microblaze: Add KGDB support

Kgdb uses brki r16, 0x18 instruction to call
low level _debug_exception function which save
current state to pt_regs and call microblaze_kgdb_break
function. _debug_exception should be called only from
the kernel space. User space calling is not supported
because user application debugging uses different handling.

pt_regs_to_gdb_regs loads additional special registers
which can't be changed

 * Enable KGDB in Kconfig
 * Remove ancient not-tested KGDB support
 * Remove ancient _debug_exception code from entry.S

Only MMU KGDB support is supported.

Signed-off-by: Michal Simek <monstr@monstr.eu>
CC: Jason Wessel <jason.wessel@windriver.com>
CC: John Williams <john.williams@petalogix.com>
CC: Edgar E. Iglesias <edgar.iglesias@petalogix.com>
CC: linux-kernel@vger.kernel.org
Acked-by: Jason Wessel <jason.wessel@windriver.com>

8 files changed, 234 insertions, 81 deletions

diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index a51742190c12..be3855250db6 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -14,6 +14,7 @@ config MICROBLAZE
         select USB_ARCH_HAS_EHCI
         select ARCH_WANT_OPTIONAL_GPIOLIB
         select HAVE_OPROFILE
+        select HAVE_ARCH_KGDB
         select HAVE_DMA_ATTRS
         select HAVE_DMA_API_DEBUG
         select TRACING_SUPPORT
diff --git a/arch/microblaze/include/asm/exceptions.h b/arch/microblaze/include/asm/exceptions.h
index fa0e36657fdd..6479097b802b 100644
--- a/arch/microblaze/include/asm/exceptions.h
+++ b/arch/microblaze/include/asm/exceptions.h
@@ -69,22 +69,6 @@ asmlinkage void full_exception(struct pt_regs *regs, unsigned int type,
 void die(const char *str, struct pt_regs *fp, long err);
 void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr);
 
-#if defined(CONFIG_KGDB)
-void (*debugger)(struct pt_regs *regs);
-int (*debugger_bpt)(struct pt_regs *regs);
-int (*debugger_sstep)(struct pt_regs *regs);
-int (*debugger_iabr_match)(struct pt_regs *regs);
-int (*debugger_dabr_match)(struct pt_regs *regs);
-void (*debugger_fault_handler)(struct pt_regs *regs);
-#else
-#define debugger(regs)                  do { } while (0)
-#define debugger_bpt(regs)              0
-#define debugger_sstep(regs)            0
-#define debugger_iabr_match(regs)       0
-#define debugger_dabr_match(regs)       0
-#define debugger_fault_handler          ((void (*)(struct pt_regs *))0)
-#endif
-
 #endif /*__ASSEMBLY__ */
 #endif /* __KERNEL__ */
 #endif /* _ASM_MICROBLAZE_EXCEPTIONS_H */
diff --git a/arch/microblaze/include/asm/kgdb.h b/arch/microblaze/include/asm/kgdb.h
new file mode 100644
index 000000000000..78b17d40b235
--- /dev/null
+++ b/arch/microblaze/include/asm/kgdb.h
@@ -0,0 +1,28 @@
+#ifdef __KERNEL__
+#ifndef __MICROBLAZE_KGDB_H__
+#define __MICROBLAZE_KGDB_H__
+
+#ifndef __ASSEMBLY__
+
+#define CACHE_FLUSH_IS_SAFE     1
+#define BUFMAX                  2048
+
+/*
+ * 32 32-bit general purpose registers (r0-r31)
+ *  6 32-bit special registers (pc, msr, ear, esr, fsr, btr)
+ * 12 32-bit PVR
+ *   7 32-bit MMU Regs (redr, rpid, rzpr, rtlbx, rtlbsx, rtlblo, rtlbhi)
+ * ------
+ *  57 registers
+ */
+#define NUMREGBYTES     (57 * 4)
+
+#define BREAK_INSTR_SIZE        4
+static inline void arch_kgdb_breakpoint(void)
+{
+        __asm__ __volatile__("brki r16, 0x18;");
+}
+
+#endif /* __ASSEMBLY__ */
+#endif /* __MICROBLAZE_KGDB_H__ */
+#endif /* __KERNEL__ */
diff --git a/arch/microblaze/kernel/Makefile b/arch/microblaze/kernel/Makefile
index d66ddef53c07..5eecc9f1fbd9 100644
--- a/arch/microblaze/kernel/Makefile
+++ b/arch/microblaze/kernel/Makefile
@@ -28,5 +28,6 @@ obj-$(CONFIG_MODULES)		+= microblaze_ksyms.o module.o
 obj-$(CONFIG_MMU)               += misc.o
 obj-$(CONFIG_STACKTRACE)        += stacktrace.o
 obj-$(CONFIG_FUNCTION_TRACER)   += ftrace.o mcount.o
+obj-$(CONFIG_KGDB)              += kgdb.o
 
