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/bug.h>
  41 #include <linux/sched.h>
  42
  43 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
  44
  45 #ifdef CONFIG_MODULES
  46 static LIST_HEAD(module_bug_list);
  47
  48 static const struct bug_entry *module_find_bug(unsigned long bugaddr)
  49 {
  50         struct module *mod;
  51
  52         list_for_each_entry(mod, &module_bug_list, bug_list) {
  53                 const struct bug_entry *bug = mod->bug_table;
  54                 unsigned i;
  55
  56                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  57                         if (bugaddr == bug->bug_addr)
  58                                 return bug;
  59         }
  60         return NULL;
  61 }
  62
  63 int module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  64                         struct module *mod)
  65 {
  66         char *secstrings;
  67         unsigned int i;
  68
  69         mod->bug_table = NULL;
  70         mod->num_bugs = 0;
  71
  72         /* Find the __bug_table section, if present */
  73         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  74         for (i = 1; i < hdr->e_shnum; i++) {
  75                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
  76                         continue;
  77                 mod->bug_table = (void *) sechdrs[i].sh_addr;
  78                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
  79                 break;
  80         }
  81
  82         /*
  83          * Strictly speaking this should have a spinlock to protect against
  84          * traversals, but since we only traverse on BUG()s, a spinlock
  85          * could potentially lead to deadlock and thus be counter-productive.
  86          */
  87         list_add(&mod->bug_list, &module_bug_list);
  88
  89         return 0;
  90 }
  91
  92 void module_bug_cleanup(struct module *mod)
  93 {
  94         list_del(&mod->bug_list);
  95 }
  96
  97 #else
  98
  99 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
 100 {
 101         return NULL;
 102 }
 103 #endif
 104
 105 const struct bug_entry *find_bug(unsigned long bugaddr)
 106 {
 107         const struct bug_entry *bug;
 108
 109         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 110                 if (bugaddr == bug->bug_addr)
 111                         return bug;
 112
 113         return module_find_bug(bugaddr);
 114 }
 115
 116 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 117 {
 118         const struct bug_entry *bug;
 119         const char *file;
 120         unsigned line, warning;
 121
 122         if (!is_valid_bugaddr(bugaddr))
 123                 return BUG_TRAP_TYPE_NONE;
 124
 125         bug = find_bug(bugaddr);
 126
 127         printk(KERN_EMERG "------------[ cut here ]------------\n");
 128
 129         file = NULL;
 130         line = 0;
 131         warning = 0;
 132
 133         if (bug) {
 134 #ifdef CONFIG_DEBUG_BUGVERBOSE
 135                 file = bug->file;
 136                 line = bug->line;
 137 #endif
 138                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 139         }
 140
 141         if (warning) {
 142                 /* this is a WARN_ON rather than BUG/BUG_ON */
 143                 if (file)
 144                         printk(KERN_ERR "Badness at %s:%u\n",
 145                                file, line);
 146                 else
 147                         printk(KERN_ERR "Badness at %p "
 148                                "[verbose debug info unavailable]\n",
 149                                (void *)bugaddr);
 150
 151                 show_regs(regs);
 152                 return BUG_TRAP_TYPE_WARN;
 153         }
 154
 155         if (file)
 156                 printk(KERN_CRIT "kernel BUG at %s:%u!\n",
 157                        file, line);
 158         else
 159                 printk(KERN_CRIT "Kernel BUG at %p "
 160                        "[verbose debug info unavailable]\n",
 161                        (void *)bugaddr);
 162
 163         return BUG_TRAP_TYPE_BUG;
 164 }