Re: Memory leak in via_isa_realize()

[Peter Maydell]

On Mon, 21 Mar 2022 at 10:31, Thomas Huth <thuth@redhat.com> wrote:
> FYI, I'm seeing a memory leak in via_isa_realize() when building
> QEMU with sanitizers enabled or when running QEMU through valgrind:
> Same problem happens with qemu-system-ppc64 and the pegasos2 machine.
>
> No clue how to properly fix this... is it safe to free the pointer
> at the end of the function?

This is because the code is still using the old function
qemu_allocate_irqs(), which is almost always going to involve
it leaking memory. The fix is usually to rewrite the code to not use
that function at all, i.e. to manage its irq/gpio lines differently.
Probably the i8259 code should have a named GPIO output line
rather than wanting to be passed a qemu_irq in an init function,
and the via code should have an input GPIO line which it connects
up to the i8259. It looks from a quick glance like the i8259 and
its callers have perhaps not been completely QOMified.

In this specific case, though, it seems like the only thing that
the via_isa_request_i8259_irq() function does is pass the interrupt
signal through to its own s->cpu_intr, so I think a relatively
self-contained way to deal with the leak is to pass s->cpu_intr
into i8259_init() and drop the isa_irq allocated irq and its
associated helper function entirely. (There might be some subtlety
I'm missing that means that wouldn't work, of course.)

-- PMM