On Thu, Sep 01, 2016 at 06:58:29PM +0800, zijun_hu wrote:
> From: zijun_hu <zijun_hu@xxxxxxx>
>
> regard FDT_SW_MAGIC as good fdt magic during mapping fdt area
> see fdt_check_header() for details
It looks like we should only see FDT_SW_MAGIC for a FDT that was in the
process of being created, but was not finished. So I'm somewhat confused
as to why fdt_check_header() would allow this.
Neither ePAPR nor the new devicetree spec define FDT_SW_MAGIC. They both
only define 0xd00dfeed as a valid magic value. In libfdt, FDT_SW_MAGIC
is an internal constant, and it looks like fdt_check_header() simply
accepts this for convenience within libfdt.
Given all of that, it looks like the kernel should *not* accept
FDT_SW_MAGIC in any case.
Why do you think this is necessary? Have you seen a problem in practice?
> --- a/scripts/dtc/libfdt/fdt.h
> +++ b/scripts/dtc/libfdt/fdt.h
> @@ -92,7 +92,8 @@ struct fdt_property {
>
> #endif /* !__ASSEMBLY */
>
> -#define FDT_MAGIC 0xd00dfeed /* 4: version, 4: total size */
> +/* 4: version, 4: total size */
> +#define FDT_MAGIC ((fdt32_t)0xd00dfeed)
> #define FDT_TAGSIZE sizeof(fdt32_t)
>
> #define FDT_BEGIN_NODE 0x1 /* Start node: full name */
> diff --git a/scripts/dtc/libfdt/libfdt.h b/scripts/dtc/libfdt/libfdt.h
> index 59ca33976e56..6998f9249183 100644
> --- a/scripts/dtc/libfdt/libfdt.h
> +++ b/scripts/dtc/libfdt/libfdt.h
> @@ -54,6 +54,8 @@
> #include "libfdt_env.h"
> #include "fdt.h"
>
> +#define FDT_SW_MAGIC (~FDT_MAGIC)
> +
> #define FDT_FIRST_SUPPORTED_VERSION 0x10
> #define FDT_LAST_SUPPORTED_VERSION 0x11
>
> diff --git a/scripts/dtc/libfdt/libfdt_internal.h b/scripts/dtc/libfdt/libfdt_internal.h
> index 02cfa6fb612d..f4efde0119f2 100644
> --- a/scripts/dtc/libfdt/libfdt_internal.h
> +++ b/scripts/dtc/libfdt/libfdt_internal.h
> @@ -90,6 +90,4 @@ static inline struct fdt_reserve_entry *_fdt_mem_rsv_w(void *fdt, int n)
> return (void *)(uintptr_t)_fdt_mem_rsv(fdt, n);
> }
>
> -#define FDT_SW_MAGIC (~FDT_MAGIC)
> -
> #endif /* _LIBFDT_INTERNAL_H */
Regardless of the above, changes to libfdt must happen in the upstream
libfdt codebase first.
Thanks,
Mark.
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