powerpc: Merge enough to start building in arch/powerpc.

This creates the directory structure under arch/powerpc and a bunch
of Kconfig files.  It does a first-cut merge of arch/powerpc/mm,
arch/powerpc/lib and arch/powerpc/platforms/powermac.  This is enough
to build a 32-bit powermac kernel with ARCH=powerpc.

For now we are getting some unmerged files from arch/ppc/kernel and
arch/ppc/syslib, or arch/ppc64/kernel.  This makes some minor changes
to files in those directories and files outside arch/powerpc.

The boot directory is still not merged.  That's going to be interesting.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 724 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
new file mode 100644
index 000000000000..f5a9d2a84fa1
--- /dev/null
+++ b/arch/powerpc/kernel/process.c
@@ -0,0 +1,724 @@
+/*
+ *  arch/ppc/kernel/process.c
+ *
+ *  Derived from "arch/i386/kernel/process.c"
+ *    Copyright (C) 1995  Linus Torvalds
+ *
+ *  Updated and modified by Cort Dougan (cort@cs.nmt.edu) and
+ *  Paul Mackerras (paulus@cs.anu.edu.au)
+ *
+ *  PowerPC version
+ *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
+ *
+ *  This program is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU General Public License
+ *  as published by the Free Software Foundation; either version
+ *  2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/config.h>
+#include <linux/errno.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/smp_lock.h>
+#include <linux/stddef.h>
+#include <linux/unistd.h>
+#include <linux/ptrace.h>
+#include <linux/slab.h>
+#include <linux/user.h>
+#include <linux/elf.h>
+#include <linux/init.h>
+#include <linux/prctl.h>
+#include <linux/init_task.h>
+#include <linux/module.h>
+#include <linux/kallsyms.h>
+#include <linux/mqueue.h>
+#include <linux/hardirq.h>
+
+#include <asm/pgtable.h>
+#include <asm/uaccess.h>
+#include <asm/system.h>
+#include <asm/io.h>
+#include <asm/processor.h>
+#include <asm/mmu.h>
+#include <asm/prom.h>
+
+extern unsigned long _get_SP(void);
+
+#ifndef CONFIG_SMP
+struct task_struct *last_task_used_math = NULL;
+struct task_struct *last_task_used_altivec = NULL;
+struct task_struct *last_task_used_spe = NULL;
+#endif
+
+static struct fs_struct init_fs = INIT_FS;
+static struct files_struct init_files = INIT_FILES;
+static struct signal_struct init_signals = INIT_SIGNALS(init_signals);
+static struct sighand_struct init_sighand = INIT_SIGHAND(init_sighand);
+struct mm_struct init_mm = INIT_MM(init_mm);
+EXPORT_SYMBOL(init_mm);
+
+/* this is 8kB-aligned so we can get to the thread_info struct
+   at the base of it from the stack pointer with 1 integer instruction. */
+union thread_union init_thread_union
+        __attribute__((__section__(".data.init_task"))) =
+{ INIT_THREAD_INFO(init_task) };
+
+/* initial task structure */
+struct task_struct init_task = INIT_TASK(init_task);
+EXPORT_SYMBOL(init_task);
+
+/* only used to get secondary processor up */
+struct task_struct *current_set[NR_CPUS] = {&init_task, };
+
+/*
+ * Make sure the floating-point register state in the
+ * the thread_struct is up to date for task tsk.
+ */
+void flush_fp_to_thread(struct task_struct *tsk)
+{
+        if (tsk->thread.regs) {
+                /*
+                 * We need to disable preemption here because if we didn't,
+                 * another process could get scheduled after the regs->msr
+                 * test but before we have finished saving the FP registers
+                 * to the thread_struct.  That process could take over the
+                 * FPU, and then when we get scheduled again we would store
+                 * bogus values for the remaining FP registers.
+                 */
+                preempt_disable();
+                if (tsk->thread.regs->msr & MSR_FP) {
+#ifdef CONFIG_SMP
+                        /*
+                         * This should only ever be called for current or
+                         * for a stopped child process.  Since we save away
+                         * the FP register state on context switch on SMP,
+                         * there is something wrong if a stopped child appears
+                         * to still have its FP state in the CPU registers.
