Re: [Valgrind-developers] issue with chaining and redirected functions (pthread_spin_lock)

[Julian S. <js...@ac...>]

On Friday, November 30, 2012, Petar Jovanovic wrote:
> It could happen there as well, but chaining made it worse as it removed
> a block with LL.

I'm not sure I understand what you mean.  Chaining just makes it cheaper
to get from one block to the next.  It does not change the order in which
the blocks are visited.

Anyway .. not directly relevant.


> If we introduce a change which would prevent redirections coming from
> branches and jumps (in contrast to branch-and-link and jump-and-link),
> would not that work for ARM as well?

It is true that "write PC+4 to the link register and set PC to
some new value" clearly indicates a call.  No problems there.

The difficulty is that "set PC to some new value but don't change the
link register" usually, but not always, indicates a non-call.  In
particular, if we are doing a tail call then there will simply be a jump
to the start of the new function (or this one, if recursive), which 
is no different from a conditional branch back to a loop that starts
at the beginning of this function.

So the presence/absence of writing the link register can't be used to
reliably distinguish the call/non-call cases.

J