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         const struct bug_entry *bug = NULL;
  68
  69         rcu_read_lock();
  70         list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
  71                 unsigned i;
  72
  73                 bug = mod->bug_table;
  74                 for (i = 0; i < mod->num_bugs; ++i, ++bug)
  75                         if (bugaddr == bug_addr(bug))
  76                                 goto out;
  77         }
  78         bug = NULL;
  79 out:
  80         rcu_read_unlock();
  81
  82         return bug;
  83 }
  84
  85 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
  86                          struct module *mod)
  87 {
  88         char *secstrings;
  89         unsigned int i;
  90
  91         mod->bug_table = NULL;
  92         mod->num_bugs = 0;
  93
  94         /* Find the __bug_table section, if present */
  95         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
  96         for (i = 1; i < hdr->e_shnum; i++) {
  97                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
  98                         continue;
  99                 mod->bug_table = (void *) sechdrs[i].sh_addr;
 100                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
 101                 break;
 102         }
 103
 104         /*
 105          * Strictly speaking this should have a spinlock to protect against
 106          * traversals, but since we only traverse on BUG()s, a spinlock
 107          * could potentially lead to deadlock and thus be counter-productive.
 108          * Thus, this uses RCU to safely manipulate the bug list, since BUG
 109          * must run in non-interruptive state.
 110          */
 111         list_add_rcu(&mod->bug_list, &module_bug_list);
 112 }
 113
 114 void module_bug_cleanup(struct module *mod)
 115 {
 116         list_del_rcu(&mod->bug_list);
 117 }
 118
 119 #else
 120
 121 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
 122 {
 123         return NULL;
 124 }
 125 #endif
 126
 127 const struct bug_entry *find_bug(unsigned long bugaddr)
 128 {
 129         const struct bug_entry *bug;
 130
 131         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
 132                 if (bugaddr == bug_addr(bug))
 133                         return bug;
 134
 135         return module_find_bug(bugaddr);
 136 }
 137
 138 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 139 {
 140         const struct bug_entry *bug;
 141         const char *file;
 142         unsigned line, warning;
 143
 144         if (!is_valid_bugaddr(bugaddr))
 145                 return BUG_TRAP_TYPE_NONE;
 146
 147         bug = find_bug(bugaddr);
 148
 149         file = NULL;
 150         line = 0;
 151         warning = 0;
 152
 153         if (bug) {
 154 #ifdef CONFIG_DEBUG_BUGVERBOSE
 155 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 156                 file = bug->file;
 157 #else
 158                 file = (const char *)bug + bug->file_disp;
 159 #endif
 160                 line = bug->line;
 161 #endif
 162                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
 163         }
 164
 165         if (warning) {
 166                 /* this is a WARN_ON rather than BUG/BUG_ON */
 167                 pr_warn("------------[ cut here ]------------\n");
 168
 169                 if (file)
 170                         pr_warn("WARNING: at %s:%u\n", file, line);
 171                 else
 172                         pr_warn("WARNING: at %p [verbose debug info unavailable]\n",
 173                                 (void *)bugaddr);
 174
 175                 print_modules();
 176                 show_regs(regs);
 177                 print_oops_end_marker();
 178                 /* Just a warning, don't kill lockdep. */
 179                 add_taint(BUG_GET_TAINT(bug), LOCKDEP_STILL_OK);
 180                 return BUG_TRAP_TYPE_WARN;
 181         }
 182
 183         printk(KERN_DEFAULT "------------[ cut here ]------------\n");
 184
 185         if (file)
 186                 pr_crit("kernel BUG at %s:%u!\n", file, line);
 187         else
 188                 pr_crit("Kernel BUG at %p [verbose debug info unavailable]\n",
 189                         (void *)bugaddr);
 190
 191         return BUG_TRAP_TYPE_BUG;
 192 }