[oi-dev] valgrind and epoll(5) illumos issue

[stes@PANDORA.BE]

The original Squeak (Smalltalk-80) runtime (similar to squeak-4) uses signal driven,
non-blocking I/O using select(3c).

An interesting ongoing recent project in the world of Squeak,
is to add epoll(7) support to squeak-5;
so basically a developer added epoll(5) for event-driven I/O.

https://illumos.org/man/5/epoll

This is not really OpenIndiana specific but since I use squeak on OpenIndiana, I'm asking here.

The configure script detects that OI supports epoll (via /usr/include/sys/epoll.h),
and it enables the support which compiles fine, and it basically seems to work fine, I think.

However when I run the executable using the valgrind tool 

# pkg info -r valgrind
          Name: developer/debug/valgrind
       Summary: Valgrind: instrumentation framework and tools to detect memory
                and threading problems

Then I run into the following issue.

In illumos-gate/usr/src/uts/common/sys/devpoll.h the following is defined

$ grep DPIOC uts/common/sys/devpoll.h
#define		DPIOC	(0xD0 << 8)
#define	DP_POLL		(DPIOC | 1)	/* poll on fds cached via /dev/poll */
#define	DP_ISPOLLED	(DPIOC | 2)	/* is this fd cached in /dev/poll */
#define	DP_PPOLL	(DPIOC | 3)	/* ppoll on fds cached via /dev/poll */
#define	DP_EPOLLCOMPAT	(DPIOC | 4)	/* turn on epoll compatibility */

Now valgrind reports the following :

==8531== Warning: noted but unhandled ioctl 0xd004 with no size/direction hints.
==8531==    This could cause spurious value errors to appear.
==8531==    See README_MISSING_SYSCALL_OR_IOCTL for guidance on writing a proper
 wrapper.
==8531== Syscall param write(buf) points to uninitialised byte(s)
==8531==    at 0xFFFD5D8AA: __write (in /lib/amd64/libc.so.1)
==8531==    by 0xFFFD30670: epoll_ctl (in /lib/amd64/libc.so.1)

Note that the unhandled ioctl is 0xd004 which is the DP_EPOLLCOMPAT I suspect.

So OpenIndiana valgrind has no 'wrapper' for DP_EPOLLCOMPAT.

Also valgrind complains about the uninitialized bytes in epoll_ctl,
which perhaps are due to :

illumos-gate/usr/src/lib/libc/port/sys/epoll.c

int
epoll_ctl(int epfd, int op, int fd, struct epoll_event *event)
{
        dvpoll_epollfd_t epoll[2];

        res = write(epfd, epoll, sizeof (epoll[0]) * (i + 1));


I am not sure but valgrind may be complaining about passing epoll argument to write().

Perhaps this could be patched at the OpenIndiana level,
but ideally the Illumos contributors could contact valgrind.org to patch valgrind,
and/or the illumos sources (if required).

Also that would fix the issue for all Illumos based distributions, not just for OpenIndiana,
provided OpenIndiana would then incorporate/update its valgrind package.

I'm asking it here on OI-dev because OI is what I happen to use when observing this,
but has anyone perhaps seen this/or already fixed it perhaps ?

Thanks,
David Stes