reuses a bit from CSIGNAL so it can only be used with unshare
and clone3, added in
linux commit 769071ac9f20b6a447410c7eaa55d1a5233ef40c
ns: Introduce Time Namespace
the time_t members in struct sched_param are just reserved space to
preserve size and alignment. when time_t changes to 64-bit on 32-bit
archs, this structure should not change.
make definition conditional on _REDIR_TIME64 to match the size of the
old time_t, which can be assumed to be long if _REDIR_TIME64 is
defined.
a _REDIR_TIME64 macro is introduced, which the arch's alltypes.h is
expected to define, to control redirection of symbol names for
interfaces that involve time_t and derived types. this ensures that
object files will only be linked to libc interfaces matching the ABI
whose headers they were compiled against.
along with time32 compat shims, which will be introduced separately,
the redirection also makes it possible for a single libc (static or
shared) to be used with object files produced with either the old
(32-bit time_t) headers or the new ones after 64-bit time_t switchover
takes place. mixing of such object files (or shared libraries) in the
same program will also be possible, but must be done with care; ABI
between libc and a consumer of the libc interfaces is guaranteed to
match by the the symbol name redirection, but pairwise ABI between
consumers of libc that define interfaces between each other in terms
of time_t is not guaranteed to match.
this change adds a dependency on an additional "GNU C" feature to the
public headers for existing 32-bit archs, which is generally
undesirable; however, the feature is one which glibc has depended on
for a long time, and thus which any viable alternative compiler is
going to need to provide. 64-bit archs are not affected, nor will
future 32-bit archs be, regardless of whether they are "new" on the
kernel side (e.g. riscv32) or just newly-added (e.g. a new sparc or
xtensa port). the same applies to newly-added ABIs for existing
machine-level archs.
these members are associated with an unsupported option group. with
time_t changing size on 32-bit archs, all interfaces taking struct
sched_param arguments would need redirection and compat shims in order
to be able to continue offering these members, for no benefit. just
convert them to reserved space instead.
since cpu sets can be dynamically allocated and have variable size,
accessing their contents via ->__bits is not valid; performing pointer
arithmetic outside the range of the size of the declared __bits array
results in undefined beahavior. instead, only use cpu_set_t for
fixed-size cpu set objects (instantiated by the caller) and as an
abstract pointer type for dynamically allocated ones. perform all
accesses simply by casting the abstract pointer type cpuset_t * back
to unsigned long *.
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.
gcc -Wsign-compare warns about expanded macros that were defined in
standard headers (before gcc 4.8) which can make builds fail that
use -Werror. changed macros: WIFSIGNALED, __CPU_op_S
this first commit just includes the CPU_* and sched_* interfaces, not
the pthread_* interfaces, which may be added later. simple
sanity-check testing has been done for the basic interfaces, but most
of the macros have not yet been tested.
linux's sched_* syscalls actually implement the TPS (thread
scheduling) functionality, not the PS (process scheduling)
functionality which the sched_* functions are supposed to have.
omitting support for the PS option (and having the sched_* interfaces
fail with ENOSYS rather than omitting them, since some broken software
assumes they exist) seems to be the only conforming way to do this on
linux.
the old behavior of exposing nothing except plain ISO C can be
obtained by defining __STRICT_ANSI__ or using a compiler option (such
as -std=c99) that predefines it. the new default featureset is POSIX
with XSI plus _BSD_SOURCE. any explicit feature test macros will
inhibit the default.
installation docs have also been updated to reflect this change.
several things are changed. first, i have removed the old __uniclone
function signature and replaced it with the "standard" linux
__clone/clone signature. this was necessary to expose clone to
applications anyway, and it makes it easier to port __clone to new
archs, since it's now testable independently of pthread_create.
secondly, i have removed all references to the ugly ldt descriptor
structure (i386 only) from the c code and pthread structure. in places
where it is needed, it is now created on the stack just when it's
needed, in assembly code. thus, the i386 __clone function takes the
desired thread pointer as its argument, rather than an ldt descriptor
pointer, just like on all other sane archs. this should not affect
applications since there is really no way an application can use clone
with threads/tls in a way that doesn't horribly conflict with and
clobber the underlying implementation's use. applications are expected
to use clone only for creating actual processes, possibly with new
namespace features and whatnot.
Szabolcs Nagy
Rich Felker
Nathan Zadoks