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 #include <linux/list.h>
  41 #include <linux/module.h>
  42 #include <linux/kernel.h>
  43 #include <linux/bug.h>
  44 #include <linux/sched.h>
  45
  46 extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
  47
  48 static inline unsigned long bug_addr(const struct bug_entry *bug)
  49 {
  50 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  51         return bug->bug_addr;
  52 #else
  53         return (unsigned long)bug + bug->bug_addr_disp;
  54 #endif
  55 }
  56
  57 #ifdef CONFIG_MODULES
  58 /* Updates are protected by module mutex */
  59 static LIST_HEAD(module_bug_list);
  60
  61 static const struct bug_entry *module_find_bug(unsigned long bugaddr)
  62 {
  63         struct module *mod;
  64
  65         list_for_each_entry(mod, &module_bug_list, bug_list) {
  66                 const struct bug_entry *bug = mod->bug_table;
  67                 unsigned i;
  68
  69                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  70                         if (bugaddr == bug_addr(bug))
  71                                 return bug;
  72         }
  73         return NULL;
  74 }
  75
  76 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  77                          struct module *mod)
  78 {
  79         char *secstrings;
  80         unsigned int i;
  81
  82         mod->bug_table = NULL;
  83         mod->num_bugs = 0;
  84
  85         /* Find the __bug_table section, if present */
  86         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  87         for (i = 1; i < hdr->e_shnum; i++) {
  88                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
  89                         continue;
  90                 mod->bug_table = (void *) sechdrs[i].sh_addr;
  91                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
  92                 break;
  93         }
  94
  95         /*
  96          * Strictly speaking this should have a spinlock to protect against
  97          * traversals, but since we only traverse on BUG()s, a spinlock
  98          * could potentially lead to deadlock and thus be counter-productive.
  99          */
 100         list_add(&mod->bug_list, &module_bug_list);
 101 }
 102
 103 void module_bug_cleanup(struct module *mod)
 104 {
 105         list_del(&mod->bug_list);
 106 }
 107
 108 #else
 109
 110 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
 111 {
 112         return NULL;
 113 }
 114 #endif
 115
 116 const struct bug_entry *find_bug(unsigned long bugaddr)
 117 {
 118         const struct bug_entry *bug;
 119
 120         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 121                 if (bugaddr == bug_addr(bug))
 122                         return bug;
 123
 124         return module_find_bug(bugaddr);
 125 }
 126
 127 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 128 {
 129         const struct bug_entry *bug;
 130         const char *file;
 131         unsigned line, warning;
 132
 133         if (!is_valid_bugaddr(bugaddr))
 134                 return BUG_TRAP_TYPE_NONE;
 135
 136         bug = find_bug(bugaddr);
 137
 138         file = NULL;
 139         line = 0;
 140         warning = 0;
 141
 142         if (bug) {
 143 #ifdef CONFIG_DEBUG_BUGVERBOSE
 144 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 145                 file = bug->file;
 146 #else
 147                 file = (const char *)bug + bug->file_disp;
 148 #endif
 149                 line = bug->line;
 150 #endif
 151                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 152         }
 153
 154         if (warning) {
 155                 /* this is a WARN_ON rather than BUG/BUG_ON */
 156                 printk(KERN_WARNING "------------[ cut here ]------------\n");
 157
 158                 if (file)
 159                         printk(KERN_WARNING "WARNING: at %s:%u\n",
 160                                file, line);
 161                 else
 162                         printk(KERN_WARNING "WARNING: at %p "
 163                                "[verbose debug info unavailable]\n",
 164                                (void *)bugaddr);
 165
 166                 print_modules();
 167                 show_regs(regs);
 168                 print_oops_end_marker();
 169                 /* Just a warning, don't kill lockdep. */
 170                 add_taint(BUG_GET_TAINT(bug), LOCKDEP_STILL_OK);
 171                 return BUG_TRAP_TYPE_WARN;
 172         }
 173
 174         printk(KERN_DEFAULT "------------[ cut here ]------------\n");
 175
 176         if (file)
 177                 printk(KERN_CRIT "kernel BUG at %s:%u!\n",
 178                        file, line);
 179         else
 180                 printk(KERN_CRIT "Kernel BUG at %p "
 181                        "[verbose debug info unavailable]\n",
 182                        (void *)bugaddr);
 183
 184         return BUG_TRAP_TYPE_BUG;
 185 }