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Re: what is the right behavior of copy_to_user(0x0, ..., ...)?

To: Jun Sun <jsun@mvista.com>
Subject: Re: what is the right behavior of copy_to_user(0x0, ..., ...)?
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Fri, 3 May 2002 18:40:00 -0700
Cc: linux-mips <linux-mips@oss.sgi.com>
In-reply-to: <3CD32044.9040109@mvista.com>; from jsun@mvista.com on Fri, May 03, 2002 at 04:41:56PM -0700
References: <3CD3052B.1050400@mvista.com> <20020503162337.A27366@dea.linux-mips.net> <3CD32044.9040109@mvista.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5.1i
On Fri, May 03, 2002 at 04:41:56PM -0700, Jun Sun wrote:

> It appears earlier version of kernel does not have this problem.  I have not 
> fully figured out why.

We didn't handle exceptions in branch delay slots.  Try this patch and
tell me if it helps.

  Ralf

Index: arch/mips/mm/fault.c
===================================================================
RCS file: /home/pub/cvs/linux/arch/mips/mm/fault.c,v
retrieving revision 1.25.2.2
diff -u -r1.25.2.2 fault.c
--- arch/mips/mm/fault.c        16 Jan 2002 03:49:24 -0000      1.25.2.2
+++ arch/mips/mm/fault.c        4 May 2002 01:28:34 -0000
@@ -19,6 +19,7 @@
 #include <linux/smp_lock.h>
 #include <linux/version.h>
 
+#include <asm/branch.h>
 #include <asm/hardirq.h>
 #include <asm/pgalloc.h>
 #include <asm/mmu_context.h>
@@ -77,7 +78,7 @@
        struct vm_area_struct * vma;
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;
-       unsigned long fixup;
+       unsigned long epc, fixup;
        siginfo_t info;
 
        /*
@@ -181,7 +182,8 @@
 
 no_context:
        /* Are we prepared to handle this kernel fault?  */
-       fixup = search_exception_table(regs->cp0_epc);
+       epc = regs->cp0_epc + delay_slot(regs) ? 4 : 0;
+       fixup = search_exception_table(epc);
        if (fixup) {
                long new_epc;
 
Index: arch/mips64/mm/fault.c
===================================================================
RCS file: /home/pub/cvs/linux/arch/mips64/mm/fault.c,v
retrieving revision 1.26.2.6
diff -u -r1.26.2.6 fault.c
--- arch/mips64/mm/fault.c      23 Feb 2002 02:16:42 -0000      1.26.2.6
+++ arch/mips64/mm/fault.c      4 May 2002 01:28:34 -0000
@@ -21,6 +21,7 @@
 #include <linux/smp_lock.h>
 #include <linux/version.h>
 
+#include <asm/branch.h>
 #include <asm/hardirq.h>
 #include <asm/pgalloc.h>
 #include <asm/mmu_context.h>
@@ -103,7 +104,7 @@
        struct vm_area_struct * vma;
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;
-       unsigned long fixup;
+       unsigned long epc, fixup;
        siginfo_t info;
 
 #if 0
@@ -208,7 +209,8 @@
 
 no_context:
        /* Are we prepared to handle this kernel fault?  */
-       fixup = search_exception_table(regs->cp0_epc);
+       epc = regs->cp0_epc + delay_slot(regs) ? 4 : 0;
+       fixup = search_exception_table(epc);
        if (fixup) {
                long new_epc;
 

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