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![Chris Metcalf](/assets/img/avatar_default.png)
Fix a long-standing bug in the stack backtracer where we would print garbage to the console instead of kernel function names, if the kernel wasn't built with symbol support (e.g. mboot). Make sure to tag every line of userspace backtrace output if we actually have the mmap_sem, since that way if there's no tag, we know that it's because we couldn't trylock the semaphore. Stop doing a TLB flush and examining page tables during backtrace. Instead, just trust that __copy_from_user_inatomic() will properly fault and return a failure, which it should do in all cases. Fix a latent bug where the backtracer would directly examine a signal context in user space, rather than copying it safely to kernel memory first. This meant that a race with another thread could potentially have caused a kernel panic. Guard against unaligned sp when trying to restart backtrace at an interrupt or signal handler point in the kernel backtracer. Report kernel symbolic information for the call instruction rather than for the following instruction. We still report the actual numeric address corresponding to the instruction after the call, for the sake of consistency with the normal expectations for stack backtracers. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
491 lines
14 KiB
C
491 lines
14 KiB
C
/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*/
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/kprobes.h>
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#include <linux/module.h>
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#include <linux/pfn.h>
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#include <linux/kallsyms.h>
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#include <linux/stacktrace.h>
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#include <linux/uaccess.h>
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#include <linux/mmzone.h>
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#include <linux/dcache.h>
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#include <linux/fs.h>
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#include <asm/backtrace.h>
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#include <asm/page.h>
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#include <asm/ucontext.h>
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#include <asm/switch_to.h>
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#include <asm/sigframe.h>
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#include <asm/stack.h>
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#include <arch/abi.h>
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#include <arch/interrupts.h>
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#define KBT_ONGOING 0 /* Backtrace still ongoing */
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#define KBT_DONE 1 /* Backtrace cleanly completed */
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#define KBT_RUNNING 2 /* Can't run backtrace on a running task */
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#define KBT_LOOP 3 /* Backtrace entered a loop */
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/* Is address on the specified kernel stack? */
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static int in_kernel_stack(struct KBacktraceIterator *kbt, unsigned long sp)
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{
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ulong kstack_base = (ulong) kbt->task->stack;
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if (kstack_base == 0) /* corrupt task pointer; just follow stack... */
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return sp >= PAGE_OFFSET && sp < (unsigned long)high_memory;
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return sp >= kstack_base && sp < kstack_base + THREAD_SIZE;
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}
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/* Callback for backtracer; basically a glorified memcpy */
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static bool read_memory_func(void *result, unsigned long address,
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unsigned int size, void *vkbt)
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{
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int retval;
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struct KBacktraceIterator *kbt = (struct KBacktraceIterator *)vkbt;
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if (address == 0)
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return 0;
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if (__kernel_text_address(address)) {
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/* OK to read kernel code. */
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} else if (address >= PAGE_OFFSET) {
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/* We only tolerate kernel-space reads of this task's stack */
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if (!in_kernel_stack(kbt, address))
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return 0;
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} else if (!kbt->is_current) {
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return 0; /* can't read from other user address spaces */
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}
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pagefault_disable();
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retval = __copy_from_user_inatomic(result,
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(void __user __force *)address,
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size);
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pagefault_enable();
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return (retval == 0);
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}
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/* Return a pt_regs pointer for a valid fault handler frame */
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static struct pt_regs *valid_fault_handler(struct KBacktraceIterator* kbt)
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{
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const char *fault = NULL; /* happy compiler */
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char fault_buf[64];
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unsigned long sp = kbt->it.sp;
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struct pt_regs *p;
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if (sp % sizeof(long) != 0)
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return NULL;
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if (!in_kernel_stack(kbt, sp))
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return NULL;
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if (!in_kernel_stack(kbt, sp + C_ABI_SAVE_AREA_SIZE + PTREGS_SIZE-1))
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return NULL;
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p = (struct pt_regs *)(sp + C_ABI_SAVE_AREA_SIZE);
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if (p->faultnum == INT_SWINT_1 || p->faultnum == INT_SWINT_1_SIGRETURN)
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fault = "syscall";
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else {
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if (kbt->verbose) { /* else we aren't going to use it */
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snprintf(fault_buf, sizeof(fault_buf),
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"interrupt %ld", p->faultnum);
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fault = fault_buf;
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}
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}
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if (EX1_PL(p->ex1) == KERNEL_PL &&
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__kernel_text_address(p->pc) &&
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in_kernel_stack(kbt, p->sp) &&
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p->sp >= sp) {
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if (kbt->verbose)
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pr_err(" <%s while in kernel mode>\n", fault);
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} else if (EX1_PL(p->ex1) == USER_PL &&
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p->pc < PAGE_OFFSET &&
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p->sp < PAGE_OFFSET) {
