On Sun, 17 Sept 2023 at 02:01, Puranjay Mohan <puranjay12@xxxxxxxxx> wrote: > > Implement arch_bpf_stack_walk() for the ARM64 JIT. This will be used > by bpf_throw() to unwind till the program marked as exception boundary and > run the callback with the stack of the main program. > > The prologue generation code has been modified to make the callback > program use the stack of the program marked as exception boundary where > callee-saved registers are already pushed. > > As the bpf_throw function never returns, if it clobbers any callee-saved > registers, they would remain clobbered. So, the prologue of the > exception-boundary program is modified to push R23 and R24 as well, > which the callback will then recover in its epilogue. > > The Procedure Call Standard for the Arm 64-bit Architecture[1] states > that registers r19 to r28 should be saved by the callee. BPF programs on > ARM64 already save all callee-saved registers except r23 and r24. This > patch adds an instruction in prologue of the program to save these > two registers and another instruction in the epilogue to recover them. > > These extra instructions are only added if bpf_throw() used. Otherwise > the emitted prologue/epilogue remains unchanged. > > [1] https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst > > Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx> > --- We need reviews from arm64 JIT experts, but otherwise, given we've discussed this offline as well: Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
