MN10300: Emulate single stepping in KGDB on MN10300
Emulate single stepping in KGDB on MN10300 by way of temporary breakpoint
insertion. These breakpoints are never actually seen by KGDB, and will overlay
KGDB's own breakpoints.
The breakpoints are removed by switch_to() and reinstalled on switching back so
that if preemption occurs, the preempting task doesn't hit them (though it will
still hit KGDB's regular breakpoints). If KGDB is reentered for any reason,
then the single step breakpoint is completely erased and must be set again by
the debugger.
We take advantage of the fact that KGDB will effectively halt all other CPUs
whilst this CPU is single-stepping to avoid SMP problems.
If the single-stepping task is preempted and killed without KGDB being
reinvoked, then the breakpoint(s) will be cleared and KGDB will be jumped back
into.
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/arch/mn10300/kernel/switch_to.S b/arch/mn10300/kernel/switch_to.S
index 9074d0f..de3e74f 100644
--- a/arch/mn10300/kernel/switch_to.S
+++ b/arch/mn10300/kernel/switch_to.S
@@ -39,11 +39,17 @@
# save prev context
mov __switch_back,d0
- mov d0,(THREAD_PC,a0)
mov sp,a2
mov a2,(THREAD_SP,a0)
mov a3,(THREAD_A3,a0)
+#ifdef CONFIG_KGDB
+ btst 0xff,(kgdb_single_step)
+ bne __switch_to__lift_sstep_bp
+__switch_to__continue:
+#endif
+ mov d0,(THREAD_PC,a0)
+
mov (THREAD_A3,a1),a3
mov (THREAD_SP,a1),a2
@@ -68,3 +74,106 @@
__switch_back:
and ~EPSW_NMID,epsw
ret [d2,d3,a2,a3,exreg1],32
+
+#ifdef CONFIG_KGDB
+###############################################################################
+#
+# Lift the single-step breakpoints when the task being traced is switched out
+# A0 = prev
+# A1 = next
+#
+###############################################################################
+__switch_to__lift_sstep_bp:
+ add -12,sp
+ mov a0,e4
+ mov a1,e5
+
+ # Clear the single-step flag to prevent us coming this way until we get
+ # switched back in
+ bclr 0xff,(kgdb_single_step)
+
+ # Remove first breakpoint
+ mov (kgdb_sstep_bp_addr),a2
+ cmp 0,a2
+ beq 1f
+ movbu (kgdb_sstep_bp),d0
+ movbu d0,(a2)
+#if defined(CONFIG_MN10300_CACHE_FLUSH_ICACHE) || defined(CONFIG_MN10300_CACHE_INV_ICACHE)
+ mov a2,d0
+ mov a2,d1
+ add 1,d1
+ calls flush_icache_range
+#endif
+1:
+
+ # Remove second breakpoint
+ mov (kgdb_sstep_bp_addr+4),a2
+ cmp 0,a2
+ beq 2f
+ movbu (kgdb_sstep_bp+1),d0
+ movbu d0,(a2)
+#if defined(CONFIG_MN10300_CACHE_FLUSH_ICACHE) || defined(CONFIG_MN10300_CACHE_INV_ICACHE)
+ mov a2,d0
+ mov a2,d1
+ add 1,d1
+ calls flush_icache_range
+#endif
+2:
+
+ # Change the resumption address and return
+ mov __switch_back__reinstall_sstep_bp,d0
+ mov e4,a0
+ mov e5,a1
+ add 12,sp
+ bra __switch_to__continue
+
+###############################################################################
+#
+# Reinstall the single-step breakpoints when the task being traced is switched
+# back in (A1 points to the new thread_struct).
+#
+###############################################################################
+__switch_back__reinstall_sstep_bp:
+ add -12,sp
+ mov a0,e4 # save the return value
+ mov 0xff,d3
+
+ # Reinstall first breakpoint
+ mov (kgdb_sstep_bp_addr),a2
+ cmp 0,a2
+ beq 1f
+ movbu (a2),d0
+ movbu d0,(kgdb_sstep_bp)
+ movbu d3,(a2)
+#if defined(CONFIG_MN10300_CACHE_FLUSH_ICACHE) || defined(CONFIG_MN10300_CACHE_INV_ICACHE)
+ mov a2,d0
+ mov a2,d1
+ add 1,d1
+ calls flush_icache_range
+#endif
+1:
+
+ # Reinstall second breakpoint
+ mov (kgdb_sstep_bp_addr+4),a2
+ cmp 0,a2
+ beq 2f
+ movbu (a2),d0
+ movbu d0,(kgdb_sstep_bp+1)
+ movbu d3,(a2)
+#if defined(CONFIG_MN10300_CACHE_FLUSH_ICACHE) || defined(CONFIG_MN10300_CACHE_INV_ICACHE)
+ mov a2,d0
+ mov a2,d1
+ add 1,d1
+ calls flush_icache_range
+#endif
+2:
+
+ mov d3,(kgdb_single_step)
+
+ # Restore the return value (the previous thread_struct pointer)
+ mov e4,a0
+ mov a0,d0
+ add 12,sp
+ bra __switch_back
+
+#endif /* CONFIG_KGDB */