+                         */
+                        BUG_ON(tsk != current);
+#endif
+                        giveup_fpu(current);
+                }
+                preempt_enable();
+        }
+}
+
+void enable_kernel_fp(void)
+{
+        WARN_ON(preemptible());
+
+#ifdef CONFIG_SMP
+        if (current->thread.regs && (current->thread.regs->msr & MSR_FP))
+                giveup_fpu(current);
+        else
+                giveup_fpu(NULL);       /* just enables FP for kernel */
+#else
+        giveup_fpu(last_task_used_math);
+#endif /* CONFIG_SMP */
+}
+EXPORT_SYMBOL(enable_kernel_fp);
+
+int dump_task_fpu(struct task_struct *tsk, elf_fpregset_t *fpregs)
+{
+        if (!tsk->thread.regs)
+                return 0;
+        flush_fp_to_thread(current);
+
+        memcpy(fpregs, &tsk->thread.fpr[0], sizeof(*fpregs));
+
+        return 1;
+}
+
+#ifdef CONFIG_ALTIVEC
+void enable_kernel_altivec(void)
+{
+        WARN_ON(preemptible());
+
+#ifdef CONFIG_SMP
+        if (current->thread.regs && (current->thread.regs->msr & MSR_VEC))
+                giveup_altivec(current);
+        else
+                giveup_altivec(NULL);   /* just enable AltiVec for kernel - force */
+#else
+        giveup_altivec(last_task_used_altivec);
+#endif /* CONFIG_SMP */
+}
+EXPORT_SYMBOL(enable_kernel_altivec);
+
+/*
+ * Make sure the VMX/Altivec register state in the
+ * the thread_struct is up to date for task tsk.
+ */
+void flush_altivec_to_thread(struct task_struct *tsk)
+{
+        if (tsk->thread.regs) {
+                preempt_disable();
+                if (tsk->thread.regs->msr & MSR_VEC) {
+#ifdef CONFIG_SMP
+                        BUG_ON(tsk != current);
+#endif
+                        giveup_altivec(current);
+                }
+                preempt_enable();
+        }
+}
+
+int dump_task_altivec(struct pt_regs *regs, elf_vrregset_t *vrregs)
+{
+        flush_altivec_to_thread(current);
+        memcpy(vrregs, &current->thread.vr[0], sizeof(*vrregs));
+        return 1;
+}
+#endif /* CONFIG_ALTIVEC */
+
+#ifdef CONFIG_SPE
+
+void enable_kernel_spe(void)
+{
+        WARN_ON(preemptible());
+
+#ifdef CONFIG_SMP
+        if (current->thread.regs && (current->thread.regs->msr & MSR_SPE))
+                giveup_spe(current);
+        else
+                giveup_spe(NULL);       /* just enable SPE for kernel - force */
+#else
+        giveup_spe(last_task_used_spe);
+#endif /* __SMP __ */
+}
+EXPORT_SYMBOL(enable_kernel_spe);
+
+void flush_spe_to_thread(struct task_struct *tsk)
+{
+        if (tsk->thread.regs) {
+                preempt_disable();
+                if (tsk->thread.regs->msr & MSR_SPE) {
+#ifdef CONFIG_SMP
+                        BUG_ON(tsk != current);
+#endif
+                        giveup_spe(current);
+                }
+                preempt_enable();
+        }
+}
+
+int dump_spe(struct pt_regs *regs, elf_vrregset_t *evrregs)
+{
+        flush_spe_to_thread(current);
+        /* We copy u32 evr[32] + u64 acc + u32 spefscr -> 35 */
+        memcpy(evrregs, &current->thread.evr[0], sizeof(u32) * 35);
+        return 1;
+}
+#endif /* CONFIG_SPE */
+
+static void set_dabr_spr(unsigned long val)
+{
+        mtspr(SPRN_DABR, val);
+}
+
+int set_dabr(unsigned long dabr)
+{
+        int ret = 0;
+
+#ifdef CONFIG_PPC64
+        if (firmware_has_feature(FW_FEATURE_XDABR)) {
+                /* We want to catch accesses from kernel and userspace */
+                unsigned long flags = H_DABRX_KERNEL|H_DABRX_USER;
+                ret = plpar_set_xdabr(dabr, flags);
+        } else if (firmware_has_feature(FW_FEATURE_DABR)) {
+                ret = plpar_set_dabr(dabr);
+        } else
+#endif
+                set_dabr_spr(dabr);
+
+        return ret;
+}
+
+static DEFINE_PER_CPU(unsigned long, current_dabr);
+
+struct task_struct *__switch_to(struct task_struct *prev,
+        struct task_struct *new)
+{
+        struct thread_struct *new_thread, *old_thread;
+        unsigned long flags;
+        struct task_struct *last;
+
+#ifdef CONFIG_SMP
+        /* avoid complexity of lazy save/restore of fpu
+         * by just saving it every time we switch out if
+         * this task used the fpu during the last quantum.
