On Fri, Jun 18, 2021 at 06:20:27PM +0100, Andre Przywara wrote:
> With -Wsign-compare, compilers warn about a mismatching signedness in
> the different legs of the conditional operator, in fdtget.c.
>
> In the questionable expression, we are constructing a 16-bit value out of
> two unsigned 8-bit values, however are relying on the compiler's
> automatic expansion of the uint8_t to a larger type, to survive the left
> shift. This larger type happens to be an "int", so this part of the
> expression becomes signed.
>
> Fix this by explicitly blowing up the uint8_t to a larger *unsigned* type,
> before doing the left shift. And while we are at it, convert the hardly
> readable conditional operator usage into a sane switch/case expression.
>
> This fixes "make fdtget", when compiled with -Wsign-compare.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
Applied, thanks.
> ---
> fdtget.c | 10 ++++++++--
> libfdt/libfdt.h | 7 +++++++
> 2 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/fdtget.c b/fdtget.c
> index 777582e..54fc6a0 100644
> --- a/fdtget.c
> +++ b/fdtget.c
> @@ -62,8 +62,14 @@ static int show_cell_list(struct display_info *disp, const char *data, int len,
> for (i = 0; i < len; i += size, p += size) {
> if (i)
> printf(" ");
> - value = size == 4 ? fdt32_ld((const fdt32_t *)p) :
> - size == 2 ? (*p << 8) | p[1] : *p;
> + switch (size) {
> + case 4: value = fdt32_ld((const fdt32_t *)p); break;
> + case 2: value = fdt16_ld((const fdt16_t *)p); break;
> + case 1:
> + default:
> + value = *p;
> + break;
> + }
> printf(fmt, value);
> }
>
> diff --git a/libfdt/libfdt.h b/libfdt/libfdt.h
> index 73467f7..7f117e8 100644
> --- a/libfdt/libfdt.h
> +++ b/libfdt/libfdt.h
> @@ -131,6 +131,13 @@ uint32_t fdt_next_tag(const void *fdt, int offset, int *nextoffset);
> * to work even with unaligned pointers on platforms (such as ARMv5) that don't
> * like unaligned loads and stores.
> */
> +static inline uint16_t fdt16_ld(const fdt16_t *p)
> +{
> + const uint8_t *bp = (const uint8_t *)p;
> +
> + return ((uint16_t)bp[0] << 8) | bp[1];
> +}
> +
> static inline uint32_t fdt32_ld(const fdt32_t *p)
> {
> const uint8_t *bp = (const uint8_t *)p;
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
Attachment:
signature.asc
Description: PGP signature
