[tip:WIP.x86/alternatives 33/51] arch/x86/kernel/alternative.c:2614: warning: Excess function parameter 'text_poke_array.vec' description in 'smp_text_poke_batch_process'

kernel test robot
2025-03-28T16:13:21Z

tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.x86/alternatives
head: 5c21e894a3e5752ac672af6e542775b3914c6668
commit: 27b765aaed0f436da5462abd28b88bbab253820f [33/51] x86/alternatives: Simplify smp_text_poke_batch_process()
config: i386-buildonly-randconfig-001-20250328 (https://download.01.org/0day-ci/archive/20250329/202503290002.FY3SEEJB-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250329/202503290002.FY3SEEJB-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202503290002.FY3SEEJB-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/alternative.c:2614: warning: Excess function parameter 'text_poke_array.vec' description in 'smp_text_poke_batch_process'
>> arch/x86/kernel/alternative.c:2614: warning: Excess function parameter 'text_poke_array.nr_entries' description in 'smp_text_poke_batch_process'

vim +2614 arch/x86/kernel/alternative.c

17f41571bb2c4a Jiri Kosina 2013-07-23 2591
fd4363fff3d967 Jiri Kosina 2013-07-12 2592 /**
b5cbc1f86f9e4d Ingo Molnar 2025-03-27 2593 * smp_text_poke_batch_process() -- update instructions on live kernel on SMP
27b765aaed0f43 Ingo Molnar 2025-03-27 2594 * @text_poke_array.vec: vector of instructions to patch
27b765aaed0f43 Ingo Molnar 2025-03-27 2595 * @text_poke_array.nr_entries: number of entries in the vector
fd4363fff3d967 Jiri Kosina 2013-07-12 2596 *
fd4363fff3d967 Jiri Kosina 2013-07-12 2597 * Modify multi-byte instruction by using int3 breakpoint on SMP.
ea8596bb2d8d37 Masami Hiramatsu 2013-07-18 2598 * We completely avoid stop_machine() here, and achieve the
ea8596bb2d8d37 Masami Hiramatsu 2013-07-18 2599 * synchronization using int3 breakpoint.
fd4363fff3d967 Jiri Kosina 2013-07-12 2600 *
fd4363fff3d967 Jiri Kosina 2013-07-12 2601 * The way it is done:
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2602 * - For each entry in the vector:
fd4363fff3d967 Jiri Kosina 2013-07-12 2603 * - add a int3 trap to the address that will be patched
fd4363fff3d967 Jiri Kosina 2013-07-12 2604 * - sync cores
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2605 * - For each entry in the vector:
fd4363fff3d967 Jiri Kosina 2013-07-12 2606 * - update all but the first byte of the patched range
fd4363fff3d967 Jiri Kosina 2013-07-12 2607 * - sync cores
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2608 * - For each entry in the vector:
fd4363fff3d967 Jiri Kosina 2013-07-12 2609 * - replace the first byte (int3) by the first byte of
fd4363fff3d967 Jiri Kosina 2013-07-12 2610 * replacing opcode
fd4363fff3d967 Jiri Kosina 2013-07-12 2611 * - sync cores
fd4363fff3d967 Jiri Kosina 2013-07-12 2612 */
27b765aaed0f43 Ingo Molnar 2025-03-27 2613 static void smp_text_poke_batch_process(void)
fd4363fff3d967 Jiri Kosina 2013-07-12 @2614 {
c3d6324f841bab Peter Zijlstra 2019-06-05 2615 unsigned char int3 = INT3_INSN_OPCODE;
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2616 unsigned int i;
c3d6324f841bab Peter Zijlstra 2019-06-05 2617 int do_sync;
9222f606506c5f Jiri Kosina 2018-08-28 2618
9222f606506c5f Jiri Kosina 2018-08-28 2619 lockdep_assert_held(&text_mutex);
9222f606506c5f Jiri Kosina 2018-08-28 2620
efd608fa7403ba Nadav Amit 2022-09-21 2621 /*
f2ad1300a8a6d9 Ingo Molnar 2025-03-27 2622 * Corresponds to the implicit memory barrier in try_get_text_poke_array() to
