the forward-copying behavior of the memcpy asm
is desirable anyway; in case memcpy is ever changed, the semantic
mismatch would be apparent while editing memmcpy.s.
the conventional way to implement sigsetjmp is to save the signal mask
then tail-call to setjmp; siglongjmp then restores the signal mask and
calls longjmp. the problem with this approach is that a signal already
pending, or arriving between unmasking of signals and restoration of
the saved stack pointer, will have its signal handler run on the stack
that was active before siglongjmp was called. this can lead to
unbounded stack usage when siglongjmp is used to leave a signal
handler.
in the new design, sigsetjmp saves its own return address inside the
extended part of the sigjmp_buf (outside the __jmp_buf part used by
setjmp) then calls setjmp to save a jmp_buf inside its own execution.
it then tail-calls to __sigsetjmp_tail, which uses the return value of
setjmp to determine whether to save the current signal mask or restore
a previously-saved mask.
as an added bonus, this design makes it so that siglongjmp and longjmp
are identical. this is useful because the __longjmp_chk function we
need to add for ABI-compatibility assumes siglongjmp and longjmp are
the same, but for different reasons -- it was designed assuming either
can access a flag just past the __jmp_buf indicating whether the
signal masked was saved, and act on that flag. however, early versions
of musl did not have space past the __jmp_buf for the non-sigjmp_buf
version of jmp_buf, so our setjmp cannot store such a flag without
risking clobbering memory on (very) old binaries.
This adds complete aarch64 target support including bigendian subarch.
Some of the long double math functions are known to be broken otherwise
interfaces should be fully functional, but at this point consider this
port experimental.
Initial work on this port was done by Sireesh Tripurari and Kevin Bortis.
this shaves off a useless syscall for getting the caller's pid and
brings raise into alignment with other functions which were adapted to
use tkill rather than tgkill.
commit 83dc6eb087 documents the
rationale for this change, and in particular why the tgkill syscall is
useless for its designed purpose of avoiding races.
With the exception of a fenv implementation, the port is fully featured.
The port has been tested in or1ksim, the golden reference functional
simulator for OpenRISC 1000.
It passes all libc-test tests (except the math tests that
requires a fenv implementation).
The port assumes an or1k implementation that has support for
atomic instructions (l.lwa/l.swa).
Although it passes all the libc-test tests, the port is still
in an experimental state, and has yet experienced very little
'real-world' use.
it should be noted that the "real" __sysv_signal, which we do not
implement, is semantically different from signal. references to
__sysv_signal arise in code built against glibc under certain
combinations of feature test macros, and are almost surely
unintentional since the legacy sysv signal behavior has fundamental
race conditions that cannot be worked around and which make it
impossible to use safely.
this is the first step in an overhaul aimed at greatly simplifying and
optimizing everything dealing with thread-local state.
previously, the thread pointer was initialized lazily on first access,
or at program startup if stack protector was in use, or at certain
random places where inconsistent state could be reached if it were not
initialized early. while believed to be fully correct, the logic was
fragile and non-obvious.
in the first phase of the thread pointer overhaul, support is retained
(and in some cases improved) for systems/situation where loading the
thread pointer fails, e.g. old kernels.
some notes on specific changes:
- the confusing use of libc.main_thread as an indicator that the
thread pointer is initialized is eliminated in favor of an explicit
has_thread_pointer predicate.
- sigaction no longer needs to ensure that the thread pointer is
initialized before installing a signal handler (this was needed to
prevent a situation where the signal handler caused the thread
pointer to be initialized and the subsequent sigreturn cleared it
again) but it still needs to ensure that implementation-internal
thread-related signals are not blocked.
- pthread tsd initialization for the main thread is deferred in a new
manner to minimize bloat in the static-linked __init_tp code.
- pthread_setcancelstate no longer needs special handling for the
situation before the thread pointer is initialized. it simply fails
on systems that cannot support a thread pointer, which are
non-conforming anyway.
- pthread_cleanup_push/pop now check for missing thread pointer and
nop themselves out in this case, so stdio no longer needs to avoid
the cancellable path when the thread pointer is not available.
a number of cases remain where certain interfaces may crash if the
system does not support a thread pointer. at this point, these should
be limited to pthread interfaces, and the number of such cases should
be fewer than before.
linux, gcc, etc. all use "sh" as the name for the superh arch. there
was already some inconsistency internally in musl: the dynamic linker
was searching for "ld-musl-sh.path" as its path file despite its own
name being "ld-musl-superh.so.1". there was some sentiment in both
directions as to how to resolve the inconsistency, but overall "sh"
was favored.
this change is consistent with the corresponding glibc functions and
is semantically const-correct. the incorrect argument types without
const seem to have been taken from erroneous man pages.
