On Tue, 1 Oct 2019, Ed Maste wrote:
On Tue, 1 Oct 2019 at 12:23, Brooks Davis <[email protected]> wrote:
This isn't true with CHERI and as a result I've moved the variadic
argument handling (except for syscall() and __syscall()) into libc.
My grep found: open, openat, fcntl, semsys, msgsys, shmsys
Is that the full list?
I already wrote that this is quite broken for open and fcntl in POSIX.
hecking some details shows that it is more fundamentally broken than I
thought:
- for open(), the type of the mode argument passed by the caller is
unspecified. Whatever it is, it is "taken" as type mode_t, whatevr
"taking" is. Since historical mode_t has only 16 bits, it can be
represented by int even on systems with 16-bit ints, so the caller
can start with either mode_t or int provided mode_t is no larger than
historical mode_t and ints are either larger than 16 bits or 16 bits
and not too exotic (the sign bit might cause problems if not 2's
complement)
- for fcntl() with F_SETOWN, the type of the pid argument passed by the
caller is unspecified. Whatever it is, it is "taken" as type int.
Thus if pid_t is larger than int, passing all possible values of
pid_t is impossible. If also PID_MAX <= INT_MAX and all values of
pid_t are actually <= PID_MAX, then all possible (positive) values
can be passed, but the iplementation may have to do extra work to
properly break a passed __default_promotion_of(pid_t) type by "taking"
it as an int.
This was discussed on the POSIX list recently. IMO it is too late and
not useful to change the old specification to "take" the arg as anything
except int. So pid_t might as well be specified as being a signed integer
type whose default promotion is int. It is currently specified as being
a signed integer type (with any size or exoticness).
Bruce
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