arm64: Debugging support
This patch adds ptrace, debug monitors and hardware breakpoints support.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
new file mode 100644
index 0000000..0c3ba9f
--- /dev/null
+++ b/arch/arm64/kernel/debug-monitors.c
@@ -0,0 +1,288 @@
+/*
+ * ARMv8 single-step debug support and mdscr context switching.
+ *
+ * Copyright (C) 2012 ARM Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ */
+
+#include <linux/cpu.h>
+#include <linux/debugfs.h>
+#include <linux/hardirq.h>
+#include <linux/init.h>
+#include <linux/ptrace.h>
+#include <linux/stat.h>
+
+#include <asm/debug-monitors.h>
+#include <asm/local.h>
+#include <asm/cputype.h>
+#include <asm/system_misc.h>
+
+/* Low-level stepping controls. */
+#define DBG_MDSCR_SS (1 << 0)
+#define DBG_SPSR_SS (1 << 21)
+
+/* MDSCR_EL1 enabling bits */
+#define DBG_MDSCR_KDE (1 << 13)
+#define DBG_MDSCR_MDE (1 << 15)
+#define DBG_MDSCR_MASK ~(DBG_MDSCR_KDE | DBG_MDSCR_MDE)
+
+/* Determine debug architecture. */
+u8 debug_monitors_arch(void)
+{
+ return read_cpuid(ID_AA64DFR0_EL1) & 0xf;
+}
+
+/*
+ * MDSCR access routines.
+ */
+static void mdscr_write(u32 mdscr)
+{
+ unsigned long flags;
+ local_dbg_save(flags);
+ asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
+ local_dbg_restore(flags);
+}
+
+static u32 mdscr_read(void)
+{
+ u32 mdscr;
+ asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
+ return mdscr;
+}
+
+/*
+ * Allow root to disable self-hosted debug from userspace.
+ * This is useful if you want to connect an external JTAG debugger.
+ */
+static u32 debug_enabled = 1;
+
+static int create_debug_debugfs_entry(void)
+{
+ debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
+ return 0;
+}
+fs_initcall(create_debug_debugfs_entry);
+
+static int __init early_debug_disable(char *buf)
+{
+ debug_enabled = 0;
+ return 0;
+}
+
+early_param("nodebugmon", early_debug_disable);
+
+/*
+ * Keep track of debug users on each core.
+ * The ref counts are per-cpu so we use a local_t type.
+ */
+static DEFINE_PER_CPU(local_t, mde_ref_count);
+static DEFINE_PER_CPU(local_t, kde_ref_count);
+
+void enable_debug_monitors(enum debug_el el)
+{
+ u32 mdscr, enable = 0;
+
+ WARN_ON(preemptible());
+
+ if (local_inc_return(&__get_cpu_var(mde_ref_count)) == 1)
+ enable = DBG_MDSCR_MDE;
+
+ if (el == DBG_ACTIVE_EL1 &&
+ local_inc_return(&__get_cpu_var(kde_ref_count)) == 1)
+ enable |= DBG_MDSCR_KDE;
+
+ if (enable && debug_enabled) {
+ mdscr = mdscr_read();
+ mdscr |= enable;
+ mdscr_write(mdscr);
+ }
+}
+
+void disable_debug_monitors(enum debug_el el)
+{
+ u32 mdscr, disable = 0;
+
+ WARN_ON(preemptible());
+
+ if (local_dec_and_test(&__get_cpu_var(mde_ref_count)))
+ disable = ~DBG_MDSCR_MDE;
+
+ if (el == DBG_ACTIVE_EL1 &&
+ local_dec_and_test(&__get_cpu_var(kde_ref_count)))
+ disable &= ~DBG_MDSCR_KDE;
+
+ if (disable) {
+ mdscr = mdscr_read();
+ mdscr &= disable;
+ mdscr_write(mdscr);
+ }
+}
+
+/*
+ * OS lock clearing.