+         *
+         * If it tries to use the fpu again, it'll trap and
+         * reload its fp regs.  So we don't have to do a restore
+         * every switch, just a save.
+         *  -- Cort
+         */
+        if (prev->thread.regs && (prev->thread.regs->msr & MSR_FP))
+                giveup_fpu(prev);
+#ifdef CONFIG_ALTIVEC
+        /*
+         * If the previous thread used altivec in the last quantum
+         * (thus changing altivec regs) then save them.
+         * We used to check the VRSAVE register but not all apps
+         * set it, so we don't rely on it now (and in fact we need
+         * to save & restore VSCR even if VRSAVE == 0).  -- paulus
+         *
+         * On SMP we always save/restore altivec regs just to avoid the
+         * complexity of changing processors.
+         *  -- Cort
+         */
+        if (prev->thread.regs && (prev->thread.regs->msr & MSR_VEC))
+                giveup_altivec(prev);
+        /* Avoid the trap.  On smp this this never happens since
+         * we don't set last_task_used_altivec -- Cort
+         */
+        if (new->thread.regs && last_task_used_altivec == new)
+                new->thread.regs->msr |= MSR_VEC;
+#endif /* CONFIG_ALTIVEC */
+#ifdef CONFIG_SPE
+        /*
+         * If the previous thread used spe in the last quantum
+         * (thus changing spe regs) then save them.
+         *
+         * On SMP we always save/restore spe regs just to avoid the
+         * complexity of changing processors.
+         */
+        if ((prev->thread.regs && (prev->thread.regs->msr & MSR_SPE)))
+                giveup_spe(prev);
+        /* Avoid the trap.  On smp this this never happens since
+         * we don't set last_task_used_spe
+         */
+        if (new->thread.regs && last_task_used_spe == new)
+                new->thread.regs->msr |= MSR_SPE;
+#endif /* CONFIG_SPE */
+#endif /* CONFIG_SMP */
+
+#ifdef CONFIG_PPC64     /* for now */
+        if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr)) {
+                set_dabr(new->thread.dabr);
+                __get_cpu_var(current_dabr) = new->thread.dabr;
+        }
+#endif
+
+        new_thread = &new->thread;
+        old_thread = &current->thread;
+        local_irq_save(flags);
+        last = _switch(old_thread, new_thread);
+
+        local_irq_restore(flags);
+
+        return last;
+}
+
+void show_regs(struct pt_regs * regs)
+{
+        int i, trap;
+
+        printk("NIP: %08lX LR: %08lX SP: %08lX REGS: %p TRAP: %04lx    %s\n",
+               regs->nip, regs->link, regs->gpr[1], regs, regs->trap,
+               print_tainted());
+        printk("MSR: %08lx EE: %01x PR: %01x FP: %01x ME: %01x IR/DR: %01x%01x\n",
+               regs->msr, regs->msr&MSR_EE ? 1 : 0, regs->msr&MSR_PR ? 1 : 0,
+               regs->msr & MSR_FP ? 1 : 0,regs->msr&MSR_ME ? 1 : 0,
+               regs->msr&MSR_IR ? 1 : 0,
+               regs->msr&MSR_DR ? 1 : 0);
+        trap = TRAP(regs);
+        if (trap == 0x300 || trap == 0x600)
+                printk("DAR: %08lX, DSISR: %08lX\n", regs->dar, regs->dsisr);
+        printk("TASK = %p[%d] '%s' THREAD: %p\n",
+               current, current->pid, current->comm, current->thread_info);
+        printk("Last syscall: %ld ", current->thread.last_syscall);
+
+#ifdef CONFIG_SMP
+        printk(" CPU: %d", smp_processor_id());
+#endif /* CONFIG_SMP */
+
+        for (i = 0;  i < 32;  i++) {
+                long r;
+                if ((i % 8) == 0)
+                        printk("\n" KERN_INFO "GPR%02d: ", i);
+                if (__get_user(r, &regs->gpr[i]))
