[RFC Patch 1/1] Implement hw-breakpoint interfaces for BookE processors
K.Prasad
prasad at linux.vnet.ibm.com
Wed Apr 28 02:40:47 EST 2010
Implement hardware breakpoint interfaces for PowerPC BookE processors
Signed-off-by: K.Prasad <prasad at linux.vnet.ibm.com>
---
arch/powerpc/Kconfig | 2
arch/powerpc/include/asm/cputable.h | 4
arch/powerpc/include/asm/hw_breakpoint_booke.h | 42 +++
arch/powerpc/kernel/Makefile | 4
arch/powerpc/kernel/hw_breakpoint_booke.c | 326 +++++++++++++++++++++++++
arch/powerpc/kernel/ptrace.c | 8
arch/powerpc/kernel/traps.c | 11
include/linux/perf_event.h | 4
8 files changed, 398 insertions(+), 3 deletions(-)
Index: linux-2.6.bookE/arch/powerpc/include/asm/hw_breakpoint_booke.h
===================================================================
--- /dev/null
+++ linux-2.6.bookE/arch/powerpc/include/asm/hw_breakpoint_booke.h
@@ -0,0 +1,42 @@
+#ifndef _I386_HW_BREAKPOINT_H
+#define _I386_HW_BREAKPOINT_H
+
+#ifdef __KERNEL__
+#define __ARCH_HW_BREAKPOINT_H
+
+struct arch_hw_breakpoint {
+ u8 len;
+ unsigned long address;
+ unsigned long type;
+};
+
+#include <linux/kdebug.h>
+#include <linux/percpu.h>
+#include <linux/list.h>
+
+/* Breakpoint length beyond which we should use 'range' breakpoints */
+#define DAC_LEN 8
+
+static inline int hw_breakpoint_slots(int type)
+{
+ return HBP_NUM;
+}
+
+struct perf_event;
+struct pmu;
+
+extern int arch_check_bp_in_kernelspace(struct perf_event *bp);
+extern int arch_validate_hwbkpt_settings(struct perf_event *bp);
+extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+ unsigned long val, void *data);
+extern void hw_breakpoint_handler(struct pt_regs *regs,
+ unsigned long debug_status);
+int arch_install_hw_breakpoint(struct perf_event *bp);
+void arch_uninstall_hw_breakpoint(struct perf_event *bp);
+void hw_breakpoint_pmu_read(struct perf_event *bp);
+
+extern struct pmu perf_ops_bp;
+
+#endif /* __KERNEL__ */
+#endif /* _I386_HW_BREAKPOINT_H */
+
Index: linux-2.6.bookE/arch/powerpc/kernel/hw_breakpoint_booke.c
===================================================================
--- /dev/null
+++ linux-2.6.bookE/arch/powerpc/kernel/hw_breakpoint_booke.c
@@ -0,0 +1,326 @@
+#include <linux/perf_event.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/notifier.h>
+#include <linux/percpu.h>
+#include <linux/kprobes.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/smp.h>
+
+#include <asm/hw_breakpoint_booke.h>
+#include <asm/reg_booke.h>
+#include <asm/reg.h>
+
+/*
+ * Store the 'bp' that caused the hw-breakpoint exception just before we
+ * single-step. Use it to distinguish a single-step exception (due to a
+ * previous hw-breakpoint exception) from a normal one
+ */
+static DEFINE_PER_CPU(struct perf_event *, last_hit_bp);
+
+/*
+ * Save the debug registers to restore them after single-stepping the
+ * instruction that caused the debug exception
+ */
+static DEFINE_PER_CPU(unsigned long, last_hit_dac[2]);
+static DEFINE_PER_CPU(unsigned long, last_hit_dbcr0);
+
+/*
+ * Stores the breakpoints currently in use on each breakpoint address
+ * register for each cpus
+ */
+static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
+
+int hw_breakpoint_weight(struct perf_event *bp)
+{
+ return (bp->attr.bp_len > DAC_LEN) ? 2 : 1;
+}
+
+/*
+ * Install a perf counter breakpoint.