 obj-y   += entry$(MMU).o
diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
index 5a5cb5842938..304882e56459 100644
--- a/arch/microblaze/kernel/entry.S
+++ b/arch/microblaze/kernel/entry.S
@@ -745,11 +745,8 @@ IRQ_return: /* MS: Make global symbol for debugging */
         nop
 
 /*
- * `Debug' trap
- *  We enter dbtrap in "BIP" (breakpoint) mode.
- *  So we exit the breakpoint mode with an 'rtbd' and proceed with the
- *  original dbtrap.
- *  however, wait to save state first
+ * Debug trap for KGDB. Enter to _debug_exception by brki r16, 0x18
+ * and call handling function with saved pt_regs
  */
 C_ENTRY(_debug_exception):
         /* BIP bit is set on entry, no interrupts can occur */
@@ -759,18 +756,44 @@ C_ENTRY(_debug_exception):
         nop
         andi    r1, r1, MSR_UMS
         bnei    r1, 1f
-        /* Kernel-mode state save.  */
+/* MS: Kernel-mode state save - kgdb */
         lwi     r1, r0, TOPHYS(PER_CPU(ENTRY_SP)); /* Reload kernel stack-ptr*/
-        tophys(r1,r1);
 
-        addik   r1, r1, -STATE_SAVE_SIZE; /* Make room on the stack.  */
+        /* BIP bit is set on entry, no interrupts can occur */
+        addik   r1, r1, CONFIG_KERNEL_BASE_ADDR - CONFIG_KERNEL_START - STATE_SAVE_SIZE;
         SAVE_REGS;
+        /* save all regs to pt_reg structure */
+        swi     r0, r1, PTO+PT_R0;      /* R0 must be saved too */
+        swi     r14, r1, PTO+PT_R14     /* rewrite saved R14 value */
+        swi     r16, r1, PTO+PT_R16
+        swi     r16, r1, PTO+PT_PC; /* PC and r16 are the same */
+        swi     r17, r1, PTO+PT_R17
+        /* save special purpose registers to pt_regs */
+        mfs     r11, rear;
+        swi     r11, r1, PTO+PT_EAR;
+        mfs     r11, resr;
+        swi     r11, r1, PTO+PT_ESR;
+        mfs     r11, rfsr;
+        swi     r11, r1, PTO+PT_FSR;
+
+        /* stack pointer is in physical address at it is decrease
+         * by STATE_SAVE_SIZE but we need to get correct R1 value */
+        addik   r11, r1, CONFIG_KERNEL_START - CONFIG_KERNEL_BASE_ADDR + STATE_SAVE_SIZE;
+        swi     r11, r1, PTO+PT_R1
+        /* MS: r31 - current pointer isn't changed */
+        tovirt(r1,r1)
+#ifdef CONFIG_KGDB
+        addi    r5, r1, PTO /* pass pt_reg address as the first arg */
+        la      r15, r0, dbtrap_call; /* return address */
+        rtbd    r0, microblaze_kgdb_break
+        nop;
+#endif
+        /* MS: Place handler for brki from kernel space if KGDB is OFF.
+         * It is very unlikely that another brki instruction is called. */
+        bri 0
 
