Hi,
Unlike most architectures which only handle memory faults/privilege
violations via __ex_table, the MIPS port allows to handle bus error
exceptions via __dbe_table. Unfortunately, the latter table is not
exported to modules, so if a modularized driver needs to probe the address
space for a device it's out of luck.
The following patch implements the kernel part of __dbe_table support. A
separate patch is needed for modutils.
A side effect of the patch is a fix to unhandled bus error exceptions
which happen in the kernel mode. Currently they cause the faulting code
to be reexecuted which results in a hang in an infinite loop. With the
patch applied, the kernel's response is an "Oops" similar to the one
printed when a memory fault happens.
I hope it's fine to apply.
Maciej
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
patch-mips-2.4.5-20010704-dbe-0
diff -up --recursive --new-file linux-mips-2.4.5-20010704.macro/arch/mips/kernel/traps.c linux-mips-2.4.5-20010704/arch/mips/kernel/traps.c
--- linux-mips-2.4.5-20010704.macro/arch/mips/kernel/traps.c Fri Jun 15 04:27:07 2001
+++ linux-mips-2.4.5-20010704/arch/mips/kernel/traps.c Sun Aug 12 17:34:55 2001
@@ -14,6 +14,7 @@
#include <linux/config.h>
#include <linux/init.h>
#include <linux/mm.h>
+#include <linux/module.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
@@ -254,23 +255,59 @@ search_one_table(const struct exception_
return (first == last && first->insn == value) ? first->nextinsn : 0;
}
-#define search_dbe_table(addr) \
- search_one_table(__start___dbe_table, __stop___dbe_table - 1, (addr))
+extern spinlock_t modlist_lock;
+
+static unsigned long
+search_dbe_table(unsigned long addr)
+{
+ unsigned long ret = 0;
+
+#ifndef CONFIG_MODULES
+ /* There is only the kernel to search. */
+ ret = search_one_table(__start___dbe_table, __stop___dbe_table-1, addr);
+ return ret;
+#else
+ unsigned long flags;
+
+ /* The kernel is the last "module" -- no need to treat it special. */
+ struct module *mp;
+
+ spin_lock_irqsave(&modlist_lock, flags);
+ for (mp = module_list; mp != NULL; mp = mp->next) {
+ if (mp->dbe_table_start == NULL || !(mp->flags&(MOD_RUNNING|MOD_INITIALIZING)))
+ continue;
+ ret = search_one_table(mp->dbe_table_start,
+ mp->dbe_table_end - 1, addr);
+ if (ret)
+ break;
+ }
+ spin_unlock_irqrestore(&modlist_lock, flags);
+ return ret;
+#endif
+}
static void default_be_board_handler(struct pt_regs *regs)
{
unsigned long new_epc;
- unsigned long fixup = search_dbe_table(regs->cp0_epc);
+ unsigned long fixup;
- if (fixup) {
- new_epc = fixup_exception(dpf_reg, fixup, regs->cp0_epc);
- regs->cp0_epc = new_epc;
- return;
+ if (!user_mode(regs)) {
+ fixup = search_dbe_table(regs->cp0_epc);
+ if (fixup) {
+ new_epc = fixup_exception(dpf_reg, fixup,
+ regs->cp0_epc);
+ regs->cp0_epc = new_epc;
+ return;
+ }
}
/*
* Assume it would be too dangerous to continue ...
*/
+ printk(KERN_ALERT "%s bus error, epc == %08lx, ra == %08lx\n",
+ (regs->cp0_cause & 4) ? "Data" : "Instruction",
+ regs->cp0_epc, regs->regs[31]);
+ die_if_kernel("Oops", regs);
force_sig(SIGBUS, current);
}
diff -up --recursive --new-file linux-mips-2.4.5-20010704.macro/include/linux/module.h linux-mips-2.4.5-20010704/include/linux/module.h
--- linux-mips-2.4.5-20010704.macro/include/linux/module.h Mon Jul 16 02:13:58 2001
+++ linux-mips-2.4.5-20010704/include/linux/module.h Sun Aug 12 11:22:09 2001
@@ -75,6 +75,10 @@ struct module
void (*cleanup)(void);
const struct exception_table_entry *ex_table_start;
const struct exception_table_entry *ex_table_end;
+#ifdef __mips__
+ const struct exception_table_entry *dbe_table_start;
+ const struct exception_table_entry *dbe_table_end;
+#endif
#ifdef __alpha__
unsigned long gp;
#endif
diff -up --recursive --new-file linux-mips-2.4.5-20010704.macro/kernel/module.c linux-mips-2.4.5-20010704/kernel/module.c
--- linux-mips-2.4.5-20010704.macro/kernel/module.c Thu Jun 14 04:28:48 2001
+++ linux-mips-2.4.5-20010704/kernel/module.c Sun Aug 12 11:24:53 2001
@@ -36,6 +36,11 @@ extern struct module_symbol __stop___ksy
extern const struct exception_table_entry __start___ex_table[];
extern const struct exception_table_entry __stop___ex_table[];
+#ifdef __mips__
+extern const struct exception_table_entry __start___dbe_table[];
+extern const struct exception_table_entry __stop___dbe_table[];
+#endif
+
extern const char __start___kallsyms[] __attribute__ ((weak));
extern const char __stop___kallsyms[] __attribute__ ((weak));
@@ -48,6 +53,10 @@ static struct module kernel_module =
syms: __start___ksymtab,
ex_table_start: __start___ex_table,
ex_table_end: __stop___ex_table,
+#ifdef __mips__
+ dbe_table_start: __start___dbe_table,
+ dbe_table_end: __stop___dbe_table,
+#endif
kallsyms_start: __start___kallsyms,
kallsyms_end: __stop___kallsyms,
};
@@ -436,6 +445,19 @@ sys_init_module(const char *name_user, s
printk(KERN_ERR "init_module: mod->ex_table_* invalid.\n");
goto err2;
}
+#ifdef __mips__
+ if (mod->dbe_table_start > mod->dbe_table_end
+ || (mod->dbe_table_start &&
+ !((unsigned long)mod->dbe_table_start >= ((unsigned long)mod + mod->size_of_struct)
+ && ((unsigned long)mod->dbe_table_end
+ < (unsigned long)mod + mod->size)))
+ || (((unsigned long)mod->dbe_table_start
+ - (unsigned long)mod->dbe_table_end)
+ % sizeof(struct exception_table_entry))) {
+ printk(KERN_ERR "init_module: mod->dbe_table_* invalid.\n");
+ goto err2;
+ }
+#endif
if (mod->flags & ~MOD_AUTOCLEAN) {
printk(KERN_ERR "init_module: mod->flags invalid.\n");
goto err2;
