Re: [Qemu-devel] [PATCH] Error check find_ram_offset

[Markus Armbruster <armbru@redhat.com>]

Alex Williamson <alex.williamson@redhat.com> writes:

> Spotted via code review, we initialize offset to 0 to avoid a
> compiler warning, but in the unlikely case that offset is
> never set to something else, we should abort instead of return
> a value that will almost certainly cause problems.

Compiler warning pointed to the problem until commit 09d7ae90 "Fix
warning about uninitialized variable" papered over it.

> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>
>  exec.c |   11 +++++++++--
>  1 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 9dc4edb..70f6fb8 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2874,7 +2874,7 @@ static void *file_ram_alloc(RAMBlock *block,
>  static ram_addr_t find_ram_offset(ram_addr_t size)
>  {
>      RAMBlock *block, *next_block;
> -    ram_addr_t offset = 0, mingap = RAM_ADDR_MAX;
> +    ram_addr_t offset = RAM_ADDR_MAX, mingap = RAM_ADDR_MAX;
>  
>      if (QLIST_EMPTY(&ram_list.blocks))
>          return 0;
> @@ -2890,10 +2890,17 @@ static ram_addr_t find_ram_offset(ram_addr_t size)
>              }
>          }
>          if (next - end >= size && next - end < mingap) {
> -            offset =  end;
> +            offset = end;
>              mingap = next - end;
>          }
>      }
> +
> +    if (offset == RAM_ADDR_MAX) {
> +        fprintf(stderr, "Failed to find gap of requested size: %" PRIu64 "\n",
> +                (uint64_t)size);
> +        abort();
> +    }
> +
>      return offset;
>  }

The loop can't yield offset RAM_ADDR_MAX, because size needs to be zero
for next - end >= size to succeed, and that's not possible.

Reviewed-by: Markus Armbruster <armbru@redhat.com>