+                        break;
+                printk("%08lX ", r);
+                if (i == 12 && !FULL_REGS(regs))
+                        break;
+        }
+        printk("\n");
+#ifdef CONFIG_KALLSYMS
+        /*
+         * Lookup NIP late so we have the best change of getting the
+         * above info out without failing
+         */
+        printk("NIP [%08lx] ", regs->nip);
+        print_symbol("%s\n", regs->nip);
+        printk("LR [%08lx] ", regs->link);
+        print_symbol("%s\n", regs->link);
+#endif
+        show_stack(current, (unsigned long *) regs->gpr[1]);
+}
+
+void exit_thread(void)
+{
+#ifndef CONFIG_SMP
+        if (last_task_used_math == current)
+                last_task_used_math = NULL;
+#ifdef CONFIG_ALTIVEC
+        if (last_task_used_altivec == current)
+                last_task_used_altivec = NULL;
+#endif /* CONFIG_ALTIVEC */
+#ifdef CONFIG_SPE
+        if (last_task_used_spe == current)
+                last_task_used_spe = NULL;
+#endif
+#endif /* CONFIG_SMP */
+}
+
+void flush_thread(void)
+{
+#ifndef CONFIG_SMP
+        if (last_task_used_math == current)
+                last_task_used_math = NULL;
+#ifdef CONFIG_ALTIVEC
+        if (last_task_used_altivec == current)
+                last_task_used_altivec = NULL;
+#endif /* CONFIG_ALTIVEC */
+#ifdef CONFIG_SPE
+        if (last_task_used_spe == current)
+                last_task_used_spe = NULL;
+#endif
+#endif /* CONFIG_SMP */
+
+#ifdef CONFIG_PPC64     /* for now */
+        if (current->thread.dabr) {
+                current->thread.dabr = 0;
+                set_dabr(0);
+        }
+#endif
+}
+
+void
+release_thread(struct task_struct *t)
+{
+}
+
+/*
+ * This gets called before we allocate a new thread and copy
+ * the current task into it.
+ */
+void prepare_to_copy(struct task_struct *tsk)
+{
+        flush_fp_to_thread(current);
+        flush_altivec_to_thread(current);
+        flush_spe_to_thread(current);
+}
+
+/*
+ * Copy a thread..
+ */
+int
+copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
+            unsigned long unused,
+            struct task_struct *p, struct pt_regs *regs)
+{
+        struct pt_regs *childregs, *kregs;
+        extern void ret_from_fork(void);
+        unsigned long sp = (unsigned long)p->thread_info + THREAD_SIZE;
+        unsigned long childframe;
+
+        CHECK_FULL_REGS(regs);
+        /* Copy registers */
+        sp -= sizeof(struct pt_regs);
+        childregs = (struct pt_regs *) sp;
+        *childregs = *regs;
+        if ((childregs->msr & MSR_PR) == 0) {
+                /* for kernel thread, set `current' and stackptr in new task */
+                childregs->gpr[1] = sp + sizeof(struct pt_regs);
+                childregs->gpr[2] = (unsigned long) p;
+                p->thread.regs = NULL;  /* no user register state */
+        } else {
+                childregs->gpr[1] = usp;
+                p->thread.regs = childregs;
+                if (clone_flags & CLONE_SETTLS)
+                        childregs->gpr[2] = childregs->gpr[6];
+        }
+        childregs->gpr[3] = 0;  /* Result from fork() */
+        sp -= STACK_FRAME_OVERHEAD;
+        childframe = sp;
+
+        /*
+         * The way this works is that at some point in the future
+         * some task will call _switch to switch to the new task.
+         * That will pop off the stack frame created below and start
+         * the new task running at ret_from_fork.  The new task will
+         * do some house keeping and then return from the fork or clone
+         * system call, using the stack frame created above.
