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Linux/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_sched();
 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_sched();
 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         lockdep_assert_held(&module_mutex);
 92 
 93         mod->bug_table = NULL;
 94         mod->num_bugs = 0;
 95 
 96         /* Find the __bug_table section, if present */
 97         secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
 98         for (i = 1; i < hdr->e_shnum; i++) {
 99                 if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
100                         continue;
101                 mod->bug_table = (void *) sechdrs[i].sh_addr;
102                 mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
103                 break;
104         }
105 
106         /*
107          * Strictly speaking this should have a spinlock to protect against
108          * traversals, but since we only traverse on BUG()s, a spinlock
109          * could potentially lead to deadlock and thus be counter-productive.
110          * Thus, this uses RCU to safely manipulate the bug list, since BUG
111          * must run in non-interruptive state.
112          */
113         list_add_rcu(&mod->bug_list, &module_bug_list);
114 }
115 
116 void module_bug_cleanup(struct module *mod)
117 {
118         lockdep_assert_held(&module_mutex);
119         list_del_rcu(&mod->bug_list);
120 }
121 
122 #else
123 
124 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
125 {
126         return NULL;
127 }
128 #endif
129 
130 const struct bug_entry *find_bug(unsigned long bugaddr)
131 {
132         const struct bug_entry *bug;
133 
134         for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
135                 if (bugaddr == bug_addr(bug))
136                         return bug;
137 
138         return module_find_bug(bugaddr);
139 }
140 
141 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
142 {
143         const struct bug_entry *bug;
144         const char *file;
145         unsigned line, warning;
146 
147         if (!is_valid_bugaddr(bugaddr))
148                 return BUG_TRAP_TYPE_NONE;
149 
150         bug = find_bug(bugaddr);
151 
152         file = NULL;
153         line = 0;
154         warning = 0;
155 
156         if (bug) {
157 #ifdef CONFIG_DEBUG_BUGVERBOSE
158 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
159                 file = bug->file;
160 #else
161                 file = (const char *)bug + bug->file_disp;
162 #endif
163                 line = bug->line;
164 #endif
165                 warning = (bug->flags & BUGFLAG_WARNING) != 0;
166         }
167 
168         if (warning) {
169                 /* this is a WARN_ON rather than BUG/BUG_ON */
170                 __warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,
171                        NULL);
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 }
185 

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