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

["Richard W.M. Jones" <rjones@redhat.com>]

On Tue, Jan 30, 2024 at 01:04:46PM +0100, Kevin Wolf wrote:
> 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?

I guess not.  Stefan, any comments on whether we need to worry about
huge mem-region-alignment?  I'll post the updated patch as a new
message in a second.

Rich.

> 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
> > 

-- 
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