+ *
+ * We seek a free debug address register and use it for this
+ * breakpoint. Eventually we enable it in the debug control register.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+ bool range_bp;
+ int i;
+ struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+ unsigned long dbcr0 = mfspr(SPRN_DBCR0);
+
+ range_bp = (info->len > DAC_LEN) ? true : false;
+ for (i = 0; i < HBP_NUM; i++) {
+ struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
+
+ if (*slot)
+ continue;
+ *slot = bp;
+ mtspr(SPRN_DAC1, info->address);
+ /* Clean the 'type' fields to erase past values */
+ dbcr0 &= ~(DBCR0_DAC2W | DBCR0_DAC2R);
+
+ mtspr(SPRN_DBCR0, dbcr0 |
+ (info->type << (HBP_NUM - i)) | DBCR0_IDM);
+ /*
+ * Use DAC2 register in 'range' mode if the length of the
+ * breakpoint request is 'large'
+ */
+ if (unlikely(range_bp)) {
+ if (i > (HBP_NUM - hw_breakpoint_weight(bp))) {
+ *slot = NULL;
+ mtspr(SPRN_DBCR0, dbcr0);
+ return -EBUSY;
+ }
+ (*slot)++;
+ i++;
+ /*
+ * In 'range' mode use two debug registers, but copy
+ * same breakpoint structure in both slots
+ */
+ *slot = bp;
+ mtspr(SPRN_DAC2, info->address + info->len);
+ mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) |
+ (info->type << (HBP_NUM - i)) | DBCR0_IDM);
+ /* We support only 'inclusive' range for now */
+ mtspr(SPRN_DBCR2, DBCR2_DAC12M);
+ }
+ break;
+ }
+
+/* TODO: Support DVC settings - atleast for user-space breakpoint requests */
+ return 0;
+}
+
+/*
+ * Uninstall the breakpoint contained in the given counter.
+ *
+ * First we search the debug address register it uses and then we disable
+ * it.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+ struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+ int i;
+ unsigned long dbcr0 = mfspr(SPRN_DBCR0);
+
+ for (i = 0; i < HBP_NUM; i++) {
+ struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
+
+ if (*slot != bp)
+ continue;
+ *slot = NULL;
+ dbcr0 &= ~((DBCR0_DAC2W | DBCR0_DAC2R) << i);
+ mtspr(SPRN_DBCR0, dbcr0);
+ if (info->len > DAC_LEN) {
+ (*slot)++;
+ i++;
+ *slot = NULL;
+ dbcr0 &= ~((DBCR0_DAC2W | DBCR0_DAC2R) << i);
+ mtspr(SPRN_DBCR0, dbcr0);
+ }
+ break;
+ }
+
+ if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
+ return;
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+ unsigned long va;
+ struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+ va = info->address;
+ return (va >= TASK_SIZE) && ((va + info->len - 1) >= TASK_SIZE);
+}
+
+static int arch_build_bp_info(struct perf_event *bp)
+{
+ struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+ /* Type */
+ switch (bp->attr.bp_type) {
+ case HW_BREAKPOINT_R:
+ info->type = DBCR0_DAC2R;
+ break;
+ case HW_BREAKPOINT_W:
+ info->type = DBCR0_DAC2W;
+ break;
+ case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
+ info->type = (DBCR0_DAC2W | DBCR0_DAC2R);
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+ int ret;
+
+ ret = arch_build_bp_info(bp);
+ if (ret)
+ return ret;
+ /* TODO: Remove this check when user-space breakpoints are supported */
+ ret = arch_check_bp_in_kernelspace(bp);
+
+ return ret;
+}
+
+/*
+ * Release the user breakpoints used by ptrace
+ */
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+ /* Placeholder for now...required for compilation */
+}
+
+void __kprobes hw_breakpoint_handler(struct pt_regs *regs,
+ unsigned long debug_status)
+{
+ int i, cpu;
+ struct perf_event *bp = NULL;
+ struct arch_hw_breakpoint *bp_info;
+ unsigned long dbcr0;
+
+ /* Disable breakpoints during exception handling */
+ mtmsr(mfmsr() & ~MSR_DE);
+ cpu = smp_processor_id();
+
+ /* Handle all the breakpoints that were triggered */
+ for (i = 0; i < HBP_NUM; ++i) {
+ if ((debug_status & ((DBSR_DAC2R | DBSR_DAC2W) << i)) == 0)
+ continue;
+ /* Clear the debug status register */
+ mtspr(SPRN_DBSR, (DBSR_DAC2R | DBSR_DAC2W) << (HBP_NUM - i));
+
+ /*
+ * The counter may be concurrently released but that can only
+ * occur from a call_rcu() path. We can then safely fetch
+ * the breakpoint, use its callback, touch its counter
+ * while we are in an rcu_read_lock() path.
+ */
+ rcu_read_lock();
+ bp = per_cpu(bp_per_reg[i], cpu);
+ /*
+ * bp can be NULL due to lazy debug register switching
+ * or due to concurrent perf counter removing.