-        swi     r1, r1, PTO + PT_MODE;
-        brid    2f;
-        nop;                            /* Fill delay slot */
-1:      /* User-mode state save.  */
-        lwi     r1, r0, TOPHYS(PER_CPU(CURRENT_SAVE)); /* get saved current */
+/* MS: User-mode state save - gdb */
+1:      lwi     r1, r0, TOPHYS(PER_CPU(CURRENT_SAVE)); /* get saved current */
         tophys(r1,r1);
         lwi     r1, r1, TS_THREAD_INFO; /* get the thread info */
         addik   r1, r1, THREAD_SIZE;    /* calculate kernel stack pointer */
@@ -781,36 +804,32 @@ C_ENTRY(_debug_exception):
         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:      lwi     CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
+        lwi     CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
         tovirt(r1,r1)
-
         set_vms;
         addik   r5, r1, PTO;
         addik   r15, r0, dbtrap_call;
-dbtrap_call: /* return point for kernel/user entry */
+dbtrap_call: /* Return point for kernel/user entry + 8 because of rtsd r15, 8 */
         rtbd    r0, sw_exception
         nop
 
-        set_bip;                        /*  Ints masked for state restore*/
+        /* MS: The first instruction for the second part of the gdb/kgdb */
+        set_bip; /* Ints masked for state restore */
         lwi     r11, r1, PTO + PT_MODE;
         bnei    r11, 2f;
-
+/* MS: Return to user space - gdb */
         /* Get current task ptr into r11 */
         lwi     r11, CURRENT_TASK, TS_THREAD_INFO;      /* get thread info */
         lwi     r11, r11, TI_FLAGS;     /* get flags in thread info */
         andi    r11, r11, _TIF_NEED_RESCHED;
         beqi    r11, 5f;
 
-/* Call the scheduler before returning from a syscall/trap. */
-
+        /* Call the scheduler before returning from a syscall/trap. */
         bralid  r15, schedule;  /* Call scheduler */
         nop;                            /* delay slot */
-        /* XXX Is PT_DTRACE handling needed here? */
-        /* XXX m68knommu also checks TASK_STATE & TASK_COUNTER here.  */
 
         /* Maybe handle a signal */
 5:      lwi     r11, CURRENT_TASK, TS_THREAD_INFO;      /* get thread info */
@@ -818,48 +837,37 @@ dbtrap_call: /* return point for kernel/user entry */
         andi    r11, r11, _TIF_SIGPENDING;
         beqi    r11, 1f;                /* Signals to handle, handle them */
 
-/* Handle a signal return; Pending signals should be in r18.  */
-        /* Not all registers are saved by the normal trap/interrupt entry
-           points (for instance, call-saved registers (because the normal
-           C-compiler calling sequence in the kernel makes sure they're
-           preserved), and call-clobbered registers in the case of
-           traps), but signal handlers may want to examine or change the
-           complete register state.  Here we save anything not saved by
-           the normal entry sequence, so that it may be safely restored
-           (in a possibly modified form) after do_signal returns.  */
-
         addik   r5, r1, PTO;            /* Arg 1: struct pt_regs *regs */
         addi  r7, r0, 0;        /* Arg 3: int in_syscall */
         bralid  r15, do_signal; /* Handle any signals */
         add     r6, r0, r0;             /* Arg 2: sigset_t *oldset */
 
-
 /* Finally, return to user state.  */
-1:
-        swi     CURRENT_TASK, r0, PER_CPU(CURRENT_SAVE); /* save current */
+1:      swi     CURRENT_TASK, r0, PER_CPU(CURRENT_SAVE); /* save current */
         VM_OFF;
         tophys(r1,r1);
-
+        /* MS: Restore all regs */
         RESTORE_REGS
         lwi     r17, r1, PTO+PT_R17;
         lwi     r16, r1, PTO+PT_R16;
-        addik   r1, r1, STATE_SAVE_SIZE         /* Clean up stack space.  */
-
-
-        lwi     r1, r1, PT_R1 - PT_SIZE;
-                                        /* Restore user stack pointer. */
-        bri     6f;
+        addik   r1, r1, STATE_SAVE_SIZE  /* Clean up stack space */
+        lwi     r1, r1, PT_R1 - PT_SIZE; /* Restore user stack pointer */
+DBTRAP_return_user: /* MS: Make global symbol for debugging */
+        rtbd    r16, 0; /* MS: Instructions to return from a debug trap */
+        nop;
 
