lib/bug.c

   1 /*
   2   Generic support for BUG()
   3
   4   This respects the following config options:
   5
   6   CONFIG_BUG - emit BUG traps.  Nothing happens without this.
   7   CONFIG_GENERIC_BUG - enable this code.
   8   CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
   9
  10   CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
  11   (though they're generally always on).
  12
  13   CONFIG_GENERIC_BUG is set by each architecture using this code.
  14
  15   To use this, your architecture must:
  16
  17   1. Set up the config options:
  18      - Enable CONFIG_GENERIC_BUG if CONFIG_BUG
  19
  20   2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
  21      - Define HAVE_ARCH_BUG
  22      - Implement BUG() to generate a faulting instruction
  23      - NOTE: struct bug_entry does not have "file" or "line" entries
  24        when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
  25        the values accordingly.
  26
  27   3. Implement the trap
  28      - In the illegal instruction trap handler (typically), verify
  29        that the fault was in kernel mode, and call report_bug()
  30      - report_bug() will return whether it was a false alarm, a warning,
  31        or an actual bug.
  32      - You must implement the is_valid_bugaddr(bugaddr) callback which
  33        returns true if the eip is a real kernel address, and it points
  34        to the expected BUG trap instruction.
  35
  36     Jeremy Fitzhardinge <jeremy@goop.org> 2006
  37  */
  38 #include <linux/list.h>
  39 #include <linux/module.h>
  40 #include <linux/kernel.h>
  41 #include <linux/bug.h>
  42 #include <linux/sched.h>
  43
  44 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
  45
  46 #ifdef CONFIG_MODULES
  47 static LIST_HEAD(module_bug_list);
  48
  49 static const struct bug_entry *module_find_bug(unsigned long bugaddr)
  50 {
  51         struct module *mod;
  52
  53         list_for_each_entry(mod, &module_bug_list, bug_list) {
  54                 const struct bug_entry *bug = mod->bug_table;
  55                 unsigned i;
  56
  57                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  58                         if (bugaddr == bug->bug_addr)
  59                                 return bug;
  60         }
  61         return NULL;
  62 }
  63
  64 int module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  65                         struct module *mod)
  66 {
  67         char *secstrings;
  68         unsigned int i;
  69
  70         mod->bug_table = NULL;
  71         mod->num_bugs = 0;
  72
  73         /* Find the __bug_table section, if present */
  74         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  75         for (i = 1; i < hdr->e_shnum; i++) {
  76                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
  77                         continue;
  78                 mod->bug_table = (void *) sechdrs[i].sh_addr;
  79                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
  80                 break;
  81         }
  82
  83         /*
  84          * Strictly speaking this should have a spinlock to protect against
  85          * traversals, but since we only traverse on BUG()s, a spinlock
  86          * could potentially lead to deadlock and thus be counter-productive.
  87          */
  88         list_add(&mod->bug_list, &module_bug_list);
  89
  90         return 0;
  91 }
  92
  93 void module_bug_cleanup(struct module *mod)
  94 {
  95         list_del(&mod->bug_list);
  96 }
  97
  98 #else
  99
 100 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
 101 {
 102         return NULL;
 103 }
 104 #endif
 105
 106 const struct bug_entry *find_bug(unsigned long bugaddr)
 107 {
 108         const struct bug_entry *bug;
 109
 110         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 111                 if (bugaddr == bug->bug_addr)
 112                         return bug;
 113
 114         return module_find_bug(bugaddr);
 115 }
 116
 117 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 118 {
 119         const struct bug_entry *bug;
 120         const char *file;
 121         unsigned line, warning;
 122
 123         if (!is_valid_bugaddr(bugaddr))
 124                 return BUG_TRAP_TYPE_NONE;
 125
 126         bug = find_bug(bugaddr);
 127
 128         printk(KERN_EMERG "------------[ cut here ]------------\n");
 129
 130         file = NULL;
 131         line = 0;
 132         warning = 0;
 133
 134         if (bug) {
 135 #ifdef CONFIG_DEBUG_BUGVERBOSE
 136                 file = bug->file;
 137                 line = bug->line;
 138 #endif
 139                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 140         }
 141
 142         if (warning) {
 143                 /* this is a WARN_ON rather than BUG/BUG_ON */
 144                 if (file)
 145                         printk(KERN_ERR "Badness at %s:%u\n",
 146                                file, line);
 147                 else
 148                         printk(KERN_ERR "Badness at %p "
 149                                "[verbose debug info unavailable]\n",
 150                                (void *)bugaddr);
 151
 152                 show_regs(regs);
 153                 add_taint(TAINT_WARN);
 154                 return BUG_TRAP_TYPE_WARN;
 155         }
 156
 157         if (file)
 158                 printk(KERN_CRIT "kernel BUG at %s:%u!\n",
 159                        file, line);
 160         else
 161                 printk(KERN_CRIT "Kernel BUG at %p "
 162                        "[verbose debug info unavailable]\n",
 163                        (void *)bugaddr);
 164
 165         return BUG_TRAP_TYPE_BUG;
 166 }