Root/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
46extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
47
48static 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 */
59static LIST_HEAD(module_bug_list);
60
61static 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
76void 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
103void module_bug_cleanup(struct module *mod)
104{
105    list_del(&mod->bug_list);
106}
107
108#else
109
110static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
111{
112    return NULL;
113}
114#endif
115
116const 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
127enum 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}
186

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