Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT

----- On Mar 27, 2018, at 6:48 PM, Alexei Starovoitov ast@fb.com wrote:

On 3/27/18 2:04 PM, Steven Rostedt wrote:

quoted

+#ifdef CONFIG_BPF_EVENTS
+#define BPF_RAW_TP() . = ALIGN(8);		\

Given that the section consists of a 16-bytes structure elements
on architectures with 8 bytes pointers, this ". = ALIGN(8)" should
be turned into a STRUCT_ALIGN(), especially given that the compiler
is free to up-align the structure on 32 bytes.

This could explain the kasan splat you are experiencing.

Thanks,

Mathieu

quoted

+			 VMLINUX_SYMBOL(__start__bpf_raw_tp) = .;	\
+			 KEEP(*(__bpf_raw_tp_map))			\
+			 VMLINUX_SYMBOL(__stop__bpf_raw_tp) = .;

that looks to be correct, but something wrong with it.

Can you try your mini test with kasan on ?

I'm seeing this crash:
test_stacktrace_[   18.760662] start ffffffff84642438 stop ffffffff84644f60
map_raw_tp:PASS:[   18.761467] i 1 btp->tp cccccccccccccccc
prog_load raw tp[   18.762064] kasan: CONFIG_KASAN_INLINE enabled
 0 nsec
[   18.762704] kasan: GPF could be caused by NULL-ptr deref or user
memory access
[   18.765125] general protection fault: 0000 [#1] SMP KASAN PTI
[   18.765830] Modules linked in:
[   18.778358] Call Trace:
[   18.778674]  bpf_raw_tracepoint_open.isra.27+0x92/0x380

for some reason the start_bpf_raw_tp is off by 8.
Not sure how it works for you.

(gdb) p &__bpf_trace_tp_map_sys_exit
$10 = (struct bpf_raw_event_map *) 0xffffffff84642440
<__bpf_trace_tp_map_sys_exit>

(gdb)  p &__start__bpf_raw_tp
$7 = (<data variable, no debug info> *) 0xffffffff84642438

(gdb)  p (void*)(&__start__bpf_raw_tp)+8
$11 = (void *) 0xffffffff84642440 <__bpf_trace_tp_map_sys_exit>

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com