On Thu, Jul 4, 2024 at 3:24 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> - stack offsets used for spills/fills are allocated as minimal
> stack offsets in whole function and are not used for any other
> purposes;
"minimal stack offset" reads odd to me.
I noticed the same naming convention is used in llvm diff.
imo it's odd there as well.
Maybe say:
llvm grows the stack that in bpf architecture always grows down and
picks the lowest stack offset not used by local variables
and spill/fill.
> Here is how the program looks after verifier processing:
>
> # bpftool prog load ./nocsr.bpf.o /sys/fs/bpf/nocsr-test
> # bpftool prog dump xlated pinned /sys/fs/bpf/nocsr-test
> int test(void * ctx):
> ; int test(void *ctx)
> 0: (bf) r3 = r1 <--------- 3rd printk parameter
> ; __u32 task = bpf_get_smp_processor_id();
> 1: (b4) w0 = 197132 <--------- inlined helper call,
> 2: (bf) r0 = r0 <--------- spill/fill pair removed
Are you using old bpftool or something?
That should have been:
r0 = &(void __percpu *)(r0)
?
> 3: (61) r0 = *(u32 *)(r0 +0) <---------
> ; bpf_printk("ctx=%p, smp=%d", ctx, task);
> 4: (18) r1 = map[id:13][0]+0
> 6: (b7) r2 = 15
> 7: (bf) r4 = r0
> 8: (85) call bpf_trace_printk#-125920
> ; return 0;
> 9: (b7) r0 = 0
> 10: (95) exit