-/* Return to kernel state.  */
+/* MS: Return to kernel state - kgdb */
 2:      VM_OFF;
         tophys(r1,r1);
+        /* MS: Restore all regs */
         RESTORE_REGS
-        addik   r1, r1, STATE_SAVE_SIZE         /* Clean up stack space.  */
-
+        lwi     r14, r1, PTO+PT_R14;
+        lwi     r16, r1, PTO+PT_PC;
+        lwi     r17, r1, PTO+PT_R17;
+        addik   r1, r1, STATE_SAVE_SIZE; /* MS: Clean up stack space */
         tovirt(r1,r1);
-6:
-DBTRAP_return:          /* Make global symbol for debugging */
-        rtbd    r16, 0; /* Instructions to return from an IRQ */
+DBTRAP_return_kernel: /* MS: Make global symbol for debugging */
+        rtbd    r16, 0; /* MS: Instructions to return from a debug trap */
         nop;
 
 
diff --git a/arch/microblaze/kernel/exceptions.c b/arch/microblaze/kernel/exceptions.c
index e0c6f8c2bd9d..b98ee8d0c1cd 100644
--- a/arch/microblaze/kernel/exceptions.c
+++ b/arch/microblaze/kernel/exceptions.c
@@ -59,7 +59,6 @@ void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
         siginfo_t info;
 
