On Wed, Dec 16, 2020 at 3:40 PM Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
>
> The compressed payload is not necesarily 4-byte aligned, at least when
> compiling with Clang. In that case, the 4-byte value appended to the
> compressed payload that corresponds to the uncompressed kernel image
> size must be read using get_unaligned_le().
Should it be get_unaligned_le32()?
>
> This fixes Clang-built kernels not booting on MIPS (tested on a Ingenic
> JZ4770 board).
>
> Fixes: b8f54f2cde78 ("MIPS: ZBOOT: copy appended dtb to the end of the kernel")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.7
> Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Hi Paul, thanks for the patch (and for testing with Clang)!
Alternatively, we could re-align __image_end to the next 4B multiple
via:
diff --git a/arch/mips/boot/compressed/ld.script
b/arch/mips/boot/compressed/ld.script
index 0ebb667274d6..349919eff5fb 100644
--- a/arch/mips/boot/compressed/ld.script
+++ b/arch/mips/boot/compressed/ld.script
@@ -27,6 +27,7 @@ SECTIONS
/* Put the compressed image here */
__image_begin = .;
*(.image)
+ . = ALIGN(4);
__image_end = .;
CONSTRUCTORS
. = ALIGN(16);
The tradeoff being up to 3 wasted bytes of padding in the compressed
image, vs fetching one value slower (assuming unaligned loads are
slower than aligned loads MIPS, IDK). I doubt decompress_kernel is
called repeatedly, so let's take the byte saving approach of yours by
using unaligned loads!
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> ---
> arch/mips/boot/compressed/decompress.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/boot/compressed/decompress.c b/arch/mips/boot/compressed/decompress.c
> index c61c641674e6..47c07990432b 100644
> --- a/arch/mips/boot/compressed/decompress.c
> +++ b/arch/mips/boot/compressed/decompress.c
> @@ -117,7 +117,7 @@ void decompress_kernel(unsigned long boot_heap_start)
> dtb_size = fdt_totalsize((void *)&__appended_dtb);
>
> /* last four bytes is always image size in little endian */
> - image_size = le32_to_cpup((void *)&__image_end - 4);
> + image_size = get_unaligned_le32((void *)&__image_end - 4);
>
> /* copy dtb to where the booted kernel will expect it */
> memcpy((void *)VMLINUX_LOAD_ADDRESS_ULL + image_size,
> --
> 2.29.2
>
--
Thanks,
~Nick Desaulniers
