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
49extern const struct bug_entry __start___bug_table[], __stop___bug_table[];
50
51static 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 */
62static LIST_HEAD(module_bug_list);
63
64static 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;
79out:
80	rcu_read_unlock();
81
82	return bug;
83}
84
85void 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
114void module_bug_cleanup(struct module *mod)
115{
116	list_del_rcu(&mod->bug_list);
117}
118
119#else
120
121static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
122{
123	return NULL;
124}
125#endif
126
127const 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
138enum 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}
193