| Message ID | 56D6F958.2000109@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Mar 02, 2016 at 03:31:52PM +0100, Andreas Färber wrote: > Am 02.03.2016 um 14:52 schrieb Mark Rutland: > > On Wed, Mar 02, 2016 at 03:34:55AM +0100, Andreas Färber wrote: > >> Note: On the Vega S95 I need to change TEXT_OFFSET as follows, > >> in order to avoid the vendor U-Boot overwriting itself (fwiu); > >> for the Mini Mx that's reportedly not necessary. > >> > >> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > >> index 354d75402ace..b7cebdb8b1ce 100644 > >> --- a/arch/arm64/Makefile > >> +++ b/arch/arm64/Makefile > >> @@ -62,7 +62,7 @@ head-y := arch/arm64/kernel/head.o > >> ifeq ($(CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET), y) > >> TEXT_OFFSET := $(shell awk 'BEGIN {srand(); printf "0x%03x000\n", int(512 * rand())}') > >> else > >> -TEXT_OFFSET := 0x00080000 > >> +TEXT_OFFSET := 0x01080000 > >> endif > >> > >> # KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - 3)) - (1 << 61) > > > > Absolute NAK to this. TEXT_OFFSET is not open for platform-specific > > modification. > > Please read again. There is nothing to NAK here, it's a workaround for > testing my patches on my device! Even my own git queue has it clearly > labeled as "HACK:". Sure; I appreciate you need a workaround for the broken bootloader currently on the device. I'm simply heading off any attempts to upstream such changes. > Nothing you say here indicates that this is breaking any particular > kernel feature or damaging the device, so unless you propose a different > way to solve the problem I see no way around it for now. As far as I am aware, this should not result in damage to your device. However, it runs directly counter to single-image, and other parts of the kernel _may_ rely on the existing limits on TEXT_OFFSET. So it's not suitable for upstream, and you _may_ encounter issues as a result. > > Why can you not just load the Image 2MB higher regardless? Does the > > U-Boot on this platform actually read TEXT_OFFSET and take it into > > account? > > Yes, U-Boot checks the ELF(?) header and tries to copy the image to the > indicated offset if it isn't loaded there already. The vendor's kernel > has the adjusted offset and works; So the vendor deliberately changed the kernel Image in an unsupported fashion, resulting in a divergent boot protocol. This is incredibly unfortunate. > if I use unmodified mainline kernels then I get weird exceptions from > before entering the kernel, my assumption being that U-Boot code gets > overwritten. > > http://openlinux.amlogic.com:8000/download/ARM/u-boot/ > > This problem might go away if we had a proper upstream-based U-Boot; I'm > not familiar enough with U-Boot to fix that myself and would hate to > mess with U-Boot on eMMC, for lack of JTAG pins on this device. > The Odroid-C2 (which I do not have access to yet) has instructions how > to place U-Boot on an SD card, making it safer to experiment with. > http://odroid.com/dokuwiki/doku.php?id=en:c2_partition_table This is probably the right path to a solution. > >> This in turn runs into an apparent regression introduced with the > >> text offset randomization: > >> > >> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > >> index 6ebd204da16a..afdec27c8871 100644 > >> --- a/arch/arm64/kernel/head.S > >> +++ b/arch/arm64/kernel/head.S > >> @@ -48,7 +48,7 @@ > >> #elif (PAGE_OFFSET & 0x1fffff) != 0 > >> #error PAGE_OFFSET must be at least 2MB aligned > >> #elif TEXT_OFFSET > 0x1fffff > >> -#error TEXT_OFFSET must be less than 2MB > >> +//#error TEXT_OFFSET must be less than 2MB > >> #endif > >> > >> #define KERNEL_START _text > > > > This is not a regression. As above, TEXT_OFFSET is not supposed to be > > modified in a platform-specific manner. > > It is in fact an unexplained behavioral change in > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=da57a369d3bc5cd61db90f7e9555840381db9b09 Yes, strictly speaking it is a change. No, it is not a regression, since TEXT_OFFSET was _never_ open to such platform-specific modification. Thanks, Mark.
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 3ba0fc0..69dafe9 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -37,8 +37,12 @@ #define KERNEL_RAM_VADDR (PAGE_OFFSET + TEXT_OFFSET) -#if (KERNEL_RAM_VADDR & 0xfffff) != 0x80000 -#error KERNEL_RAM_VADDR must start at 0xXXX80000 +#if (TEXT_OFFSET & 0xf) != 0 +#error TEXT_OFFSET must be at least 16B aligned +#elif (PAGE_OFFSET & 0xfffff) != 0 +#error PAGE_OFFSET must be at least 2MB aligned +#elif TEXT_OFFSET > 0xfffff +#error TEXT_OFFSET must be less than 2MB #endif .macro pgtbl, ttb0, ttb1, virt_to_phys