4dd08bc50f7681 Ingo Molnar 2025-03-27 2623 * ensure reading a non-zero refcount provides up to date text_poke_array data.
efd608fa7403ba Nadav Amit 2022-09-21 2624 */
41e4ceece5913b Eric Dumazet 2025-03-25 2625 for_each_possible_cpu(i)
7cb90cbd1a9fa0 Ingo Molnar 2025-03-27 2626 atomic_set_release(per_cpu_ptr(&int3_refs, i), 1);
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2627
9350a629e839ca Steven Rostedt (Google 2023-05-31 2628) /*
9350a629e839ca Steven Rostedt (Google 2023-05-31 2629) * Function tracing can enable thousands of places that need to be
9350a629e839ca Steven Rostedt (Google 2023-05-31 2630) * updated. This can take quite some time, and with full kernel debugging
9350a629e839ca Steven Rostedt (Google 2023-05-31 2631) * enabled, this could cause the softlockup watchdog to trigger.
9350a629e839ca Steven Rostedt (Google 2023-05-31 2632) * This function gets called every 256 entries added to be patched.
9350a629e839ca Steven Rostedt (Google 2023-05-31 2633) * Call cond_resched() here to make sure that other tasks can get scheduled
9350a629e839ca Steven Rostedt (Google 2023-05-31 2634) * while processing all the functions being patched.
9350a629e839ca Steven Rostedt (Google 2023-05-31 2635) */
9350a629e839ca Steven Rostedt (Google 2023-05-31 2636) cond_resched();
9350a629e839ca Steven Rostedt (Google 2023-05-31 2637)
fd4363fff3d967 Jiri Kosina 2013-07-12 2638 /*
01651324edad9d Peter Zijlstra 2017-07-31 2639 * Corresponding read barrier in int3 notifier for making sure the
27b765aaed0f43 Ingo Molnar 2025-03-27 2640 * text_poke_array.nr_entries and handler are correctly ordered wrt. patching.
fd4363fff3d967 Jiri Kosina 2013-07-12 2641 */
fd4363fff3d967 Jiri Kosina 2013-07-12 2642 smp_wmb();
fd4363fff3d967 Jiri Kosina 2013-07-12 2643
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2644 /*
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2645 * First step: add a int3 trap to the address that will be patched.
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2646 */
27b765aaed0f43 Ingo Molnar 2025-03-27 2647 for (i = 0; i < text_poke_array.nr_entries; i++) {
27b765aaed0f43 Ingo Molnar 2025-03-27 2648 text_poke_array.vec[i].old = *(u8 *)text_poke_addr(&text_poke_array.vec[i]);
27b765aaed0f43 Ingo Molnar 2025-03-27 2649 text_poke(text_poke_addr(&text_poke_array.vec[i]), &int3, INT3_INSN_SIZE);
d769811ca93303 Adrian Hunter 2020-05-12 2650 }
fd4363fff3d967 Jiri Kosina 2013-07-12 2651
5c02ece81848db Peter Zijlstra 2019-10-09 2652 text_poke_sync();
fd4363fff3d967 Jiri Kosina 2013-07-12 2653
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2654 /*
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2655 * Second step: update all but the first byte of the patched range.
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2656 */
27b765aaed0f43 Ingo Molnar 2025-03-27 2657 for (do_sync = 0, i = 0; i < text_poke_array.nr_entries; i++) {
27b765aaed0f43 Ingo Molnar 2025-03-27 2658 u8 old[POKE_MAX_OPCODE_SIZE+1] = { text_poke_array.vec[i].old, };
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2659 u8 _new[POKE_MAX_OPCODE_SIZE+1];
27b765aaed0f43 Ingo Molnar 2025-03-27 2660 const u8 *new = text_poke_array.vec[i].text;
27b765aaed0f43 Ingo Molnar 2025-03-27 2661 int len = text_poke_array.vec[i].len;
97e6c977ccf128 Peter Zijlstra 2019-10-09 2662
76ffa7204b1ad7 Peter Zijlstra 2019-11-11 2663 if (len - INT3_INSN_SIZE > 0) {
d769811ca93303 Adrian Hunter 2020-05-12 2664 memcpy(old + INT3_INSN_SIZE,
