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>

1 files changed, 57 insertions, 49 deletions

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;