these syscalls are new in linux v3.17 and present on all supported
archs except sh.
seccomp was added in commit 48dc92b9fc3926844257316e75ba11eb5c742b2c
it has operation, flags and pointer arguments (if flags==0 then it is
the same as prctl(PR_SET_SECCOMP,...)), the uapi header for flag
definitions is linux/seccomp.h
getrandom was added in commit c6e9d6f38894798696f23c8084ca7edbf16ee895
it provides an entropy source when open("/dev/urandom",..) would fail,
the uapi header for flags is linux/random.h
memfd_create was added in commit 9183df25fe7b194563db3fec6dc3202a5855839c
it allows anon mmap to have an fd, that can be shared, sealed and needs no
mount point, the uapi header for flags is linux/memfd.h
based on patch by Jens Gustedt.
mtx_t and cnd_t are defined in such a way that they are formally
"compatible types" with pthread_mutex_t and pthread_cond_t,
respectively, when accessed from a different translation unit. this
makes it possible to implement the C11 functions using the pthread
functions (which will dereference them with the pthread types) without
having to use the same types, which would necessitate either namespace
violations (exposing pthread type names in threads.h) or incompatible
changes to the C++ name mangling ABI for the pthread types.
for the rest of the types, things are much simpler; using identical
types is possible without any namespace considerations.
unfortunately this needs to be able to vary by arch, because of a huge
mess GCC made: the GCC definition, which became the ABI, depends on
quirks in GCC's definition of __alignof__, which does not match the
formal alignment of the type.
GCC's __alignof__ unexpectedly exposes the an implementation detail,
its "preferred alignment" for the type, rather than the formal/ABI
alignment of the type, which it only actually uses in structures. on
most archs the two values are the same, but on some (at least i386)
the preferred alignment is greater than the ABI alignment.
I considered using _Alignas(8) unconditionally, but on at least one
arch (or1k), the alignment of max_align_t with GCC's definition is
only 4 (even the "preferred alignment" for these types is only 4).
when manipulating the robust list, the order of stores matters,
because the code may be asynchronously interrupted by a fatal signal
and the kernel will then access the robust list in what is essentially
an async-signal context.
previously, aliasing considerations made it seem unlikely that a
compiler could reorder the stores, but proving that they could not be
reordered incorrectly would have been extremely difficult. instead
I've opted to make all the pointers used as part of the robust list,
including those in the robust list head and in the individual mutexes,
volatile.
in addition, the format of the robust list has been changed to point
back to the head at the end, rather than ending with a null pointer.
this is to match the documented kernel robust list ABI. the null
pointer, which was previously used, only worked because faults during
access terminate the robust list processing.
linux 3.14 introduced sched_getattr and sched_setattr syscalls in
commit d50dde5a10f305253cbc3855307f608f8a3c5f73
and the related SCHED_DEADLINE scheduling policy in
commit aab03e05e8f7e26f51dee792beddcb5cca9215a5
but struct sched_attr "extended scheduling parameters data structure"
is not yet exported to userspace (necessary for using the syscalls)
so related uapi definitions are not added yet.
The mips arch is special in that it uses different RLIMIT_
numbers than other archs, so allow bits/resource.h to override
the default RLIMIT_ numbers (empty on all archs except mips).
Reported by orc.
the definition was found to be incorrect at least for powerpc, and
fixing this cleanly requires making the definition arch-specific. this
will allow cleaning up the definition for other archs to make it more
specific, and reversing some of the ugliness (time_t hacks) introduced
with the x32 port.
this first commit simply copies the existing definition to each arch
without any changes. this is intentional, to make it easier to review
changes made on a per-arch basis.
Szabolcs Nagy
Rich Felker
rofl0r