Re: [PATCH 3/4] system/physmem.c: reorder usage and assertion of block

On Sat, 7 Feb 2026 at 10:24, Sergei Heifetz <[email protected]> wrote:
>
> On 2/4/26 17:53, Laurent Vivier wrote:
> > Le 04/02/2026 à 08:57, Sergei Heifetz a écrit :
> >> Reorder the code so the assertion of block occurs before it is
> >> used in the subsequent lines.
> >>
> >> Signed-off-by: Sergei Heifetz <[email protected]>
> >> ---
> >>   system/physmem.c | 4 ++--
> >>   1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/system/physmem.c b/system/physmem.c
> >> index b0311f4531..4308e02940 100644
> >> --- a/system/physmem.c
> >> +++ b/system/physmem.c
> >> @@ -2054,11 +2054,11 @@ static int memory_try_enable_merging(void
> >> *addr, size_t len)
> >>    */
> >>   int qemu_ram_resize(RAMBlock *block, ram_addr_t newsize, Error **errp)
> >>   {
> >> +    assert(block);
> >> +
> >>       const ram_addr_t oldsize = block->used_length;
> >>       const ram_addr_t unaligned_size = newsize;
> >>   -    assert(block);
> >> -
> >
> > According to coding style (docs/devel/style.rst):
> >
> > Mixed declarations (interleaving statements and declarations within
> > blocks) are generally not allowed.
> >
> >>       newsize = TARGET_PAGE_ALIGN(newsize);
> >>       newsize = REAL_HOST_PAGE_ALIGN(newsize);
> >
> > Thanks,
> > Laurent
>
> Should I remove the assertion altogether, then? I think the const
> qualifier on oldsize is more useful than the assertion.

I think personally I would drop the assertion. This falls into a
category I think of as "assertion doesn't buy us anything".
If block is NULL we're going to crash immediately when we
dereference it, so the assert doesn't help to turn a hard-to-debug
bug into an easy-to-debug bug (e.g. by catching incorrect values
long before they're used) or to turn a nasty kind of failure
into a safer one (e.g. by turning an array overrun into
an assertion).

And looking more closely, we call this function in only
two places:
 * migration/ram.c, where we've already dereferenced block
   in the code just before the call
 * system/memory.c, which asserts mr->ram_block before passing it in

So I think the assert in this function isn't buying us anything,
and the simplest thing is to delete it.

thanks
-- PMM