27b765aaed0f43 Ingo Molnar 2025-03-27 2665 text_poke_addr(&text_poke_array.vec[i]) + INT3_INSN_SIZE,
d769811ca93303 Adrian Hunter 2020-05-12 2666 len - INT3_INSN_SIZE);
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2667
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2668 if (len == 6) {
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2669 _new[0] = 0x0f;
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2670 memcpy(_new + 1, new, 5);
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2671 new = _new;
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2672 }
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2673
27b765aaed0f43 Ingo Molnar 2025-03-27 2674 text_poke(text_poke_addr(&text_poke_array.vec[i]) + INT3_INSN_SIZE,
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2675 new + INT3_INSN_SIZE,
76ffa7204b1ad7 Peter Zijlstra 2019-11-11 2676 len - INT3_INSN_SIZE);
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2677
c3d6324f841bab Peter Zijlstra 2019-06-05 2678 do_sync++;
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2679 }
d769811ca93303 Adrian Hunter 2020-05-12 2680
d769811ca93303 Adrian Hunter 2020-05-12 2681 /*
d769811ca93303 Adrian Hunter 2020-05-12 2682 * Emit a perf event to record the text poke, primarily to
d769811ca93303 Adrian Hunter 2020-05-12 2683 * support Intel PT decoding which must walk the executable code
d769811ca93303 Adrian Hunter 2020-05-12 2684 * to reconstruct the trace. The flow up to here is:
d769811ca93303 Adrian Hunter 2020-05-12 2685 * - write INT3 byte
d769811ca93303 Adrian Hunter 2020-05-12 2686 * - IPI-SYNC
d769811ca93303 Adrian Hunter 2020-05-12 2687 * - write instruction tail
d769811ca93303 Adrian Hunter 2020-05-12 2688 * At this point the actual control flow will be through the
d769811ca93303 Adrian Hunter 2020-05-12 2689 * INT3 and handler and not hit the old or new instruction.
d769811ca93303 Adrian Hunter 2020-05-12 2690 * Intel PT outputs FUP/TIP packets for the INT3, so the flow
d769811ca93303 Adrian Hunter 2020-05-12 2691 * can still be decoded. Subsequently:
d769811ca93303 Adrian Hunter 2020-05-12 2692 * - emit RECORD_TEXT_POKE with the new instruction
d769811ca93303 Adrian Hunter 2020-05-12 2693 * - IPI-SYNC
d769811ca93303 Adrian Hunter 2020-05-12 2694 * - write first byte
d769811ca93303 Adrian Hunter 2020-05-12 2695 * - IPI-SYNC
d769811ca93303 Adrian Hunter 2020-05-12 2696 * So before the text poke event timestamp, the decoder will see
d769811ca93303 Adrian Hunter 2020-05-12 2697 * either the old instruction flow or FUP/TIP of INT3. After the
d769811ca93303 Adrian Hunter 2020-05-12 2698 * text poke event timestamp, the decoder will see either the
d769811ca93303 Adrian Hunter 2020-05-12 2699 * new instruction flow or FUP/TIP of INT3. Thus decoders can
d769811ca93303 Adrian Hunter 2020-05-12 2700 * use the timestamp as the point at which to modify the
d769811ca93303 Adrian Hunter 2020-05-12 2701 * executable code.
d769811ca93303 Adrian Hunter 2020-05-12 2702 * The old instruction is recorded so that the event can be
d769811ca93303 Adrian Hunter 2020-05-12 2703 * processed forwards or backwards.
d769811ca93303 Adrian Hunter 2020-05-12 2704 */
27b765aaed0f43 Ingo Molnar 2025-03-27 2705 perf_event_text_poke(text_poke_addr(&text_poke_array.vec[i]), old, len, new, len);
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2706 }
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2707
c3d6324f841bab Peter Zijlstra 2019-06-05 2708 if (do_sync) {
fd4363fff3d967 Jiri Kosina 2013-07-12 2709 /*