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if (kbt->verbose)
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pr_err(" <%s while in user mode>\n", fault);
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} else if (kbt->verbose) {
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pr_err(" (odd fault: pc %#lx, sp %#lx, ex1 %#lx?)\n",
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p->pc, p->sp, p->ex1);
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p = NULL;
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}
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if (!kbt->profile || (INT_MASK(p->faultnum) & QUEUED_INTERRUPTS) == 0)
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return p;
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return NULL;
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}
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/* Is the pc pointing to a sigreturn trampoline? */
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static int is_sigreturn(unsigned long pc)
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{
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return (pc == VDSO_BASE);
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}
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/* Return a pt_regs pointer for a valid signal handler frame */
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static struct pt_regs *valid_sigframe(struct KBacktraceIterator* kbt,
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struct rt_sigframe* kframe)
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{
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BacktraceIterator *b = &kbt->it;
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if (b->pc == VDSO_BASE && b->sp < PAGE_OFFSET &&
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b->sp % sizeof(long) == 0) {
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int retval;
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pagefault_disable();
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retval = __copy_from_user_inatomic(
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kframe, (void __user __force *)b->sp,
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sizeof(*kframe));
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pagefault_enable();
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if (retval != 0 ||
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(unsigned int)(kframe->info.si_signo) >= _NSIG)
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return NULL;
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if (kbt->verbose) {
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pr_err(" <received signal %d>\n",
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kframe->info.si_signo);
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}
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return (struct pt_regs *)&kframe->uc.uc_mcontext;
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}
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return NULL;
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}
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static int KBacktraceIterator_is_sigreturn(struct KBacktraceIterator *kbt)
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{
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return is_sigreturn(kbt->it.pc);
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}
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static int KBacktraceIterator_restart(struct KBacktraceIterator *kbt)
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{
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struct pt_regs *p;
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struct rt_sigframe kframe;
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p = valid_fault_handler(kbt);
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if (p == NULL)
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p = valid_sigframe(kbt, &kframe);
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if (p == NULL)
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return 0;
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backtrace_init(&kbt->it, read_memory_func, kbt,
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p->pc, p->lr, p->sp, p->regs[52]);
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kbt->new_context = 1;
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return 1;
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}
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/* Find a frame that isn't a sigreturn, if there is one. */
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static int KBacktraceIterator_next_item_inclusive(
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struct KBacktraceIterator *kbt)
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{
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for (;;) {
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do {
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if (!KBacktraceIterator_is_sigreturn(kbt))
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return KBT_ONGOING;
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} while (backtrace_next(&kbt->it));
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if (!KBacktraceIterator_restart(kbt))
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return KBT_DONE;
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}
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}
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/*
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* If the current sp is on a page different than what we recorded
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* as the top-of-kernel-stack last time we context switched, we have
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* probably blown the stack, and nothing is going to work out well.
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* If we can at least get out a warning, that may help the debug,
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* though we probably won't be able to backtrace into the code that
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* actually did the recursive damage.
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*/
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static void validate_stack(struct pt_regs *regs)
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{
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int cpu = smp_processor_id();
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unsigned long ksp0 = get_current_ksp0();
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unsigned long ksp0_base = ksp0 - THREAD_SIZE;
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unsigned long sp = stack_pointer;
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if (EX1_PL(regs->ex1) == KERNEL_PL && regs->sp >= ksp0) {
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pr_err("WARNING: cpu %d: kernel stack page %#lx underrun!\n"
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" sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
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cpu, ksp0_base, sp, regs->sp, regs->pc, regs->lr);
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}
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else if (sp < ksp0_base + sizeof(struct thread_info)) {
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pr_err("WARNING: cpu %d: kernel stack page %#lx overrun!\n"
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" sp %#lx (%#lx in caller), caller pc %#lx, lr %#lx\n",
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cpu, ksp0_base, sp, regs->sp, regs->pc, regs->lr);
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}
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}
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void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
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struct task_struct *t, struct pt_regs *regs)
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{
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unsigned long pc, lr, sp, r52;
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int is_current;
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/*
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* Set up callback information. We grab the kernel stack base
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* so we will allow reads of that address range.