+         */
+        sp -= sizeof(struct pt_regs);
+        kregs = (struct pt_regs *) sp;
+        sp -= STACK_FRAME_OVERHEAD;
+        p->thread.ksp = sp;
+        kregs->nip = (unsigned long)ret_from_fork;
+
+        p->thread.last_syscall = -1;
+
+        return 0;
+}
+
+/*
+ * Set up a thread for executing a new program
+ */
+void start_thread(struct pt_regs *regs, unsigned long nip, unsigned long sp)
+{
+        set_fs(USER_DS);
+        memset(regs->gpr, 0, sizeof(regs->gpr));
+        regs->ctr = 0;
+        regs->link = 0;
+        regs->xer = 0;
+        regs->ccr = 0;
+        regs->mq = 0;
+        regs->nip = nip;
+        regs->gpr[1] = sp;
+        regs->msr = MSR_USER;
+#ifndef CONFIG_SMP
+        if (last_task_used_math == current)
+                last_task_used_math = NULL;
+#ifdef CONFIG_ALTIVEC
+        if (last_task_used_altivec == current)
+                last_task_used_altivec = NULL;
+#endif
+#ifdef CONFIG_SPE
+        if (last_task_used_spe == current)
+                last_task_used_spe = NULL;
+#endif
+#endif /* CONFIG_SMP */
+        memset(current->thread.fpr, 0, sizeof(current->thread.fpr));
+        current->thread.fpscr = 0;
+#ifdef CONFIG_ALTIVEC
+        memset(current->thread.vr, 0, sizeof(current->thread.vr));
+        memset(&current->thread.vscr, 0, sizeof(current->thread.vscr));
+        current->thread.vrsave = 0;
+        current->thread.used_vr = 0;
+#endif /* CONFIG_ALTIVEC */
+#ifdef CONFIG_SPE
+        memset(current->thread.evr, 0, sizeof(current->thread.evr));
+        current->thread.acc = 0;
+        current->thread.spefscr = 0;
+        current->thread.used_spe = 0;
+#endif /* CONFIG_SPE */
+}
+
+#define PR_FP_ALL_EXCEPT (PR_FP_EXC_DIV | PR_FP_EXC_OVF | PR_FP_EXC_UND \
+                | PR_FP_EXC_RES | PR_FP_EXC_INV)
+
+int set_fpexc_mode(struct task_struct *tsk, unsigned int val)
+{
+        struct pt_regs *regs = tsk->thread.regs;
+
+        /* This is a bit hairy.  If we are an SPE enabled  processor
+         * (have embedded fp) we store the IEEE exception enable flags in
+         * fpexc_mode.  fpexc_mode is also used for setting FP exception
+         * mode (asyn, precise, disabled) for 'Classic' FP. */
+        if (val & PR_FP_EXC_SW_ENABLE) {
+#ifdef CONFIG_SPE
+                tsk->thread.fpexc_mode = val &
+                        (PR_FP_EXC_SW_ENABLE | PR_FP_ALL_EXCEPT);
+#else
+                return -EINVAL;
+#endif
+        } else {
+                /* on a CONFIG_SPE this does not hurt us.  The bits that
+                 * __pack_fe01 use do not overlap with bits used for
+                 * PR_FP_EXC_SW_ENABLE.  Additionally, the MSR[FE0,FE1] bits
+                 * on CONFIG_SPE implementations are reserved so writing to
+                 * them does not change anything */
+                if (val > PR_FP_EXC_PRECISE)
+                        return -EINVAL;
+                tsk->thread.fpexc_mode = __pack_fe01(val);
+                if (regs != NULL && (regs->msr & MSR_FP) != 0)
+                        regs->msr = (regs->msr & ~(MSR_FE0|MSR_FE1))
+                                | tsk->thread.fpexc_mode;
+        }
+        return 0;
+}
+
+int get_fpexc_mode(struct task_struct *tsk, unsigned long adr)
+{
+        unsigned int val;
+
+        if (tsk->thread.fpexc_mode & PR_FP_EXC_SW_ENABLE)
+#ifdef CONFIG_SPE
+                val = tsk->thread.fpexc_mode;
+#else
+                return -EINVAL;
+#endif
+        else
+                val = __unpack_fe01(tsk->thread.fpexc_mode);
+        return put_user(val, (unsigned int __user *) adr);
+}
+
+int sys_clone(unsigned long clone_flags, unsigned long usp,
+              int __user *parent_tidp, void __user *child_threadptr,
+              int __user *child_tidp, int p6,
+              struct pt_regs *regs)
+{
+        CHECK_FULL_REGS(regs);
+        if (usp == 0)
+                usp = regs->gpr[1];     /* stack pointer for child */
+        return do_fork(clone_flags, usp, regs, 0, parent_tidp, child_tidp);
+}
+
+int sys_fork(unsigned long p1, unsigned long p2, unsigned long p3,
+             unsigned long p4, unsigned long p5, unsigned long p6,
+             struct pt_regs *regs)
+{
+        CHECK_FULL_REGS(regs);
+        return do_fork(SIGCHLD, regs->gpr[1], regs, 0, NULL, NULL);
+}
+
+int sys_vfork(unsigned long p1, unsigned long p2, unsigned long p3,
+              unsigned long p4, unsigned long p5, unsigned long p6,
+              struct pt_regs *regs)
+{
+        CHECK_FULL_REGS(regs);
+        return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs->gpr[1],
