Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Kevin Wolf <kwolf@redhat.com>]

Am 30.01.2024 um 11:30 hat Richard W.M. Jones geschrieben:
> On Tue, Jan 30, 2024 at 09:51:59AM +0100, Kevin Wolf wrote:
> > Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> > > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > > version of GCC):
> > > 
> > > ../block/blkio.c: In function ‘blkio_file_open’:
> > > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> > >   857 |                            &s->mem_region_alignment);
> > >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> > >       |                            |
> > >       |                            size_t * {aka unsigned int *}
> > > In file included from ../block/blkio.c:12:
> > > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> > >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> > >       |                                                         ~~~~~~~~~~^~~~~
> > > 
> > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > 
> > Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
> > instead of keeping it size_t and doing an additional conversion with
> > a check that requires an #if (probably to avoid a warning on 64 bit
> > hosts because the condition is never true)?
> 
> The smaller change (attached) does work on i686, but this worries me a
> little (although it doesn't give any error or warning):
> 
>     if (((uintptr_t)host | size) % s->mem_region_alignment) {
>     error_setg(errp, "unaligned buf %p with size %zu", host, size);
>         return BMRR_FAIL;
>     }

I don't see the problem? The calculation will now be done in 64 bits
even on a 32 bit host, but that seems fine to me. Is there a trap I'm
missing?

Kevin

> From 500f3a81652dcefa79a4864c1f3fa6747c16952e Mon Sep 17 00:00:00 2001
> From: "Richard W.M. Jones" <rjones@redhat.com>
> Date: Mon, 29 Jan 2024 18:20:46 +0000
> Subject: [PATCH] block/blkio: Make s->mem_region_alignment be 64 bits
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> With GCC 14 the code failed to compile on i686 (and was wrong for any
> version of GCC):
> 
> ../block/blkio.c: In function ‘blkio_file_open’:
> ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
>   857 |                            &s->mem_region_alignment);
>       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
>       |                            |
>       |                            size_t * {aka unsigned int *}
> In file included from ../block/blkio.c:12:
> /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
>    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
>       |                                                         ~~~~~~~~~~^~~~~
> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  block/blkio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blkio.c b/block/blkio.c
> index 0a0a6c0f5fd..bc2f21784c7 100644
> --- a/block/blkio.c
> +++ b/block/blkio.c
> @@ -68,7 +68,7 @@ typedef struct {
>      CoQueue bounce_available;
>  
>      /* The value of the "mem-region-alignment" property */
> -    size_t mem_region_alignment;
> +    uint64_t mem_region_alignment;
>  
>      /* Can we skip adding/deleting blkio_mem_regions? */
>      bool needs_mem_regions;
> -- 
> 2.43.0
>