----- On Mar 27, 2018, at 8:00 PM, Alexei Starovoitov ast@xxxxxx wrote:
> On 3/27/18 4:13 PM, Mathieu Desnoyers wrote:
>> ----- On Mar 27, 2018, at 6:48 PM, Alexei Starovoitov ast@xxxxxx wrote:
>>
>>> On 3/27/18 2:04 PM, Steven Rostedt wrote:
>>>>
>>>> +#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.
>
> STRUCT_ALIGN fixed the 'off by 8' issue with kasan,
> but it fails without kasan too.
> For some reason the whole region __start__bpf_raw_tp - __stop__bpf_raw_tp
> comes inited with cccc:
> [ 22.703562] i 1 btp ffffffff8288e530 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.704638] i 2 btp ffffffff8288e540 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.705599] i 3 btp ffffffff8288e550 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.706551] i 4 btp ffffffff8288e560 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.707503] i 5 btp ffffffff8288e570 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.708452] i 6 btp ffffffff8288e580 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.709406] i 7 btp ffffffff8288e590 btp->tp cccccccccccccccc func
> cccccccccccccccc
> [ 22.710368] i 8 btp ffffffff8288e5a0 btp->tp cccccccccccccccc func
> cccccccccccccccc
>
> while gdb shows that everything is good inside vmlinux
> for exactly these addresses.
> Some other linker magic missing?
No, Steven's iteration code is incorrect.
+extern struct bpf_raw_event_map __start__bpf_raw_tp;
+extern struct bpf_raw_event_map __stop__bpf_raw_tp;
That should be:
extern struct bpf_raw_event_map __start__bpf_raw_tp[];
extern struct bpf_raw_event_map __stop__bpf_raw_tp[];
+
+struct bpf_raw_event_map *bpf_find_raw_tracepoint(const char *name)
+{
+ const struct bpf_raw_event_map *btp = &__start__bpf_raw_tp;
const struct bpf_raw_event_map *btp = __start__bpf_raw_tp;
+ int i = 0;
+
+ for (; btp < &__stop__bpf_raw_tp; btp++) {
for (; btp < __stop__bpf_raw_tp; btp++) {
Those start/stop symbols are given their address by the linker
automatically (this is a GNU linker extension). We don't want
pointers to the symbols, but rather the symbols per se to act
as start/stop addresses.
Thanks,
Mathieu
+ i++;
+ if (!strcmp(btp->tp->name, name))
+ return btp;
+ }
+ return NULL;
+}
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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