+ */
+ if (!bp) {
+ rcu_read_unlock();
+ return;
+ }
+ }
+
+ bp_info = counter_arch_bp(bp);
+
+ /*
+ * Clear the breakpoint register and single-step the
+ * causative instruction
+ */
+ dbcr0 = per_cpu(last_hit_dbcr0, cpu) = mfspr(SPRN_DBCR0);
+ dbcr0 &= ~((DBCR0_DAC2W | DBCR0_DAC2R) << i);
+
+ /*
+ * Save the debug registers in corresponding per-cpu variables, only to
+ * be restored in the single-step exception handler.
+ */
+ per_cpu(last_hit_dac[0], cpu) = mfspr(SPRN_DAC1);
+ if (unlikely(bp_info->len > DAC_LEN)) {
+ dbcr0 &= ~((DBCR0_DAC2W | DBCR0_DAC2R) << i);
+ per_cpu(last_hit_dac[1], cpu) = mfspr(SPRN_DAC1);
+ }
+ rcu_read_unlock();
+
+ /*
+ * Block-step and single-stepping is not supported
+ * simultaneously for now
+ */
+ dbcr0 &= ~DBCR0_BT;
+ mtspr(SPRN_DBCR0, dbcr0 | DBCR0_IDM | DBCR0_IC);
+ mtmsr(mfmsr() | MSR_DE);
+}
+
+/*
+ * Handle single-step exceptions following a DAC hit
+ */
+int __kprobes single_step_dac_instruction(struct pt_regs *regs)
+{
+ int i, cpu = smp_processor_id();
+ struct arch_hw_breakpoint *bp_info;
+ struct perf_event *bp = per_cpu(last_hit_bp, cpu);
+ unsigned long dbcr0 = mfspr(SPRN_DBCR0);
+
+ /*
+ * Check if we are single-stepping as a result of a
+ * previous HW Breakpoint exception
+ */
+ if (!bp)
+ return NOTIFY_DONE;
+ bp_info = counter_arch_bp(bp);
+ /*
+ * We shall invoke the user-defined callback function in the single
+ * stepping handler to confirm to 'trigger-after-execute' semantics
+ */
+ perf_bp_event(bp, regs);
+
+ /*
+ * Loop through the 'slot's to identify the appropriate DAC register
+ * and restore the breakpoint values
+ */
+ for (i = 0; i < HBP_NUM; i++) {
+ struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
+
+ if (*slot != bp)
+ continue;
+ mtspr(SPRN_DAC1, bp_info->address);
+ dbcr0 &= ~(DBCR0_DAC2W | DBCR0_DAC2R);
+ mtspr(SPRN_DBCR0, dbcr0 |
+ (bp_info->type << (HBP_NUM - i)) | DBCR0_IDM);
+ if (unlikely(bp_info->len > DAC_LEN)) {
+ i++;
+ mtspr(SPRN_DAC2, bp_info->address + bp_info->len);
+ mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) |
+ (bp_info->type << (HBP_NUM - i)) | DBCR0_IDM);
+ mtspr(SPRN_DBCR2, DBCR2_DAC12M);
+ }
+ break;
+ }
+ mtspr(SPRN_DBCR0, dbcr0 | DBCR0_IDM | DBCR0_IC);
+ return NOTIFY_STOP;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_exceptions_notify(
+ struct notifier_block *unused, unsigned long val, void *data)
+{
+ int ret = NOTIFY_DONE;
+
+ if (val == DIE_SSTEP)
+ ret = single_step_dac_instruction(data);
+ return ret;
+}
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+ /* TODO */
+}
Index: linux-2.6.bookE/arch/powerpc/kernel/traps.c
===================================================================
--- linux-2.6.bookE.orig/arch/powerpc/kernel/traps.c
+++ linux-2.6.bookE/arch/powerpc/kernel/traps.c
@@ -57,6 +57,9 @@
#ifdef CONFIG_FSL_BOOKE
#include <asm/dbell.h>
#endif
+#ifdef CONFIG_BOOKE
+#include <asm/hw_breakpoint_booke.h>
+#endif
#if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
int (*__debugger)(struct pt_regs *regs) __read_mostly;
@@ -1151,8 +1154,12 @@ void __kprobes DebugException(struct pt_
}
_exception(SIGTRAP, regs, TRAP_TRACE, regs->nip);
- } else
- handle_debug(regs, debug_status);
+ } else {
+ if (is_kernel_addr(regs->dar))
+ hw_breakpoint_handler(regs, debug_status);
+ else
+ handle_debug(regs, debug_status);
+ }
}
#endif /* CONFIG_PPC_ADV_DEBUG_REGS */
