On Fri, 18 Sep 2020, Ard Biesheuvel wrote: > This series is inspired by Zhei Len's series [0], which updates the > ARM p2v patching code to optionally support p2v relative alignments > of as little as 64 KiB. > > Reducing this alignment is necessary for some specific Huawei boards, > but given that reducing this minimum alignment will make the boot > sequence more robust for all platforms, especially EFI boot, which > no longer relies on the 128 MB masking of the decompressor load address, > but uses firmware memory allocation routines to find a suitable spot > for the decompressed kernel. > > This series is not based on Zhei Len's code, but addresses the same > problem, and takes some feedback given in the review into account: > - use of a MOVW instruction to avoid two adds/adcs sequences when dealing > with the carry on LPAE > - add support for Thumb2 kernels as well > - make the change unconditional - it will bit rot otherwise, and has value > for other platforms as well. > > The first four patches are general cleanup and preparatory changes. > Patch #5 implements the switch to a MOVW instruction without changing > the minimum alignment. > Patch #6 reduces the minimum alignment to 2 MiB. > > Tested on QEMU in ARM/!LPAE, ARM/LPAE, Thumb2/!LPAE and Thumb2/LPAE modes. At this point I think this really ought to be split into a file of its own... and maybe even rewritten in C. Even though I wrote the original code, I no longer understand it without re-investing time into it. But in either cases the whole of head.S would need to have its registers shuffled first to move long lived values away from r0-r3,ip,lr to allow for standard function calls. Nicolas
