On 2026-08-26 17:56:12 [+0200], Petr Mladek wrote:
> On Fri 2026-08-21 17:26:13, Sebastian Andrzej Siewior wrote:
> > The "%ps" format modifier prints the name of the symbol which is more
> > valuable in terms of debugging and does not leak the actual pointer.
> >
> > Without KALLSYMS it will leak the pointer which is not intended. The
> > default policy for pointers is to print a hashed value and not to leak
> > the actual pointer.
> >
> > For !KALLSYMS, print "(unknown)" for any symbol resolution. If hashed
> > pointer are disabled print the bare number.
> >
> > Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
> > ---
> > lib/vsprintf.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 2bc6ef483576c..fcb63f22b1997 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -1008,7 +1008,9 @@ char *symbol_string(char *buf, char *end, void *ptr,
> >
> > return string_nocheck(buf, end, sym, spec);
> > #else
> > - return special_hex_number(buf, end, value, sizeof(void *));
> > + if (unlikely(no_hash_pointers))
> > + return special_hex_number(buf, end, value, sizeof(void *));
> > + return string_nocheck(buf, end, "(unknown)", spec);
> > #endif
> > }
>
> My understanding was that we were going to use
>
> return default_pointer(buf, end, ptr, spec);
>
> It would print the hashed pointer unless no_hash_pointers was set.
> IMHO, it would make the handling of pointer values more consistent.
The difference is that prints "Unknown" instead a value where a name was
expected. Look at this, we have now:
| # cat /proc/timer_list
…
| next_event: 89340000000 nsecs
| set_next_event: (unknown)
| shutdown: (unknown)
| periodic: (unknown)
| oneshot: (unknown)
| oneshot stopped: (unknown)
| event_handler: (unknown)
…
| [ 1.584810] ------------[ cut here ]------------
| [ 1.584811] WARNING: init/main.c:1572 at (unknown), CPU#2: swapper/0/1
| [ 1.584813] Modules linked in:
| [ 1.584816] CPU: 2 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.2.0+ #66
PREEMPT_{RT,(lazy)}
| [ 1.584819] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
2026.05-2 08/06/2026
| [ 1.584820] RIP: 0010:(unknown)
| [ 1.584821] Code: 74 46 e8 89 7c 2d ff e8 14 e5 42 ff e8 df c8 09 ff e8 ba
01 21 ff c7 05 04 2d 75 00 03 00 00 00 e8 8b bf 2b ff e8 56 1b 5c ff <0f> 0b 48
8b 3d bd 41 4a 00 48 85 ff 74 33 e8 33 60 09 ff 85 c0 75
| [ 1.584823] RSP: 0018:ffffc90000023f30 EFLAGS: 00010292
| [ 1.584825] RAX: ffff8881f8d0b000 RBX: ffffffff8216a030 RCX:
ffff888102cae000
| [ 1.584826] RDX: 0000000000000000 RSI: 0000000000000012 RDI:
ffff8881002a3480
| [ 1.584827] RBP: 0000000000000000 R08: ffff8881002a3480 R09:
ffffea00040b2b80
| [ 1.584828] R10: ffff888100041180 R11: ffffc90000023ec0 R12:
ffffc90000023f58
| [ 1.584829] R13: 0000000000000000 R14: 0000000000000000 R15:
0000000000000000
| [ 1.584833] FS: 0000000000000000(0000) GS:ffff8881f8d0b000(0000)
knlGS:0000000000000000
| [ 1.584834] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
| [ 1.584835] CR2: 0000000000000000 CR3: 0000000002e46000 CR4:
00000000003506f0
| [ 1.584837] Call Trace:
| [ 1.584846] <TASK>
| [ 1.584847] (unknown)
| [ 1.584847] ? (unknown)
| [ 1.584849] (unknown)
| [ 1.584850] </TASK>
| [ 1.584850] ---[ end trace 0000000000000000 ]---
while printing a hashed pointer instead would give you:
| # cat /proc/timer_list
…
| next_event: 66384000000 nsecs
| set_next_event: 0000000095ee31e0
| shutdown: 00000000c838001a
| periodic: 000000002e3ab76e
| oneshot: 0000000019def7ac
| oneshot stopped: 00000000c838001a
| event_handler: 0000000053e7a80d
…
| [ 1.498126] ------------[ cut here ]------------
| [ 1.498127] WARNING: init/main.c:1572 at 000000007224a107, CPU#6:
swapper/0/1
| [ 1.498131] Modules linked in:
| [ 1.498135] CPU: 6 UID: 0 PID: 1 Comm: swapper/0 Not tainted 7.2.0+ #68
PREEMPT_{RT,(lazy)}
| [ 1.498138] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
2026.05-2 08/06/2026
| [ 1.498140] RIP: 0010:000000007224a107
| [ 1.498142] Code: 74 46 e8 e9 7c 2d ff e8 74 e5 42 ff e8 3f c9 09 ff e8 1a
02 21 ff c7 05 64 2d 75 00 03 00 00 00 e8 eb bf 2b ff e8 b6 1b 5c ff <0f> 0b 48
8b 3d 1d 42 4a 00 48 85 ff 74 33 e8 93 60 09 ff 85 c0 75
| [ 1.498145] RSP: 0018:ffffc90000023f30 EFLAGS: 00010292
| [ 1.498147] RAX: ffff8881f8e0b000 RBX: ffffffff82169fd0 RCX:
ffff888102d9d2a0
| [ 1.498149] RDX: 0000000000000000 RSI: 000000000000001e RDI:
ffff8881002a3480
| [ 1.498150] RBP: 0000000000000000 R08: ffff8881002a3480 R09:
ffffea00040b6740
| [ 1.498152] R10: ffff888100041180 R11: ffffc90000023ec0 R12:
ffffc90000023f58
| [ 1.498153] R13: 0000000000000000 R14: 0000000000000000 R15:
0000000000000000
| [ 1.498159] FS: 0000000000000000(0000) GS:ffff8881f8e0b000(0000)
knlGS:0000000000000000
| [ 1.498161] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
| [ 1.498162] CR2: 0000000000000000 CR3: 0000000002e46000 CR4:
00000000003506f0
| [ 1.498164] Call Trace:
| [ 1.498171] <TASK>
| [ 1.498172] 00000000cb9bc262
| [ 1.498174] ? 00000000eb5021dd
| [ 1.498176] 00000000ed1a9938
| [ 1.498178] </TASK>
| [ 1.498179] ---[ end trace 0000000000000000 ]---
isn't this confusing? There is no added value in printing some random
numbers. Before this change you would also see "other" random values
with address randomisation. It confuses at best imho.
> Best Regards,
> Petr
Sebastian
