On Thu 2026-08-27 11:14:07, Sebastian Andrzej Siewior wrote: > 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.
I think that it is a matter of taste. I could understand that "(unknown)" might look more obvious to some people. I would still prefer the hashed pointer. It make it consistent with %p handling. Both print addresses in this case. The motivation for the hash in %p is that it is slightly more useful than a static string, e.g. "(address)" or "(pointer)". The hash allows to match the same addresses. It is not 100% reliable but better than nothing. Also the hash makes it more obvious the connection with "no_hash_pointer" option. IMHO, the only drawback is that people might confuse the hash with a real value. But it is easier on 64-bit systems because the higher 32-bits are zeros. Best Regards, Petr
