Hi Nick,
Le mer. 16 déc. 2020 à 18:08, Nick Desaulniers ndesaulniers@google.com a écrit :
On Wed, Dec 16, 2020 at 3:40 PM Paul Cercueil paul@crapouillou.net 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()?
Indeed.
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@vger.kernel.org # v4.7 Signed-off-by: Paul Cercueil paul@crapouillou.net
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);
Actually that would not work (I did try that), since the 4-byte size appended to the compressed payload is inside the *(.image) section. The code that appends it (in scripts/Makefile.lib, I think) doesn't seem to take care about aligning it to a 4-byte offset. I have no idea why it does with GCC and doesn't with Clang, and I have no idea why the compressed payload's size isn't aligned either.
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@google.com
Thanks.
Cheers, -Paul
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 littleendian */
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 expectit */ memcpy((void *)VMLINUX_LOAD_ADDRESS_ULL + image_size, -- 2.29.2
-- Thanks, ~Nick Desaulniers