+ */
+static void clear_os_lock(void *unused)
+{
+ asm volatile("msr mdscr_el1, %0" : : "r" (0));
+ isb();
+ asm volatile("msr oslar_el1, %0" : : "r" (0));
+ isb();
+}
+
+static int __cpuinit os_lock_notify(struct notifier_block *self,
+ unsigned long action, void *data)
+{
+ int cpu = (unsigned long)data;
+ if (action == CPU_ONLINE)
+ smp_call_function_single(cpu, clear_os_lock, NULL, 1);
+ return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata os_lock_nb = {
+ .notifier_call = os_lock_notify,
+};
+
+static int __cpuinit debug_monitors_init(void)
+{
+ /* Clear the OS lock. */
+ smp_call_function(clear_os_lock, NULL, 1);
+ clear_os_lock(NULL);
+
+ /* Register hotplug handler. */
+ register_cpu_notifier(&os_lock_nb);
+ return 0;
+}
+postcore_initcall(debug_monitors_init);
+
+/*
+ * Single step API and exception handling.
+ */
+static void set_regs_spsr_ss(struct pt_regs *regs)
+{
+ unsigned long spsr;
+
+ spsr = regs->pstate;
+ spsr &= ~DBG_SPSR_SS;
+ spsr |= DBG_SPSR_SS;
+ regs->pstate = spsr;
+}
+
+static void clear_regs_spsr_ss(struct pt_regs *regs)
+{
+ unsigned long spsr;
+
+ spsr = regs->pstate;
+ spsr &= ~DBG_SPSR_SS;
+ regs->pstate = spsr;
+}
+
+static int single_step_handler(unsigned long addr, unsigned int esr,
+ struct pt_regs *regs)
+{
+ siginfo_t info;
+
+ /*
+ * If we are stepping a pending breakpoint, call the hw_breakpoint
+ * handler first.
+ */
+ if (!reinstall_suspended_bps(regs))
+ return 0;
+
+ if (user_mode(regs)) {
+ info.si_signo = SIGTRAP;
+ info.si_errno = 0;
+ info.si_code = TRAP_HWBKPT;
+ info.si_addr = (void __user *)instruction_pointer(regs);
+ force_sig_info(SIGTRAP, &info, current);
+
+ /*
+ * ptrace will disable single step unless explicitly
+ * asked to re-enable it. For other clients, it makes
+ * sense to leave it enabled (i.e. rewind the controls
+ * to the active-not-pending state).
+ */
+ user_rewind_single_step(current);
+ } else {
+ /* TODO: route to KGDB */
+ pr_warning("Unexpected kernel single-step exception at EL1\n");
+ /*
+ * Re-enable stepping since we know that we will be
+ * returning to regs.
+ */
+ set_regs_spsr_ss(regs);
+ }
+
+ return 0;
+}
+
+static int __init single_step_init(void)
+{
+ hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
+ TRAP_HWBKPT, "single-step handler");
+ return 0;
+}
+arch_initcall(single_step_init);
+
+/* Re-enable single step for syscall restarting. */
+void user_rewind_single_step(struct task_struct *task)
+{
+ /*
+ * If single step is active for this thread, then set SPSR.SS
+ * to 1 to avoid returning to the active-pending state.
+ */
+ if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
+ set_regs_spsr_ss(task_pt_regs(task));
+}
+
+void user_fastforward_single_step(struct task_struct *task)
+{
+ if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
+ clear_regs_spsr_ss(task_pt_regs(task));
+}
+
+/* Kernel API */
+void kernel_enable_single_step(struct pt_regs *regs)
+{
+ WARN_ON(!irqs_disabled());
+ set_regs_spsr_ss(regs);
+ mdscr_write(mdscr_read() | DBG_MDSCR_SS);
+ enable_debug_monitors(DBG_ACTIVE_EL1);
+}
+
+void kernel_disable_single_step(void)
+{
+ WARN_ON(!irqs_disabled());
+ mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
+ disable_debug_monitors(DBG_ACTIVE_EL1);
+}
+
+int kernel_active_single_step(void)
+{
+ WARN_ON(!irqs_disabled());
+ return mdscr_read() & DBG_MDSCR_SS;
+}
+
+/* ptrace API */
+void user_enable_single_step(struct task_struct *task)
+{
+ set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
+ set_regs_spsr_ss(task_pt_regs(task));
+}
+
+void user_disable_single_step(struct task_struct *task)
+{
+ clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
+}