Re: [PATCH 2/5] support: don't pass to resolv_test_start a big struct by value

[Konstantin Kharlamov <hi-angel at yandex dot ru>]

On Пн, Mar 25, 2019 at 11:33:28, Florian Weimer <fw@deneb.enyo.de> 
wrote:
> * Konstantin Kharlamov:
>
> >  diff --git a/support/resolv_test.h b/support/resolv_test.h
> >  index c9e48205ab..880330ad5c 100644
> >  --- a/support/resolv_test.h
> >  +++ b/support/resolv_test.h
> >  @@ -116,7 +116,7 @@ void resolv_test_init (void);
> >      needed.  As a side effect, NSS is reconfigured to use nss_dns 
> > only
> >      for aplicable databases, and the process may enter a network
> >      namespace for better isolation.  */
> >  -struct resolv_test *resolv_test_start (struct 
> > resolv_redirect_config);
> >  +struct resolv_test *resolv_test_start (const struct 
> > resolv_redirect_config*);
>
> This patch would adjusting all the tests that call resolv_test_start,
> and these changes are missing from the patch.  It is unclear how this
> change would be an improvement because most tests call
> resolv_test_start exactly once and the parameter object is never used
> again.  Passing a pointer requires writing the argument object to the
> stack *and* supplying its address to resolv_test_start, which requires
> more work.  (Maybe some targets have more optimized code for struct
> initialization than passing many zero arguments, but that's a GCC
> issue which will eventually be fixed.)

Wow, are you saying that in the assembly the address that gets passed 
to resolve_test_start() would be not the address of struct, but instead 
an address of an addres on a stack that is an address of the struct…? 
That doesn't sound right, is that some calling convention? I've never 
heard of this.