microblaze: Support brki rX, 0x18 for user application debugging

This is the first patch which add support for
user application debugging through brki rX, 0x18 vector.

This patch has side effect which also remove security issue
to use brki rX, 0x18 to freeze kernel.

Support for old gdb support via priviledged exception
(brk r0, r0) is still there. It will be remove in future.

Signed-off-by: Michal Simek <monstr@monstr.eu>

2 files changed, 19 insertions, 19 deletions

diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
index 397754cd31c9..5a5cb5842938 100644
--- a/arch/microblaze/kernel/entry.S
+++ b/arch/microblaze/kernel/entry.S
@@ -778,19 +778,22 @@ C_ENTRY(_debug_exception):
 
         addik   r1, r1, -STATE_SAVE_SIZE; /* Make room on the stack.  */
         SAVE_REGS;
+        swi     r17, r1, PTO+PT_R17;
+        swi     r16, r1, PTO+PT_R16;
+        swi     r16, r1, PTO+PT_PC;     /* Save LP */
 
         swi     r0, r1, PTO + PT_MODE; /* Was in user-mode.  */
         lwi     r11, r0, TOPHYS(PER_CPU(ENTRY_SP));
         swi     r11, r1, PTO+PT_R1; /* Store user SP.  */
-2:
+2:      lwi     CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
         tovirt(r1,r1)
 
         set_vms;
-        addi    r5, r0, SIGTRAP              /* send the trap signal */
-        add     r6, r0, CURRENT_TASK; /* Get current task ptr into r11 */
-        addk    r7, r0, r0                   /* 3rd param zero */
-dbtrap_call:    rtbd    r0, send_sig;
+        addik   r5, r1, PTO;
         addik   r15, r0, dbtrap_call;
+dbtrap_call: /* return point for kernel/user entry */
+        rtbd    r0, sw_exception
+        nop
 
         set_bip;                        /*  Ints masked for state restore*/
         lwi     r11, r1, PTO + PT_MODE;
@@ -838,6 +841,8 @@ dbtrap_call:	rtbd	r0, send_sig;
         tophys(r1,r1);
 
         RESTORE_REGS
+        lwi     r17, r1, PTO+PT_R17;
+        lwi     r16, r1, PTO+PT_R16;
         addik   r1, r1, STATE_SAVE_SIZE         /* Clean up stack space.  */
 
 
@@ -854,11 +859,10 @@ dbtrap_call:	rtbd	r0, send_sig;
         tovirt(r1,r1);
 6:
 DBTRAP_return:          /* Make global symbol for debugging */
-        rtbd    r14, 0; /* Instructions to return from an IRQ */
+        rtbd    r16, 0; /* Instructions to return from an IRQ */
         nop;
 
 
-
 ENTRY(_switch_to)
         /* prepare return value */
         addk    r3, r0, CURRENT_TASK
@@ -946,13 +950,6 @@ ENTRY(_switch_to)
 ENTRY(_reset)
         brai    0x70; /* Jump back to FS-boot */
 
-ENTRY(_break)
-        mfs     r5, rmsr
-        swi     r5, r0, 0x250 + TOPHYS(r0_ram)
-        mfs     r5, resr
-        swi     r5, r0, 0x254 + TOPHYS(r0_ram)
-        bri     0
-
         /* These are compiled and loaded into high memory, then
          * copied into place in mach_early_setup */
         .section        .init.ivt, "ax"
@@ -964,12 +961,9 @@ ENTRY(_break)
         nop
         brai    TOPHYS(_user_exception); /* syscall handler */
         brai    TOPHYS(_interrupt);     /* Interrupt handler */
-        brai    TOPHYS(_break);         /* nmi trap handler */
+        brai    TOPHYS(_debug_exception);       /* debug trap handler */
         brai    TOPHYS(_hw_exception_handler);  /* HW exception handler */
 
-        .org    0x60
-        brai    TOPHYS(_debug_exception);       /* debug trap handler*/
-
 .section .rodata,"a"
 #include "syscall_table.S"
 
diff --git a/arch/microblaze/kernel/exceptions.c b/arch/microblaze/kernel/exceptions.c
index 02cbdfe5aa8d..e0c6f8c2bd9d 100644
--- a/arch/microblaze/kernel/exceptions.c
+++ b/arch/microblaze/kernel/exceptions.c
@@ -48,6 +48,12 @@ void die(const char *str, struct pt_regs *fp, long err)
         do_exit(err);
 }
 
+/* for user application debugging */
+void sw_exception(struct pt_regs *regs)
+{
+        _exception(SIGTRAP, regs, TRAP_BRKPT, regs->r16);
+}
+
 void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
 {
         siginfo_t info;
@@ -143,7 +149,7 @@ asmlinkage void full_exception(struct pt_regs *regs, unsigned int type,
 #ifdef CONFIG_MMU
         case MICROBLAZE_PRIVILEGED_EXCEPTION:
                 pr_debug(KERN_WARNING "Privileged exception\n");
-                /* "brk r0,r0" - used as debug breakpoint */
+                /* "brk r0,r0" - used as debug breakpoint - old toolchain */
                 if (get_user(code, (unsigned long *)regs->pc) == 0
                         && code == 0x980c0000) {
                         _exception(SIGTRAP, regs, TRAP_BRKPT, addr);