bug.c

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/*
  Generic support for BUG()

  This respects the following config options:

  CONFIG_BUG - emit BUG traps.  Nothing happens without this.
  CONFIG_GENERIC_BUG - enable this code.
  CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
    the containing struct bug_entry for bug_addr and file.
  CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG

  CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
  (though they're generally always on).

  CONFIG_GENERIC_BUG is set by each architecture using this code.

  To use this, your architecture must:

  1. Set up the config options:
     - Enable CONFIG_GENERIC_BUG if CONFIG_BUG

  2. Implement BUG (and optionally BUG_ON, WARN, WARN_ON)
     - Define HAVE_ARCH_BUG
     - Implement BUG() to generate a faulting instruction
     - NOTE: struct bug_entry does not have "file" or "line" entries
       when CONFIG_DEBUG_BUGVERBOSE is not enabled, so you must generate
       the values accordingly.

  3. Implement the trap
     - In the illegal instruction trap handler (typically), verify
       that the fault was in kernel mode, and call report_bug()
     - report_bug() will return whether it was a false alarm, a warning,
       or an actual bug.
     - You must implement the is_valid_bugaddr(bugaddr) callback which
       returns true if the eip is a real kernel address, and it points
       to the expected BUG trap instruction.

    Jeremy Fitzhardinge <[email protected]> 2006
 */
#include <linux/list.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bug.h>
#include <linux/sched.h>

extern const struct bug_entry __start___bug_table[], __stop___bug_table[];

static inline unsigned long bug_addr(const struct bug_entry *bug)
{
#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
    return bug->bug_addr;
#else
    return (unsigned long)bug + bug->bug_addr_disp;
#endif
}

#ifdef CONFIG_MODULES
static LIST_HEAD(module_bug_list);

static const struct bug_entry *module_find_bug(unsigned long bugaddr)
{
    struct module *mod;

    list_for_each_entry(mod, &module_bug_list, bug_list) {
        const struct bug_entry *bug = mod->bug_table;
        unsigned i;

        for (i = 0; i < mod->num_bugs; ++i, ++bug)
            if (bugaddr == bug_addr(bug))
                return bug;
    }
    return NULL;
}

void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
             struct module *mod)
{
    char *secstrings;
    unsigned int i;

    mod->bug_table = NULL;
    mod->num_bugs = 0;

    /* Find the __bug_table section, if present */
    secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
    for (i = 1; i < hdr->e_shnum; i++) {
        if (strcmp(secstrings+sechdrs[i].sh_name, "__bug_table"))
            continue;
        mod->bug_table = (void *) sechdrs[i].sh_addr;
        mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry);
        break;
    }

    /*
     * Strictly speaking this should have a spinlock to protect against
     * traversals, but since we only traverse on BUG()s, a spinlock
     * could potentially lead to deadlock and thus be counter-productive.
     */
    list_add(&mod->bug_list, &module_bug_list);
}

void module_bug_cleanup(struct module *mod)
{
    list_del(&mod->bug_list);
}

#else

static inline const struct bug_entry *module_find_bug(unsigned long bugaddr)
{
    return NULL;
}
#endif

const struct bug_entry *find_bug(unsigned long bugaddr)
{
    const struct bug_entry *bug;

    for (bug = __start___bug_table; bug < __stop___bug_table; ++bug)
        if (bugaddr == bug_addr(bug))
            return bug;

    return module_find_bug(bugaddr);
}

enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
{
    const struct bug_entry *bug;
    const char *file;
    unsigned line, warning;

    if (!is_valid_bugaddr(bugaddr))
        return BUG_TRAP_TYPE_NONE;

    bug = find_bug(bugaddr);

    file = NULL;
    line = 0;
    warning = 0;

    if (bug) {
#ifdef CONFIG_DEBUG_BUGVERBOSE
#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
        file = bug->file;
#else
        file = (const char *)bug + bug->file_disp;
#endif
        line = bug->line;
#endif
        warning = (bug->flags & BUGFLAG_WARNING) != 0;
    }

    if (warning) {
        /* this is a WARN_ON rather than BUG/BUG_ON */
        printk(KERN_WARNING "------------[ cut here ]------------\n");

        if (file)
            printk(KERN_WARNING "WARNING: at %s:%u\n",
                   file, line);
        else
            printk(KERN_WARNING "WARNING: at %p "
                   "[verbose debug info unavailable]\n",
                   (void *)bugaddr);

        print_modules();
        show_regs(regs);
        print_oops_end_marker();
        add_taint(BUG_GET_TAINT(bug));
        return BUG_TRAP_TYPE_WARN;
    }

    printk(KERN_DEFAULT "------------[ cut here ]------------\n");

    if (file)
        printk(KERN_CRIT "kernel BUG at %s:%u!\n",
               file, line);
    else
        printk(KERN_CRIT "Kernel BUG at %p "
               "[verbose debug info unavailable]\n",
               (void *)bugaddr);

    return BUG_TRAP_TYPE_BUG;
}