On 7.10.2024 10:23 PM, Linus Walleij wrote: > On Mon, Oct 7, 2024 at 6:35 PM Karl Chan <exxxxkc@xxxxxxxxxxxxxxx> wrote: > >> Also The original firmware from Linksys can only boot ARM32 kernels. >> >> As of now There seems to be no way to boot ARM64 kernels on those device. > > So this is a Cortex-A53 Aarch64 system running in ARM32 mode. > > So I got this interactive U-boot log from Karl showing how the attempt > to boot an Aarch64 kernel manifests: > > CBT U-Boot ver: 3.2.08 ([IPQ5018].[SPF11.3].[CSU2]) > > ## Loading kernel from FIT Image at 44000000 ... > Using 'standard' configuration > Trying 'kernel' kernel subimage > Description: Kernel > Type: Kernel Image > Compression: uncompressed > Data Start: 0x440000a8 > Data Size: 8249289 Bytes = 7.9 MiB > Architecture: AArch64 > OS: Linux > Load Address: 0x41208000 > Entry Point: 0x41208000 > Verifying Hash Integrity ... OK > (...) > ## Loading ramdisk from FIT Image at 44000000 ... > (...) > ## Loading fdt from FIT Image at 44000000 ... > (...) > fdt_fixup_qpic: QPIC: unable to find node '/soc/qpic-nand@79b0000' > Could not find PCI in device tree > Using machid 0x8040001 from environment > > Starting kernel ... > > undefined instruction > pc : [<41208004>] lr : [<4a921f8f>] > reloc pc : [<41208004>] lr : [<4a921f8f>] > sp : 4a822838 ip : 00000001 fp : 00000000 > r10: 4a83b914 r9 : 4a822ea0 r8 : 00000000 > r7 : 00000000 r6 : 41208000 r5 : 4a97d848 r4 : 00000000 > r3 : 644d5241 r2 : 4a0ae000 r1 : 08040001 r0 : 00000000 > Flags: nzCV IRQs off FIQs off Mode SVC_32 > Resetting CPU ... > > resetting ... > > So perhaps someone knows how we can get around this. > > It seems to me the U-Boot is in 32bit mode and tries to just > execute an Aarch64 binary and that doesn't work. > > What we need is a 32bit mode preamble that can switch > the machine to Aarch64 and continue. > > I don't know *how* to do that, but I would *guess* a botched > return from exception where you provide your own stack > with the Aarch64 state hardcoded on it should do the job? > > The Aarch64 maintainers will know what to do. > > Surely it should be possible to add a little code snippet > to do this somewhere in memory, and that in turn jumps > to execute the actual Aarch64 kernel in Aarch64 mode? Not sure about this one, but older (10+yo) qcom socs had a secure call to switch to 64bit.. Konrad
