On Wed, Apr 29, 2020 at 5:51 PM Luke Nelson <lukenels@xxxxxxxxxxxxxxxxx> wrote: > > This patch fixes issues with stackframe unwinding and alignment in the > current stack layout for BPF programs on RV32. > > In the current layout, RV32 fp points to the JIT scratch registers, rather > than to the callee-saved registers. This breaks stackframe unwinding, > which expects fp to point just above the saved ra and fp registers. > > This patch fixes the issue by moving the callee-saved registers to be > stored on the top of the stack, pointed to by fp. This satisfies the > assumptions of stackframe unwinding. > > This patch also fixes an issue with the old layout that the stack was > not aligned to 16 bytes. > > Stacktrace from JITed code using the old stack layout: > > [ 12.196249 ] [<c0402200>] walk_stackframe+0x0/0x96 > > Stacktrace using the new stack layout: > > [ 13.062888 ] [<c0402200>] walk_stackframe+0x0/0x96 > [ 13.063028 ] [<c04023c6>] show_stack+0x28/0x32 > [ 13.063253 ] [<a403e778>] bpf_prog_82b916b2dfa00464+0x80/0x908 > [ 13.063417 ] [<c09270b2>] bpf_test_run+0x124/0x39a > [ 13.063553 ] [<c09276c0>] bpf_prog_test_run_skb+0x234/0x448 > [ 13.063704 ] [<c048510e>] __do_sys_bpf+0x766/0x13b4 > [ 13.063840 ] [<c0485d82>] sys_bpf+0xc/0x14 > [ 13.063961 ] [<c04010f0>] ret_from_syscall+0x0/0x2 > > The new code is also simpler to understand and includes an ASCII diagram > of the stack layout. > > Tested on riscv32 QEMU virt machine. > > Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx> Thanks for the fix! Acked-by: Xi Wang <xi.wang@xxxxxxxxx>
