[Valgrind-developers] New things to play with

[Jeremy F. <je...@go...>]

I've been pretty busy over the last few weeks, and I've finally got
something to show for it.

The large change is the rewrite of Valgrind's syscall and signal
handling.  This change now makes Valgrind cope consistently with
blocking syscalls without having to intercept them and turn them into
non-blocking syscalls.  

This also required that I rewrite the signal handling, which is now much
more Posix compliant.  Threads have their own signal masks, the right
signals are masked while handlers are running, kill(getpid(), sig) is no
synchronous, and a large number of minor changes which make things a lot
happier.  Also, SA_SIGINFO is fully implemented, as are all the other
sigaction flags except for SA_RESTORER.  There are even sensible default
handlers for fatal signals (ie, if your program takes a SIGSEGV and
there's no handler for it, Valgrind will catch it and print useful
messages about what happened).

In addition to the normal "run commands and see how they work", I've
been using the posix test suite (http://posixtest.sf.net) to explore all
the fine corners.  There's still a lot of stuff which isn't compliant,
mostly because Valgrind doesn't implement everything (pthread_barrier_*
anyone?) rather than because it doesn't work.

That said, this is all rather fresh new code, so I'd like people to test
it out before we consider moving it into the mainline.  The big caveat
is that I've only tested it seriously with Linux 2.6 kernels, and
somewhat with standard 2.4.  I gather RedHat's 2.4 is somewhat different
from standard 2.4 in ways which matter to Valgrind.

This patch still doesn't implement clone() for application use, but it
should be relatively simple to add.  The main problems are 1) choosing
which subset to impement, 2) getting all the clone semantics correct,
and 3) choosing which version of clone to implement (it changed a lot
between 2.4 and 2.6).

If you're using 2.5/2.6 kernel versions, I recommend getting the
absolute latest (2.6.0-test3 at the moment), because there have been a
number of bugs fixed in the thread/signal area lately.

All this is available at http://www.goop.org/~jeremy/valgrind/snapshots/

BTW, if anyone is interested, I've been using Bitkeeper for my Valgrind
development.  All my changes are available at
bk://valgrind.bkbits.net/{valgrind,syscalls,fully-patched}; see
http://valgrind.bkbits.net for the web interface.

	J