Hi Song, I love your patch! Yet something to improve: [auto build test ERROR on bpf-next/master] url: https://github.com/0day-ci/linux/commits/Song-Liu/bpf-introduce-bpf_get_branch_snapshot/20210831-054455 base: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master config: x86_64-randconfig-a003-20210831 (attached as .config) compiler: gcc-9 (Debian 9.3.0-22) 9.3.0 reproduce (this is a W=1 build): # https://github.com/0day-ci/linux/commit/09548da8ea3e9a75d0d969b18c148ce17ed1c97d git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Song-Liu/bpf-introduce-bpf_get_branch_snapshot/20210831-054455 git checkout 09548da8ea3e9a75d0d969b18c148ce17ed1c97d # save the attached .config to linux build tree mkdir build_dir make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp@xxxxxxxxx> All errors (new ones prefixed by >>): ld: kernel/bpf/trampoline.o: in function `__bpf_prog_enter': >> kernel/bpf/trampoline.c:578: undefined reference to `bpf_perf_branch_snapshot' vim +578 kernel/bpf/trampoline.c 551 552 /* The logic is similar to bpf_prog_run(), but with an explicit 553 * rcu_read_lock() and migrate_disable() which are required 554 * for the trampoline. The macro is split into 555 * call __bpf_prog_enter 556 * call prog->bpf_func 557 * call __bpf_prog_exit 558 * 559 * __bpf_prog_enter returns: 560 * 0 - skip execution of the bpf prog 561 * 1 - execute bpf prog 562 * [2..MAX_U64] - execute bpf prog and record execution time. 563 * This is start time. 564 */ 565 u64 notrace __bpf_prog_enter(struct bpf_prog *prog) 566 __acquires(RCU) 567 { 568 #ifdef CONFIG_PERF_EVENTS 569 /* Calling migrate_disable costs two entries in the LBR. To save 570 * some entries, we call perf_snapshot_branch_stack before 571 * migrate_disable to save some entries. This is OK because we 572 * care about the branch trace before entering the BPF program. 573 * If migrate happens exactly here, there isn't much we can do to 574 * preserve the data. 575 */ 576 if (prog->call_get_branch) 577 static_call(perf_snapshot_branch_stack)( > 578 this_cpu_ptr(&bpf_perf_branch_snapshot)); 579 #endif 580 rcu_read_lock(); 581 migrate_disable(); 582 if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) { 583 inc_misses_counter(prog); 584 return 0; 585 } 586 return bpf_prog_start_time(); 587 } 588 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx
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