On Sat, Oct 7, 2023 at 10:05 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
>
> The current TO_NATIVE() has some limitations:
>
> 1) You cannot cast the argument.
>
> 2) You cannot pass a variable marked as 'const'.
>
> 3) Passing an array is a bug, but it is not detected.
>
> Impelement TO_NATIVE() using bswap_*() functions. These are GNU
> extensions. If we face portability issues, we can port the code from
> include/uapi/linux/swab.h.
>
> With this change, get_rel_type_and_sym() can be simplified by casting
> the arguments directly.
>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
>
> scripts/mod/modpost.c | 13 ++++---------
> scripts/mod/modpost.h | 25 ++++++++++++-------------
> 2 files changed, 16 insertions(+), 22 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 2f3b0fe6f68d..99476a9695c5 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1410,15 +1410,10 @@ static void get_rel_type_and_sym(struct elf_info *elf, uint64_t r_info,
> return;
> }
>
> - if (is_64bit) {
> - Elf64_Xword r_info64 = r_info;
> -
> - r_info = TO_NATIVE(r_info64);
> - } else {
> - Elf32_Word r_info32 = r_info;
> -
> - r_info = TO_NATIVE(r_info32);
> - }
> + if (is_64bit)
> + r_info = TO_NATIVE((Elf64_Xword)r_info);
> + else
> + r_info = TO_NATIVE((Elf32_Word)r_info);
>
> *r_type = ELF_R_TYPE(r_info);
> *r_sym = ELF_R_SYM(r_info);
> diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
> index 6413f26fcb6b..1392afec118c 100644
> --- a/scripts/mod/modpost.h
> +++ b/scripts/mod/modpost.h
> @@ -1,4 +1,5 @@
> /* SPDX-License-Identifier: GPL-2.0 */
> +#include <byteswap.h>
> #include <stdbool.h>
> #include <stdio.h>
> #include <stdlib.h>
> @@ -51,21 +52,19 @@
> #define ELF_R_TYPE ELF64_R_TYPE
> #endif
>
> +#define bswap(x) \
> +({ \
> + _Static_assert(sizeof(x) == 1 || sizeof(x) == 2 || \
Seems fine, but do we need to support folks trying to swap 1B values?
i.e. is someone calling TO_NATIVE with 1B values? Seems silly unless
one of these types is variable length dependent on the target machine
type?
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> + sizeof(x) == 4 || sizeof(x) == 8, "bug"); \
> + (typeof(x))(sizeof(x) == 2 ? bswap_16(x) : \
> + sizeof(x) == 4 ? bswap_32(x) : \
> + sizeof(x) == 8 ? bswap_64(x) : \
> + x); \
> +})
> +
> #if KERNEL_ELFDATA != HOST_ELFDATA
>
> -static inline void __endian(const void *src, void *dest, unsigned int size)
> -{
> - unsigned int i;
> - for (i = 0; i < size; i++)
> - ((unsigned char*)dest)[i] = ((unsigned char*)src)[size - i-1];
> -}
> -
> -#define TO_NATIVE(x) \
> -({ \
> - typeof(x) __x; \
> - __endian(&(x), &(__x), sizeof(__x)); \
> - __x; \
> -})
> +#define TO_NATIVE(x) (bswap(x))
>
> #else /* endianness matches */
>
> --
> 2.39.2
>
--
Thanks,
~Nick Desaulniers