Index: linux-2.6.bookE/arch/powerpc/Kconfig
===================================================================
--- linux-2.6.bookE.orig/arch/powerpc/Kconfig
+++ linux-2.6.bookE/arch/powerpc/Kconfig
@@ -140,7 +140,7 @@ config PPC
select HAVE_SYSCALL_WRAPPERS if PPC64
select GENERIC_ATOMIC64 if PPC32
select HAVE_PERF_EVENTS
- select HAVE_HW_BREAKPOINT if PERF_EVENTS && PPC_BOOK3S_64
+ select HAVE_HW_BREAKPOINT if (PERF_EVENTS && PPC_BOOK3S_64) || BOOKE
config EARLY_PRINTK
bool
Index: linux-2.6.bookE/arch/powerpc/kernel/Makefile
===================================================================
--- linux-2.6.bookE.orig/arch/powerpc/kernel/Makefile
+++ linux-2.6.bookE/arch/powerpc/kernel/Makefile
@@ -34,7 +34,11 @@ obj-y += vdso32/
obj-$(CONFIG_PPC64) += setup_64.o sys_ppc32.o \
signal_64.o ptrace32.o \
paca.o nvram_64.o firmware.o
+ifeq ($(CONFIG_BOOKE),y)
+obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint_booke.o
+else
obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
+endif
obj-$(CONFIG_PPC_BOOK3S_64) += cpu_setup_ppc970.o cpu_setup_pa6t.o
obj64-$(CONFIG_RELOCATABLE) += reloc_64.o
obj-$(CONFIG_PPC_BOOK3E_64) += exceptions-64e.o
Index: linux-2.6.bookE/arch/powerpc/kernel/ptrace.c
===================================================================
--- linux-2.6.bookE.orig/arch/powerpc/kernel/ptrace.c
+++ linux-2.6.bookE/arch/powerpc/kernel/ptrace.c
@@ -787,10 +787,12 @@ int ptrace_set_debugreg(struct task_stru
unsigned long data)
{
#ifdef CONFIG_HAVE_HW_BREAKPOINT
+#ifndef CONFIG_BOOKE
int ret;
struct thread_struct *thread = &(task->thread);
struct perf_event *bp;
struct perf_event_attr attr;
+#endif /* CONFIG_BOOKE */
#endif /* CONFIG_HAVE_HW_BREAKPOINT */
/* For ppc64 we support one DABR and no IABR's at the moment (ppc64).
@@ -821,6 +823,11 @@ int ptrace_set_debugreg(struct task_stru
if (data && !(data & DABR_TRANSLATION))
return -EIO;
#ifdef CONFIG_HAVE_HW_BREAKPOINT
+/*
+ * Temporarily disable use of breakpoint interfaces through ptrace until
+ * user-space breakpoint support is enabled.
+ */
+#ifndef CONFIG_BOOKE
bp = thread->ptrace_bps[0];
if (data == 0) {
if (bp) {
@@ -873,6 +880,7 @@ int ptrace_set_debugreg(struct task_stru
return PTR_ERR(bp);
}
+#endif /* CONFIG_BOOKE */
#endif /* CONFIG_HAVE_HW_BREAKPOINT */
/* Move contents to the DABR register */
Index: linux-2.6.bookE/arch/powerpc/include/asm/cputable.h
===================================================================
--- linux-2.6.bookE.orig/arch/powerpc/include/asm/cputable.h
+++ linux-2.6.bookE/arch/powerpc/include/asm/cputable.h
@@ -512,7 +512,11 @@ static inline int cpu_has_feature(unsign
}
#ifdef CONFIG_HAVE_HW_BREAKPOINT
+#ifdef CONFIG_BOOKE
+#define HBP_NUM 2
+#else
#define HBP_NUM 1
+#endif /* CONFIG_BOOKE */
#endif /* CONFIG_HAVE_HW_BREAKPOINT */
#endif /* !__ASSEMBLY__ */
Index: linux-2.6.bookE/include/linux/perf_event.h
===================================================================
--- linux-2.6.bookE.orig/include/linux/perf_event.h
+++ linux-2.6.bookE/include/linux/perf_event.h
@@ -440,7 +440,11 @@ enum perf_callchain_context {
#endif
#ifdef CONFIG_HAVE_HW_BREAKPOINT
+#ifdef CONFIG_BOOKE
+#include <asm/hw_breakpoint_booke.h>
+#else
#include <asm/hw_breakpoint.h>
+#endif /* CONFIG_BOOKE */
#endif
#include <linux/list.h>
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