xref: /openbmc/linux/lib/bug.c (revision 1fa6ac37)
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 static LIST_HEAD(module_bug_list);
59 
60 static 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 
75 int 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 	return 0;
102 }
103 
104 void module_bug_cleanup(struct module *mod)
105 {
106 	list_del(&mod->bug_list);
107 }
108 
109 #else
110 
111 static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
112 {
113 	return NULL;
114 }
115 #endif
116 
117 const struct bug_entry *find_bug(unsigned long bugaddr)
118 {
119 	const struct bug_entry *bug;
120 
121 	for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
122 		if (bugaddr == bug_addr(bug))
123 			return bug;
124 
125 	return module_find_bug(bugaddr);
126 }
127 
128 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
129 {
130 	const struct bug_entry *bug;
131 	const char *file;
132 	unsigned line, warning;
133 
134 	if (!is_valid_bugaddr(bugaddr))
135 		return BUG_TRAP_TYPE_NONE;
136 
137 	bug = find_bug(bugaddr);
138 
139 	printk(KERN_EMERG "------------[ cut here ]------------\n");
140 
141 	file = NULL;
142 	line = 0;
143 	warning = 0;
144 
145 	if (bug) {
146 #ifdef CONFIG_DEBUG_BUGVERBOSE
147 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
148 		file = bug->file;
149 #else
150 		file = (const char *)bug + bug->file_disp;
151 #endif
152 		line = bug->line;
153 #endif
154 		warning = (bug->flags & BUGFLAG_WARNING) != 0;
155 	}
156 
157 	if (warning) {
158 		/* this is a WARN_ON rather than BUG/BUG_ON */
159 		if (file)
160 			printk(KERN_ERR "Badness at %s:%u\n",
161 			       file, line);
162 		else
163 			printk(KERN_ERR "Badness at %p "
164 			       "[verbose debug info unavailable]\n",
165 			       (void *)bugaddr);
166 
167 		show_regs(regs);
168 		add_taint(BUG_GET_TAINT(bug));
169 		return BUG_TRAP_TYPE_WARN;
170 	}
171 
172 	if (file)
173 		printk(KERN_CRIT "kernel BUG at %s:%u!\n",
174 		       file, line);
175 	else
176 		printk(KERN_CRIT "Kernel BUG at %p "
177 		       "[verbose debug info unavailable]\n",
178 		       (void *)bugaddr);
179 
180 	return BUG_TRAP_TYPE_BUG;
181 }
182