On 09/05/2018 11:05 AM, Paul Eggert wrote:
Eric Blake wrote:
While this indeed accesses a parameter not passed by the caller, it is
a harmless access.
#if HAVE_FCNTL
+ /* Pass a pointer as a trailing argument. Although this is
+ not strictly kosher in theory, in practice it's good enough. */
void *p = va_arg (arg, void *);
result = fcntl (fd, action, p);
And for the record, our testsuite tests that this comment actually holds
on all platforms that we care about (that is, a caller passing int,
rpl_fcntl() parsing it as void* and passing it on as void*, then the
kernel reusing it as int, does not suffer from data corruption, even on
platforms where pointers are 64 bits and rpl_fcntl() therefore
read/passed on 32 bits of garbage alongside the real int):
https://git.savannah.gnu.org/cgit/gnulib.git/tree/tests/test-fcntl.c#n102
The test does not cover the case of rpl_fcntl() passing on garbage to a
function that will not consume the argument, but we could add that if it
is desired.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
