On Tue, 2024-01-02 at 11:07 -0800, Yonghong Song wrote: > With patch set [1], precision backtracing supports register spill/fill > to/from the stack. The patch [2] allows initial imprecise register spill > with content 0. This is a common case for cpuv3 and lower for > initializing the stack variables with pattern > r1 = 0 > *(u64 *)(r10 - 8) = r1 > and the [2] has demonstrated good verification improvement. > > For cpuv4, the initialization could be > *(u64 *)(r10 - 8) = 0 > The current verifier marks the r10-8 contents with STACK_ZERO. > Similar to [2], let us permit the above insn to behave like > imprecise register spill which can reduce number of verified states. > > I checked cpuv3 and cpuv4 with and without this patch. > There is no change for cpuv3 since '*(u64 *)(r10 - 8) = 0' > is only generated with cpuv4. > [...] > > test_l4lb_noinline and test_l4lb_noinline_dynptr has minor regression, but > pyperf600_bpf_loop and local_storage_bench gets pretty good improvement. > > [1] https://lore.kernel.org/all/20231205184248.1502704-1-andrii@xxxxxxxxxx/ > [2] https://lore.kernel.org/all/20231205184248.1502704-9-andrii@xxxxxxxxxx/ > > Cc: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx> > Cc: Martin KaFai Lau <kafai@xxxxxx> > Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx> Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