fd4363fff3d967 Jiri Kosina 2013-07-12 2710 * According to Intel, this core syncing is very likely
fd4363fff3d967 Jiri Kosina 2013-07-12 2711 * not necessary and we'd be safe even without it. But
fd4363fff3d967 Jiri Kosina 2013-07-12 2712 * better safe than sorry (plus there's not only Intel).
fd4363fff3d967 Jiri Kosina 2013-07-12 2713 */
5c02ece81848db Peter Zijlstra 2019-10-09 2714 text_poke_sync();
fd4363fff3d967 Jiri Kosina 2013-07-12 2715 }
fd4363fff3d967 Jiri Kosina 2013-07-12 2716
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2717 /*
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2718 * Third step: replace the first byte (int3) by the first byte of
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2719 * replacing opcode.
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2720 */
27b765aaed0f43 Ingo Molnar 2025-03-27 2721 for (do_sync = 0, i = 0; i < text_poke_array.nr_entries; i++) {
27b765aaed0f43 Ingo Molnar 2025-03-27 2722 u8 byte = text_poke_array.vec[i].text[0];
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2723
27b765aaed0f43 Ingo Molnar 2025-03-27 2724 if (text_poke_array.vec[i].len == 6)
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2725 byte = 0x0f;
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2726
ac0ee0a9560c97 Peter Zijlstra 2023-01-23 2727 if (byte == INT3_INSN_OPCODE)
c3d6324f841bab Peter Zijlstra 2019-06-05 2728 continue;
fd4363fff3d967 Jiri Kosina 2013-07-12 2729
27b765aaed0f43 Ingo Molnar 2025-03-27 2730 text_poke(text_poke_addr(&text_poke_array.vec[i]), &byte, INT3_INSN_SIZE);
c3d6324f841bab Peter Zijlstra 2019-06-05 2731 do_sync++;
c3d6324f841bab Peter Zijlstra 2019-06-05 2732 }
c3d6324f841bab Peter Zijlstra 2019-06-05 2733
c3d6324f841bab Peter Zijlstra 2019-06-05 2734 if (do_sync)
5c02ece81848db Peter Zijlstra 2019-10-09 2735 text_poke_sync();
c3d6324f841bab Peter Zijlstra 2019-06-05 2736
01651324edad9d Peter Zijlstra 2017-07-31 2737 /*
efd608fa7403ba Nadav Amit 2022-09-21 2738 * Remove and wait for refs to be zero.
451283cd40bcec Peter Zijlstra 2025-03-25 2739 *
451283cd40bcec Peter Zijlstra 2025-03-25 2740 * Notably, if after step-3 above the INT3 got removed, then the
451283cd40bcec Peter Zijlstra 2025-03-25 2741 * text_poke_sync() will have serialized against any running INT3
451283cd40bcec Peter Zijlstra 2025-03-25 2742 * handlers and the below spin-wait will not happen.
451283cd40bcec Peter Zijlstra 2025-03-25 2743 *
451283cd40bcec Peter Zijlstra 2025-03-25 2744 * IOW. unless the replacement instruction is INT3, this case goes
451283cd40bcec Peter Zijlstra 2025-03-25 2745 * unused.
01651324edad9d Peter Zijlstra 2017-07-31 2746 */
41e4ceece5913b Eric Dumazet 2025-03-25 2747 for_each_possible_cpu(i) {
7cb90cbd1a9fa0 Ingo Molnar 2025-03-27 2748 atomic_t *refs = per_cpu_ptr(&int3_refs, i);
41e4ceece5913b Eric Dumazet 2025-03-25 2749
41e4ceece5913b Eric Dumazet 2025-03-25 2750 if (unlikely(!atomic_dec_and_test(refs)))
41e4ceece5913b Eric Dumazet 2025-03-25 2751 atomic_cond_read_acquire(refs, !VAL);
41e4ceece5913b Eric Dumazet 2025-03-25 2752 }
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2753 }
c0213b0ac03cf6 Daniel Bristot de Oliveira 2019-06-12 2754

:::::: The code at line 2614 was first introduced by commit
:::::: fd4363fff3d96795d3feb1b3fb48ce590f186bdd x86: Introduce int3 (breakpoint)-based instruction patching

:::::: TO: Jiri Kosina <jkosina@suse.cz>
:::::: CC: H. Peter Anvin <hpa@linux.intel.com>

--
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