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>

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

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 */

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__ */

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

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;
 
 

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;

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 */
+};

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;