Hi Nick,
Le mer. 16 déc. 2020 à 18:08, Nick Desaulniers
<ndesaulniers@xxxxxxxxxx> a écrit :
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()?
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@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);
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@xxxxxxxxxx>
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 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
