Re: [tip:perf/kprobes] kprobes: Introduce NOKPROBE_SYMBOL() macro to maintain kprobes blacklist

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2014/05/06 5:48), Tony Luck wrote:
> This patch is in linux-next ("next-20140505") and I see a
> bunch of "Failed to find blacklist" messages when booting
> on ia64:
> 
> Failed to find blacklist 0001013168300000
> Failed to find blacklist 0001013000f0a000
> Failed to find blacklist 000101315f70a000
> Failed to find blacklist 000101324c80a000
> Failed to find blacklist 0001013063f0a000
> Failed to find blacklist 000101327800a000
> Failed to find blacklist 0001013277f0a000
> Failed to find blacklist 000101315a70a000
> Failed to find blacklist 0001013277e0a000
> Failed to find blacklist 000101305a20a000
> Failed to find blacklist 0001013277d0a000
> Failed to find blacklist 00010130bdc0a000
> Failed to find blacklist 00010130dc20a000
> Failed to find blacklist 000101309a00a000
> Failed to find blacklist 0001013277c0a000
> Failed to find blacklist 0001013277b0a000
> Failed to find blacklist 0001013277a0a000
> Failed to find blacklist 000101327790a000
> Failed to find blacklist 000101303140a000
> Failed to find blacklist 0001013a3280a000
> 
> What do these mean?

Ah, I forgot that ia64 has function descriptor :(
That means kprobes initial code has failed to get correct
entry address of the blacklisted functions.

In include/linux/kprobes.h, I defined NOKPROBE_SYMBOL to store
the addresses of blacklisted functions as below,

#define __NOKPROBE_SYMBOL(fname)                        \
static unsigned long __used                             \
        __attribute__((section("_kprobe_blacklist")))   \
        _kbl_addr_##fname = (unsigned long)fname;
#define NOKPROBE_SYMBOL(fname)  __NOKPROBE_SYMBOL(fname)

_kbl_addr_XX stores the address of the function, but on IA64,
it stores the address of function descriptor.

Since those addresses are only used with kallsyms to lookup
function size, I think I should use a macro to store correct
function address instead of the address of function descriptor
on ia64 (and similar arch).
But I'm not sure which macro I should use... Is there any good way
to get the address of function, instead of function descriptor?

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com