wrapper/kallsyms.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
   2  *
   3  * wrapper/kallsyms.c
   4  *
   5  * Wrapper around kallsyms. Using kprobes to get its address when available.
   6  *
   7  * Can we mainline LTTng already so we don't have to waste our time doing this
   8  * kind of hack ?
   9  *
  10  * Copyright (C) 2020 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  11  */
  12
  13 #include <linux/kprobes.h>
  14 #include <linux/module.h>
  15 #include <wrapper/kallsyms.h>
  16
  17 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,7,0))
  18
  19 #ifndef CONFIG_KPROBES
  20 # error "LTTng-modules requires CONFIG_KPROBES on kernels >= 5.7.0"
  21 #endif
  22
  23 static
  24 unsigned long (*kallsyms_lookup_name_sym)(const char *name);
  25
  26 static
  27 int dummy_kprobe_handler(struct kprobe *p, struct pt_regs *regs)
  28 {
  29         return 0;
  30 }
  31
  32 static
  33 unsigned long do_get_kallsyms(void)
  34 {
  35         struct kprobe probe;
  36         int ret;
  37         unsigned long addr;
  38
  39         memset(&probe, 0, sizeof(probe));
  40         probe.pre_handler = dummy_kprobe_handler;
  41         probe.symbol_name = "kallsyms_lookup_name";
  42         ret = register_kprobe(&probe);
  43         if (ret)
  44                 return 0;
  45         addr = (unsigned long)probe.addr;
  46 #ifdef CONFIG_ARM
  47 #ifdef CONFIG_THUMB2_KERNEL
  48         if (addr)
  49                 addr |= 1; /* set bit 0 in address for thumb mode */
  50 #endif
  51 #endif
  52         unregister_kprobe(&probe);
  53         return addr;
  54 }
  55
  56 unsigned long wrapper_kallsyms_lookup_name(const char *name)
  57 {
  58         if (!kallsyms_lookup_name_sym) {
  59                 kallsyms_lookup_name_sym = (void *)do_get_kallsyms();
  60         }
  61         if (kallsyms_lookup_name_sym)
  62                 return kallsyms_lookup_name_sym(name);
  63         else {
  64                 printk_once(KERN_WARNING "LTTng requires kallsyms_lookup_name\n");
  65                 return 0;
  66         }
  67 }
  68 EXPORT_SYMBOL_GPL(wrapper_kallsyms_lookup_name);
  69
  70 #endif