commit 07827d1a82 seems to have
introduced this issue. sigqueue is called from the synccall core, at
which time, even implementation-internal signals are blocked. however,
pthread_sigmask removes the implementation-internal signals from the
old mask before returning, so that a process which began life with
them blocked will not be able to save a signal mask that has them
blocked, possibly causing them to become re-blocked later. however,
this was causing sigqueue to unblock the implementation-internal
signals during synccall, leading to deadlock.
a mips signal mask contains 128 bits, enough for signals 1 through
128. however, the exit status obtained from the wait-family functions
only has room for values up to 127. reportedly signal 128 was causing
kernelspace bugs, so it was removed from the kernel recently; even
without that issue, however, it was impossible to support it correctly
in userspace.
at the same time, the bug was masked on musl by SIGRTMAX incorrectly
yielding 64 on mips, rather than the "correct" value of 128. now that
the _NSIG issue is fixed, SIGRTMAX can be fixed at the same time,
exposing the full range of signals for application use.
note that the (nonstandardized) libc _NSIG value is actually one
greater than the max signal number, and also one greater than the
kernel headers' idea of _NSIG. this is the reason for the discrepency
with the recent kernel changes. since reducing _NSIG by one brought it
down from 129 to 128, rather than from 128 to 127, _NSIG/8, used
widely in the musl sources, is unchanged.
the idea here is to avoid advertising signals that don't exist and to
make these functions safe to call (e.g. from within other parts of the
implementation) on fake sigset_t objects which do not have the HURD
padding.
the trick here is that sigaction can track for us which signals have
ever had a signal handler set for them, and only those signals need to
be considered for reset. this tracking mask may have false positives,
since it is impossible to remove bits from it without race conditions.
false negatives are not possible since the mask is updated with atomic
operations prior to making the sigaction syscall.
implementation-internal signals are set to SIG_IGN rather than SIG_DFL
so that a signal raised in the parent (e.g. calling pthread_cancel on
the thread executing pthread_spawn) does not have any chance make it
to the child, where it would cause spurious termination by signal.
this change reduces the minimum/typical number of syscalls in the
child from around 70 to 4 (including execve). this should greatly
improve the performance of posix_spawn and other interfaces which use
it (popen and system).
to facilitate these changes, sigismember is also changed to return 0
rather than -1 for invalid signals, and to return the actual status of
implementation-internal signals. POSIX allows but does not require an
error on invalid signal numbers, and in fact returning an error tends
to confuse applications which wrongly assume the return value of
sigismember is boolean.
in signal() it is needed since __sigaction uses restrict in parameters
and sharing the buffer is technically an aliasing error. do the same
for the syscall, as at least qemu-user does not handle it properly.
this is necessary to meet the C++ ABI target. alternatives were
considered to avoid the size increase for non-sig jmp_buf objects, but
they seemed to have worse properties. moreover, the relative size
increase is only extreme on x86[_64]; one way of interpreting this is
that, if the size increase from this patch makes jmp_buf use too much
memory, then the program was already using too much memory when built
for non-x86 archs.
there are several reasons for this change. one is getting rid of the
repetition of the syscall signature all over the place. another is
sharing the constant masks without costly GOT accesses in PIC.
the main motivation, however, is accurately representing whether we
want to block signals that might be handled by the application, or all
signals.
the issue at hand is that many syscalls require as an argument the
kernel-ABI size of sigset_t, intended to allow the kernel to switch to
a larger sigset_t in the future. previously, each arch was defining
this size in syscall_arch.h, which was redundant with the definition
of _NSIG in bits/signal.h. as it's used in some not-quite-portable
application code as well, _NSIG is much more likely to be recognized
and understood immediately by someone reading the code, and it's also
shorter and less cluttered.
note that _NSIG is actually 65/129, not 64/128, but the division takes
care of throwing away the off-by-one part.
it's essential to decrement the stack pointer before writing to new
stack space, rather than afterwards. otherwise there is a race
condition during which asynchronous code (signals) could clobber the
data being stored.
it may be possible to optimize the code further using stwu, but I
wanted to avoid making any changes to the actual stack layout in this
commit. further improvements can be made separately if desired.
this mirrors the stdio_impl.h cleanup. one header which is not
strictly needed, errno.h, is left in pthread_impl.h, because since
pthread functions return their error codes rather than using errno,
nearly every single pthread function needs the errno constants.
in a few places, rather than bringing in string.h to use memset, the
memset was replaced by direct assignment. this seems to generate much
better code anyway, and makes many functions which were previously
non-leaf functions into leaf functions (possibly eliminating a great
deal of bloat on some platforms where non-leaf functions require ugly
prologue and/or epilogue).
Rich Felker
Szabolcs Nagy
Stefan Kristiansson
Bobby Bingham
rofl0r
Timo Teräs
Richard Pennington