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_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
   9         the containing struct bug_entry for bug_addr and file.
  10   CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
  11
  12   CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
  13   (though they're generally always on).
  14
  15   CONFIG_GENERIC_BUG is set by each architecture using this code.
  16
  17   To use this, your architecture must:
  18
  19   1. Set up the config options:
  20      - Enable CONFIG_GENERIC_BUG if CONFIG_BUG
  21
  22   2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
  23      - Define HAVE_ARCH_BUG
  24      - Implement BUG() to generate a faulting instruction
  25      - NOTE: struct bug_entry does not have "file" or "line" entries
  26        when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
  27        the values accordingly.
  28
  29   3. Implement the trap
  30      - In the illegal instruction trap handler (typically), verify
  31        that the fault was in kernel mode, and call report_bug()
  32      - report_bug() will return whether it was a false alarm, a warning,
  33        or an actual bug.
  34      - You must implement the is_valid_bugaddr(bugaddr) callback which
  35        returns true if the eip is a real kernel address, and it points
  36        to the expected BUG trap instruction.
  37
  38     Jeremy Fitzhardinge <jeremy@goop.org> 2006
  39  */
  40
  41 #define pr_fmt(fmt) fmt
  42
  43 #include <linux/list.h>
  44 #include <linux/module.h>
  45 #include <linux/kernel.h>
  46 #include <linux/bug.h>
  47 #include <linux/sched.h>
  48
  49 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
  50
  51 static inline unsigned long bug_addr(const struct bug_entry *bug)
  52 {
  53 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  54         return bug->bug_addr;
  55 #else
  56         return (unsigned long)bug + bug->bug_addr_disp;
  57 #endif
  58 }
  59
  60 #ifdef CONFIG_MODULES
  61 /* Updates are protected by module mutex */
  62 static LIST_HEAD(module_bug_list);
  63
  64 static const struct bug_entry *module_find_bug(unsigned long bugaddr)
  65 {
  66         struct module *mod;
  67
  68         list_for_each_entry(mod, &module_bug_list, bug_list) {
  69                 const struct bug_entry *bug = mod->bug_table;
  70                 unsigned i;
  71
  72                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  73                         if (bugaddr == bug_addr(bug))
  74                                 return bug;
  75         }
  76         return NULL;
  77 }
  78
  79 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  80                          struct module *mod)
  81 {
  82         char *secstrings;
  83         unsigned int i;
  84
  85         mod->bug_table = NULL;
  86         mod->num_bugs = 0;
  87
  88         /* Find the __bug_table section, if present */
  89         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  90         for (i = 1; i < hdr->e_shnum; i++) {
  91                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
  92                         continue;
  93                 mod->bug_table = (void *) sechdrs[i].sh_addr;
  94                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
  95                 break;
  96         }
  97
  98         /*
  99          * Strictly speaking this should have a spinlock to protect against
 100          * traversals, but since we only traverse on BUG()s, a spinlock
 101          * could potentially lead to deadlock and thus be counter-productive.
 102          */
 103         list_add(&mod->bug_list, &module_bug_list);
 104 }
 105
 106 void module_bug_cleanup(struct module *mod)
 107 {
 108         list_del(&mod->bug_list);
 109 }
 110
 111 #else
 112
 113 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
 114 {
 115         return NULL;
 116 }
 117 #endif
 118
 119 const struct bug_entry *find_bug(unsigned long bugaddr)
 120 {
 121         const struct bug_entry *bug;
 122
 123         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 124                 if (bugaddr == bug_addr(bug))
 125                         return bug;
 126
 127         return module_find_bug(bugaddr);
 128 }
 129
 130 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 131 {
 132         const struct bug_entry *bug;
 133         const char *file;
 134         unsigned line, warning;
 135
 136         if (!is_valid_bugaddr(bugaddr))
 137                 return BUG_TRAP_TYPE_NONE;
 138
 139         bug = find_bug(bugaddr);
 140
 141         file = NULL;
 142         line = 0;
 143         warning = 0;
 144
 145         if (bug) {
 146 #ifdef CONFIG_DEBUG_BUGVERBOSE
 147 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 148                 file = bug->file;
 149 #else
 150                 file = (const char *)bug + bug->file_disp;
 151 #endif
 152                 line = bug->line;
 153 #endif
 154                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 155         }
 156
 157         if (warning) {
 158                 /* this is a WARN_ON rather than BUG/BUG_ON */
 159                 pr_warn("------------[ cut here ]------------\n");
 160
 161                 if (file)
 162                         pr_warn("WARNING: at %s:%u\n", file, line);
 163                 else
 164                         pr_warn("WARNING: at %p [verbose debug info unavailable]\n",
 165                                 (void *)bugaddr);
 166
 167                 print_modules();
 168                 show_regs(regs);
 169                 print_oops_end_marker();
 170                 /* Just a warning, don't kill lockdep. */
 171                 add_taint(BUG_GET_TAINT(bug), LOCKDEP_STILL_OK);
 172                 return BUG_TRAP_TYPE_WARN;
 173         }
 174
 175         printk(KERN_DEFAULT "------------[ cut here ]------------\n");
 176
 177         if (file)
 178                 pr_crit("kernel BUG at %s:%u!\n", file, line);
 179         else
 180                 pr_crit("Kernel BUG at %p [verbose debug info unavailable]\n",
 181                         (void *)bugaddr);
 182
 183         return BUG_TRAP_TYPE_BUG;
 184 }