Re: [PATCH bpf] bpf: Do more tight ALU bounds tracking

[Hao Luo]

On Fri, Jul 29, 2022 at 3:43 PM Youlin Li <liulin063@xxxxxxxxx> wrote:
>
> In adjust_scalar_min_max_vals(), let 32bit bounds learn from 64bit bounds
> to get more tight bounds tracking. Similar operation can be found in
> reg_set_min_max().
>
> Also, we can now fold reg_bounds_sync() into zext_32_to_64().
>
> Before:
>
>     func#0 @0
>     0: R1=ctx(off=0,imm=0) R10=fp0
>     0: (b7) r0 = 0                        ; R0_w=0
>     1: (b7) r1 = 0                        ; R1_w=0
>     2: (87) r1 = -r1                      ; R1_w=scalar()
>     3: (87) r1 = -r1                      ; R1_w=scalar()
>     4: (c7) r1 s>>= 63                    ; R1_w=scalar(smin=-1,smax=0)
>     5: (07) r1 += 2                       ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0xffffffff))  <--- [*]
>     6: (95) exit
>
> It can be seen that even if the 64bit bounds is clear here, the 32bit
> bounds is still in the state of 'UNKNOWN'.
>
> After:
>
>     func#0 @0
>     0: R1=ctx(off=0,imm=0) R10=fp0
>     0: (b7) r0 = 0                        ; R0_w=0
>     1: (b7) r1 = 0                        ; R1_w=0
>     2: (87) r1 = -r1                      ; R1_w=scalar()
>     3: (87) r1 = -r1                      ; R1_w=scalar()
>     4: (c7) r1 s>>= 63                    ; R1_w=scalar(smin=-1,smax=0)
>     5: (07) r1 += 2                       ; R1_w=scalar(umin=1,umax=2,var_off=(0x0; 0x3))  <--- [*]
>     6: (95) exit
>
> Signed-off-by: Youlin Li <liulin063@xxxxxxxxx>

Looks good to me. Thanks Youlin.

Acked-by: Hao Luo <haoluo@xxxxxxxxxx>

Hao