On Mon, Oct 12, 2020 at 05:19:40PM +0100, Andre Przywara wrote:
65;6003;1c> With -Wsign-compare, compilers warn about a mismatching signedness in
> comparisons in fdtdump.c.
>
> The "len" parameter to valid_header() refers to a memory size, not a
> file offset, so the (unsigned) size_t is better fit, and fixes the
> warning nicely.
>
> In the main function we compare the difference between two pointers,
> which produces a signed ptrdiff_t type. However the while loop above the
> comparison makes sure that "p" always points before "endp" (by virtue of
> the limit in the memchr() call). This means "endp - p" is never
> negative, so we can safely cast this expression to an unsigned type.
>
> This fixes "make fdtdump", when compiled with -Wsign-compare.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
> fdtdump.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fdtdump.c b/fdtdump.c
> index 9613bef..ec67f99 100644
> --- a/fdtdump.c
> +++ b/fdtdump.c
> @@ -18,7 +18,7 @@
> #include "util.h"
>
> #define FDT_MAGIC_SIZE 4
> -#define MAX_VERSION 17
> +#define MAX_VERSION 17U
>
> #define ALIGN(x, a) (((x) + ((a) - 1)) & ~((a) - 1))
> #define PALIGN(p, a) ((void *)(ALIGN((unsigned long)(p), (a))))
> @@ -163,7 +163,7 @@ static const char * const usage_opts_help[] = {
> USAGE_COMMON_OPTS_HELP
> };
>
> -static bool valid_header(char *p, off_t len)
> +static bool valid_header(char *p, size_t len)
> {
> if (len < sizeof(struct fdt_header) ||
> fdt_magic(p) != FDT_MAGIC ||
> @@ -235,7 +235,7 @@ int main(int argc, char *argv[])
> }
> ++p;
> }
> - if (!p || endp - p < sizeof(struct fdt_header))
> + if (!p || (unsigned)(endp - p) < sizeof(struct fdt_header))
I think (size_t) would be more appropriate here, since it will match
the other size of the comparison, though it's very unlikely to cause a
problem in practice.
> die("%s: could not locate fdt magic\n", file);
> printf("%s: found fdt at offset %#tx\n", file, p - buf);
> buf = 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
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