kernel_optimize_test/arch/mn10300/kernel/switch_to.S
David Howells 5141c46c61 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>
2011-03-18 16:54:32 +00:00

180 lines
4.0 KiB
ArmAsm

###############################################################################
#
# MN10300 Context switch operation
#
# Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
# Written by David Howells (dhowells@redhat.com)
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public Licence
# as published by the Free Software Foundation; either version
# 2 of the Licence, or (at your option) any later version.
#
###############################################################################
#include <linux/sys.h>
#include <linux/linkage.h>
#include <asm/thread_info.h>
#include <asm/cpu-regs.h>
#ifdef CONFIG_SMP
#include <proc/smp-regs.h>
#endif /* CONFIG_SMP */
.text
###############################################################################
#
# struct task_struct *__switch_to(struct thread_struct *prev,
# struct thread_struct *next,
# struct task_struct *prev_task)
#
###############################################################################
ENTRY(__switch_to)
movm [d2,d3,a2,a3,exreg1],(sp)
or EPSW_NMID,epsw
mov (44,sp),d2
mov d0,a0
mov d1,a1
# save prev context
mov __switch_back,d0
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
# switch
mov a2,sp
# load next context
GET_THREAD_INFO a2
mov a2,(__current_ti)
mov (TI_task,a2),a2
mov a2,(__current)
#ifdef CONFIG_MN10300_CURRENT_IN_E2
mov a2,e2
#endif
mov (THREAD_PC,a1),a2
mov d2,d0 # for ret_from_fork
mov d0,a0 # for __switch_to
jmp (a2)
__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 */