+                        regs, 0, NULL, NULL);
+}
+
+int sys_execve(unsigned long a0, unsigned long a1, unsigned long a2,
+               unsigned long a3, unsigned long a4, unsigned long a5,
+               struct pt_regs *regs)
+{
+        int error;
+        char * filename;
+
+        filename = getname((char __user *) a0);
+        error = PTR_ERR(filename);
+        if (IS_ERR(filename))
+                goto out;
+        flush_fp_to_thread(current);
+        flush_altivec_to_thread(current);
+        flush_spe_to_thread(current);
+        if (error == 0) {
+                task_lock(current);
+                current->ptrace &= ~PT_DTRACE;
+                task_unlock(current);
+        }
+        putname(filename);
+out:
+        return error;
+}
+
+static int validate_sp(unsigned long sp, struct task_struct *p,
+                       unsigned long nbytes)
+{
+        unsigned long stack_page = (unsigned long)p->thread_info;
+
+        if (sp >= stack_page + sizeof(struct thread_struct)
+            && sp <= stack_page + THREAD_SIZE - nbytes)
+                return 1;
+
+#ifdef CONFIG_IRQSTACKS
+        stack_page = (unsigned long) hardirq_ctx[task_cpu(p)];
+        if (sp >= stack_page + sizeof(struct thread_struct)
+            && sp <= stack_page + THREAD_SIZE - nbytes)
+                return 1;
+
+        stack_page = (unsigned long) softirq_ctx[task_cpu(p)];
+        if (sp >= stack_page + sizeof(struct thread_struct)
+            && sp <= stack_page + THREAD_SIZE - nbytes)
+                return 1;
+#endif
+
+        return 0;
+}
+
+void dump_stack(void)
+{
+        show_stack(current, NULL);
+}
+
+EXPORT_SYMBOL(dump_stack);
+
+void show_stack(struct task_struct *tsk, unsigned long *stack)
+{
+        unsigned long sp, stack_top, prev_sp, ret;
+        int count = 0;
+        unsigned long next_exc = 0;
+        struct pt_regs *regs;
+        extern char ret_from_except, ret_from_except_full, ret_from_syscall;
+
+        sp = (unsigned long) stack;
+        if (tsk == NULL)
+                tsk = current;
+        if (sp == 0) {
+                if (tsk == current)
+                        asm("mr %0,1" : "=r" (sp));
+                else
+                        sp = tsk->thread.ksp;
+        }
+
+        prev_sp = (unsigned long) (tsk->thread_info + 1);
+        stack_top = (unsigned long) tsk->thread_info + THREAD_SIZE;
+        while (count < 16 && sp > prev_sp && sp < stack_top && (sp & 3) == 0) {
+                if (count == 0) {
+                        printk("Call trace:");
+#ifdef CONFIG_KALLSYMS
+                        printk("\n");
+#endif
+                } else {
+                        if (next_exc) {
+                                ret = next_exc;
+                                next_exc = 0;
+                        } else
+                                ret = *(unsigned long *)(sp + 4);
+                        printk(" [%08lx] ", ret);
+#ifdef CONFIG_KALLSYMS
+                        print_symbol("%s", ret);
+                        printk("\n");
+#endif
+                        if (ret == (unsigned long) &ret_from_except
+                            || ret == (unsigned long) &ret_from_except_full
+                            || ret == (unsigned long) &ret_from_syscall) {
+                                /* sp + 16 points to an exception frame */
+                                regs = (struct pt_regs *) (sp + 16);
+                                if (sp + 16 + sizeof(*regs) <= stack_top)
+                                        next_exc = regs->nip;
+                        }
+                }
+                ++count;
+                sp = *(unsigned long *)sp;
+        }
+#ifndef CONFIG_KALLSYMS
+        if (count > 0)
+                printk("\n");
+#endif
+}
+
+unsigned long get_wchan(struct task_struct *p)
+{
+        unsigned long ip, sp;
+        int count = 0;
+
+        if (!p || p == current || p->state == TASK_RUNNING)
+                return 0;
+
+        sp = p->thread.ksp;
+        if (!validate_sp(sp, p, 16))
+                return 0;
+
+        do {
+                sp = *(unsigned long *)sp;
+                if (!validate_sp(sp, p, 16))
+                        return 0;
+                if (count > 0) {
+                        ip = *(unsigned long *)(sp + 4);
+                        if (!in_sched_functions(ip))
+                                return ip;
+                }
+        } while (count++ < 16);
+        return 0;
+}
+EXPORT_SYMBOL(get_wchan);