         if (kernel_mode(regs)) {
-                debugger(regs);
                 die("Exception in kernel mode", regs, signr);
         }
         info.si_signo = signr;
diff --git a/arch/microblaze/kernel/kgdb.c b/arch/microblaze/kernel/kgdb.c
new file mode 100644
index 000000000000..bfc006b7f2d8
--- /dev/null
+++ b/arch/microblaze/kernel/kgdb.c
@@ -0,0 +1,147 @@
+/*
+ * Microblaze KGDB support
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/kgdb.h>
+#include <linux/kdebug.h>
+#include <linux/irq.h>
+#include <linux/io.h>
+#include <asm/cacheflush.h>
+#include <asm/asm-offsets.h>
+#include <asm/pvr.h>
+
+#define GDB_REG         0
+#define GDB_PC          32
+#define GDB_MSR         33
+#define GDB_EAR         34
+#define GDB_ESR         35
+#define GDB_FSR         36
+#define GDB_BTR         37
+#define GDB_PVR         38
+#define GDB_REDR        50
+#define GDB_RPID        51
+#define GDB_RZPR        52
+#define GDB_RTLBX       53
+#define GDB_RTLBSX      54 /* mfs can't read it */
+#define GDB_RTLBLO      55
+#define GDB_RTLBHI      56
+
+/* keep pvr separately because it is unchangeble */
+struct pvr_s pvr;
+
+void pt_regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
+{
+        int i;
+        unsigned long *pt_regb = (unsigned long *)regs;
+        int temp;
+        /* registers r0 - r31, pc, msr, ear, esr, fsr + do not save pt_mode */
+        for (i = 0; i < (sizeof(struct pt_regs) / 4) - 1; i++)
+                gdb_regs[i] = pt_regb[i];
+
+        /* Branch target register can't be changed */
+        __asm__ __volatile__ ("mfs %0, rbtr;" : "=r"(temp) : );
+        gdb_regs[GDB_BTR] = temp;
+
+        /* pvr part  - we have 11 pvr regs */
+        for (i = 0; i < sizeof(struct pvr_s)/4; i++)
+                gdb_regs[GDB_PVR + i] = pvr.pvr[i];
+
+        /* read special registers - can't be changed */
+        __asm__ __volatile__ ("mfs %0, redr;" : "=r"(temp) : );
+        gdb_regs[GDB_REDR] = temp;
+        __asm__ __volatile__ ("mfs %0, rpid;" : "=r"(temp) : );
+        gdb_regs[GDB_RPID] = temp;
+        __asm__ __volatile__ ("mfs %0, rzpr;" : "=r"(temp) : );
+        gdb_regs[GDB_RZPR] = temp;
+        __asm__ __volatile__ ("mfs %0, rtlbx;" : "=r"(temp) : );
+        gdb_regs[GDB_RTLBX] = temp;
+        __asm__ __volatile__ ("mfs %0, rtlblo;" : "=r"(temp) : );
+        gdb_regs[GDB_RTLBLO] = temp;
+        __asm__ __volatile__ ("mfs %0, rtlbhi;" : "=r"(temp) : );
+        gdb_regs[GDB_RTLBHI] = temp;
+}
+
+void gdb_regs_to_pt_regs(unsigned long *gdb_regs, struct pt_regs *regs)
+{
+        int i;
+        unsigned long *pt_regb = (unsigned long *)regs;
+
+        /* pt_regs and gdb_regs have the same 37 values.
+         * The rest of gdb_regs are unused and can't be changed.
+         * r0 register value can't be changed too. */
+        for (i = 1; i < (sizeof(struct pt_regs) / 4) - 1; i++)
+                pt_regb[i] = gdb_regs[i];
+}
+
+void microblaze_kgdb_break(struct pt_regs *regs)
+{
+        if (kgdb_handle_exception(1, SIGTRAP, 0, regs) != 0)
+                return 0;
+
+        /* Jump over the first arch_kgdb_breakpoint which is barrier to
+         * get kgdb work. The same solution is used for powerpc */
+        if (*(u32 *) (regs->pc) == *(u32 *) (&arch_kgdb_ops.gdb_bpt_instr))
+                regs->pc += BREAK_INSTR_SIZE;
+}
+
+/* untested */
+void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
+{
+        int i;
+        unsigned long *pt_regb = (unsigned long *)(p->thread.regs);
+
+        /* registers r0 - r31, pc, msr, ear, esr, fsr + do not save pt_mode */
+        for (i = 0; i < (sizeof(struct pt_regs) / 4) - 1; i++)
+                gdb_regs[i] = pt_regb[i];
+
+        /* pvr part  - we have 11 pvr regs */
+        for (i = 0; i < sizeof(struct pvr_s)/4; i++)
+                gdb_regs[GDB_PVR + i] = pvr.pvr[i];
+}
+
+void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+{
+        regs->pc = ip;
+}
+
+int kgdb_arch_handle_exception(int vector, int signo, int err_code,
+                               char *remcom_in_buffer, char *remcom_out_buffer,
+                               struct pt_regs *regs)
+{
+        char *ptr;
+        unsigned long address;
+        int cpu = smp_processor_id();
+
+        switch (remcom_in_buffer[0]) {
+        case 'c':
+                /* handle the optional parameter */
+                ptr = &remcom_in_buffer[1];
+                if (kgdb_hex2long(&ptr, &address))
+                        regs->pc = address;
+
+                return 0;
+        }
+        return -1; /* this means that we do not want to exit from the handler */
+}
+
+int kgdb_arch_init(void)
+{
+        get_pvr(&pvr); /* Fill PVR structure */
+        return 0;
+}
+
+void kgdb_arch_exit(void)
+{
+        /* Nothing to do */
+}
+
+/*
+ * Global data
+ */
+struct kgdb_arch arch_kgdb_ops = {
+        .gdb_bpt_instr = {0xba, 0x0c, 0x00, 0x18}, /* brki r16, 0x18 */
+};
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index b224c650a18d..57bd2a09610c 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -37,10 +37,6 @@
 #include <linux/uaccess.h>
 #include <asm/exceptions.h>
 
-#if defined(CONFIG_KGDB)
-int debugger_kernel_faults = 1;
-#endif
-
 static unsigned long pte_misses;        /* updated by do_page_fault() */
 static unsigned long pte_errors;        /* updated by do_page_fault() */
 
@@ -81,10 +77,6 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
         }
 
         /* kernel has accessed a bad area */
-#if defined(CONFIG_KGDB)
-        if (debugger_kernel_faults)
-                debugger(regs);
-#endif
         die("kernel access of bad area", regs, sig);
 }
 
@@ -115,13 +107,6 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
         if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
                 is_write = 0;
 
-#if defined(CONFIG_KGDB)
-        if (debugger_fault_handler && regs->trap == 0x300) {
-                debugger_fault_handler(regs);
-                return;
-        }
-#endif /* CONFIG_KGDB */
-
         if (unlikely(in_atomic() || !mm)) {
                 if (kernel_mode(regs))
                         goto bad_area_nosemaphore;