On Wed, Mar 20, 2019 at 7:26 PM Todd Kjos <tkjos@xxxxxxxxxx> wrote:
> I can send you a patch tomorrow (I won't be able to test it though).
I may not know much about binder, but I do know how to run the test suite :)
Thanks Todd.
> On Wed, Mar 20, 2019 at 4:23 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
> >
> > On Wed, Mar 20, 2019 at 3:50 PM Todd Kjos <tkjos@xxxxxxxxxx> wrote:
> > >
> > > Paul,
> > >
> > > Looking at main() in test_binder.c...
> > >
> > > int main(int argc, char **argv)
> > > {
> > >
> > > [...]
> > >
> > > // Line 493
> > > struct binder_write_read bwr;
> > > struct flat_binder_object obj;
> > > struct {
> > > uint32_t cmd;
> > > struct binder_transaction_data txn;
> > > } __attribute__((packed)) writebuf;
> > > unsigned int readbuf[32];
> > >
> > > [...]
> > > // Line 630
> > > writebuf.txn.data.ptr.buffer = (uintptr_t)&obj;
> > > writebuf.txn.data.ptr.offsets = (uintptr_t)&obj + // [A]
> > > sizeof(struct
> > > flat_binder_object);
> > >
> > > bwr.write_buffer = (uintptr_t)&writebuf;
> > > bwr.write_size = sizeof(writebuf);
> > >
> > > It looks like bwr.txn.data.ptr.offsets points off the end of obj (see
> > > [A] above), which means the binder driver will read compiler-dependent
> > > stack data as the offset for the object. If it happens to be 0, then
> > > the test will work (read the object from offset 0). If it's not 0,
> > > then most likely offset > data_size (which is what found that BUG_ON
> > > case). With my patch applied, this will just cause an error to be
> > > returned (what you are seeing now).
> > >
> > > Same thing when you test with v5.0 -- if the offset happens to be 0,
> > > then the test will succeed. If not, then the test will fail because
> > > the transaction fails in an unexpected way.
> >
> > That might explain why the test used to work, but now fails - a
> > different compiler (I rebuild the test before each test run).
> >
> > Keeping in mind I'm really quite ignorant when it comes to binder, how
> > would you suggest fixing the test?
> >
> > --
> > paul moore
> > www.paul-moore.com
--
paul moore
www.paul-moore.com
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