Re: [PATCH] libxl: virtio: Fix build error for 32-bit platforms

[Anthony PERARD <anthony.perard@citrix.com>]

On Thu, Dec 15, 2022 at 07:01:40PM +0530, Viresh Kumar wrote:
> The field 'base' in 'struct libxl_device_virtio' is defined as uint64,
> while we are printing it with '%lu', which is 32bit only 32-bit
> platforms. And so generates a error like:
> 
>   libxl_internal.h:4388:51: error: format '%lu' expects argument of type 'long
>   unsigned int', but argument 3 has type 'uint64_t' {aka 'long long unsigned
>   int'} [-Werror=format=]
> 
> Fix the same by using PRIx64 instead.
> 
> Now that the base name is available in hexadecimal format, prefix it
> with '0x' as well, which strtoul() also depends upon since base passed
> is 0.
> 
> Fixes: 43ba5202e2ee ("libxl: add support for generic virtio device")
> Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> Couldn't test on 32-bit platforms yet, but works fine for 64 bit one.
> 
>  tools/libs/light/libxl_virtio.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libs/light/libxl_virtio.c b/tools/libs/light/libxl_virtio.c
> index 6a38def2faf5..2217bda8a253 100644
> --- a/tools/libs/light/libxl_virtio.c
> +++ b/tools/libs/light/libxl_virtio.c
> @@ -45,12 +45,12 @@ static int libxl__set_xenstore_virtio(libxl__gc *gc, uint32_t domid,
>      const char *transport = libxl_virtio_transport_to_string(virtio->transport);
>  
>      flexarray_append_pair(back, "irq", GCSPRINTF("%u", virtio->irq));
> -    flexarray_append_pair(back, "base", GCSPRINTF("%lu", virtio->base));
> +    flexarray_append_pair(back, "base", GCSPRINTF("0x%"PRIx64, virtio->base));

There is also PRIu64 that exist, which would be perfect to replace %u.
Could we use that instead?

I'd rather not have to think about which base is used for numbers in
xenstore. I can't find any hexadecimal numbers in xenstore for a simple
guest at the moment, so probably best to avoid adding one. And using
hexadecimal isn't needed to fix the build.

Thanks,

-- 
Anthony PERARD