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
58static LIST_HEAD(module_bug_list);
59
60static const struct bug_entry *module_find_bug(unsigned long bugaddr)
61{
62    struct module *mod;
63
64    list_for_each_entry(mod, &module_bug_list, bug_list) {
65        const struct bug_entry *bug = mod->bug_table;
66        unsigned i;
67
68        for (i = 0; i < mod->num_bugs; ++i, ++bug)
69            if (bugaddr == bug_addr(bug))
70                return bug;
71    }
72    return NULL;
73}
74
75void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
76             struct module *mod)
77{
78    char *secstrings;
79    unsigned int i;
80
81    mod->bug_table = NULL;
82    mod->num_bugs = 0;
83
84    /* Find the __bug_table section, if present */
85    secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
86    for (i = 1; i < hdr->e_shnum; i++) {
87        if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
88            continue;
89        mod->bug_table = (void *) sechdrs[i].sh_addr;
90        mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
91        break;
92    }
93
94    /*
95     * Strictly speaking this should have a spinlock to protect against
96     * traversals, but since we only traverse on BUG()s, a spinlock
97     * could potentially lead to deadlock and thus be counter-productive.
98     */
99    list_add(&mod->bug_list, &module_bug_list);
100}
101
102void module_bug_cleanup(struct module *mod)
103{
104    list_del(&mod->bug_list);
105}
106
107#else
108
109static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
110{
111    return NULL;
112}
113#endif
114
115const struct bug_entry *find_bug(unsigned long bugaddr)
116{
117    const struct bug_entry *bug;
118
119    for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
120        if (bugaddr == bug_addr(bug))
121            return bug;
122
123    return module_find_bug(bugaddr);
124}
125
126enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
127{
128    const struct bug_entry *bug;
129    const char *file;
130    unsigned line, warning;
131
132    if (!is_valid_bugaddr(bugaddr))
133        return BUG_TRAP_TYPE_NONE;
134
135    bug = find_bug(bugaddr);
136
137    file = NULL;
138    line = 0;
139    warning = 0;
140
141    if (bug) {
142#ifdef CONFIG_DEBUG_BUGVERBOSE
143#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
144        file = bug->file;
145#else
146        file = (const char *)bug + bug->file_disp;
147#endif
148        line = bug->line;
149#endif
150        warning = (bug->flags & BUGFLAG_WARNING) != 0;
151    }
152
153    if (warning) {
154        /* this is a WARN_ON rather than BUG/BUG_ON */
155        printk(KERN_WARNING "------------[ cut here ]------------\n");
156
157        if (file)
158            printk(KERN_WARNING "WARNING: at %s:%u\n",
159                   file, line);
160        else
161            printk(KERN_WARNING "WARNING: at %p "
162                   "[verbose debug info unavailable]\n",
163                   (void *)bugaddr);
164
165        print_modules();
166        show_regs(regs);
167        print_oops_end_marker();
168        add_taint(BUG_GET_TAINT(bug));
169        return BUG_TRAP_TYPE_WARN;
170    }
171
172    printk(KERN_EMERG "------------[ cut here ]------------\n");
173
174    if (file)
175        printk(KERN_CRIT "kernel BUG at %s:%u!\n",
176               file, line);
177    else
178        printk(KERN_CRIT "Kernel BUG at %p "
179               "[verbose debug info unavailable]\n",
180               (void *)bugaddr);
181
182    return BUG_TRAP_TYPE_BUG;
183}
184

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