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*/
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is_current = (t == NULL || t == current);
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kbt->is_current = is_current;
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if (is_current)
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t = validate_current();
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kbt->task = t;
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kbt->verbose = 0; /* override in caller if desired */
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kbt->profile = 0; /* override in caller if desired */
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kbt->end = KBT_ONGOING;
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kbt->new_context = 1;
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if (is_current)
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validate_stack(regs);
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if (regs == NULL) {
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if (is_current || t->state == TASK_RUNNING) {
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/* Can't do this; we need registers */
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kbt->end = KBT_RUNNING;
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return;
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}
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pc = get_switch_to_pc();
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lr = t->thread.pc;
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sp = t->thread.ksp;
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r52 = 0;
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} else {
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pc = regs->pc;
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lr = regs->lr;
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sp = regs->sp;
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r52 = regs->regs[52];
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}
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backtrace_init(&kbt->it, read_memory_func, kbt, pc, lr, sp, r52);
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kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
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}
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EXPORT_SYMBOL(KBacktraceIterator_init);
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int KBacktraceIterator_end(struct KBacktraceIterator *kbt)
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{
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return kbt->end != KBT_ONGOING;
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}
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EXPORT_SYMBOL(KBacktraceIterator_end);
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void KBacktraceIterator_next(struct KBacktraceIterator *kbt)
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{
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unsigned long old_pc = kbt->it.pc, old_sp = kbt->it.sp;
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kbt->new_context = 0;
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if (!backtrace_next(&kbt->it) && !KBacktraceIterator_restart(kbt)) {
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kbt->end = KBT_DONE;
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return;
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}
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kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
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if (old_pc == kbt->it.pc && old_sp == kbt->it.sp) {
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/* Trapped in a loop; give up. */
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kbt->end = KBT_LOOP;
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}
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}
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EXPORT_SYMBOL(KBacktraceIterator_next);
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static void describe_addr(struct KBacktraceIterator *kbt,
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unsigned long address,
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int have_mmap_sem, char *buf, size_t bufsize)
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{
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struct vm_area_struct *vma;
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size_t namelen, remaining;
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unsigned long size, offset, adjust;
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char *p, *modname;
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const char *name;
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int rc;
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/*
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* Look one byte back for every caller frame (i.e. those that
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* aren't a new context) so we look up symbol data for the
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* call itself, not the following instruction, which may be on
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* a different line (or in a different function).
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*/
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adjust = !kbt->new_context;
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address -= adjust;
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if (address >= PAGE_OFFSET) {
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/* Handle kernel symbols. */
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BUG_ON(bufsize < KSYM_NAME_LEN);
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name = kallsyms_lookup(address, &size, &offset,
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&modname, buf);
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if (name == NULL) {
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buf[0] = '\0';
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return;
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}
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namelen = strlen(buf);
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remaining = (bufsize - 1) - namelen;
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p = buf + namelen;
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rc = snprintf(p, remaining, "+%#lx/%#lx ",
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offset + adjust, size);
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if (modname && rc < remaining)
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snprintf(p + rc, remaining - rc, "[%s] ", modname);
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buf[bufsize-1] = '\0';
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return;
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}
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/* If we don't have the mmap_sem, we can't show any more info. */
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buf[0] = '\0';
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if (!have_mmap_sem)
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return;
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/* Find vma info. */
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vma = find_vma(kbt->task->mm, address);
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if (vma == NULL || address < vma->vm_start) {
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snprintf(buf, bufsize, "[unmapped address] ");
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return;
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}
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if (vma->vm_file) {
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char *s;
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p = d_path(&vma->vm_file->f_path, buf, bufsize);
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if (IS_ERR(p))
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p = "?";
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s = strrchr(p, '/');
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if (s)
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p = s+1;
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} else {
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p = "anon";
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}
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/* Generate a string description of the vma info. */
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namelen = strlen(p);
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remaining = (bufsize - 1) - namelen;
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memmove(buf, p, namelen);
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snprintf(buf + namelen, remaining, "[%lx+%lx] ",
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vma->vm_start, vma->vm_end - vma->vm_start);
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}
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/*
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* This method wraps the backtracer's more generic support.
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* It is only invoked from the architecture-specific code; show_stack()
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* and dump_stack() (in entry.S) are architecture-independent entry points.
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*/
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void tile_show_stack(struct KBacktraceIterator *kbt, int headers)
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{
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int i;
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int have_mmap_sem = 0;
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if (headers) {
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/*
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* Add a blank line since if we are called from panic(),
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* then bust_spinlocks() spit out a space in front of us
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* and it will mess up our KERN_ERR.
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*/
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pr_err("\n");
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pr_err("Starting stack dump of tid %d, pid %d (%s)"
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" on cpu %d at cycle %lld\n",
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kbt->task->pid, kbt->task->tgid, kbt->task->comm,
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smp_processor_id(), get_cycles());
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}
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kbt->verbose = 1;
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i = 0;
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for (; !KBacktraceIterator_end(kbt); KBacktraceIterator_next(kbt)) {
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char namebuf[KSYM_NAME_LEN+100];
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unsigned long address = kbt->it.pc;
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/* Try to acquire the mmap_sem as we pass into userspace. */
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if (address < PAGE_OFFSET && !have_mmap_sem && kbt->task->mm)
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have_mmap_sem =
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down_read_trylock(&kbt->task->mm->mmap_sem);
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describe_addr(kbt, address, have_mmap_sem,
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namebuf, sizeof(namebuf));
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pr_err(" frame %d: 0x%lx %s(sp 0x%lx)\n",
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i++, address, namebuf, (unsigned long)(kbt->it.sp));
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if (i >= 100) {
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pr_err("Stack dump truncated"
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" (%d frames)\n", i);
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break;
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}
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}
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if (kbt->end == KBT_LOOP)
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pr_err("Stack dump stopped; next frame identical to this one\n");
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if (headers)
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pr_err("Stack dump complete\n");
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if (have_mmap_sem)
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up_read(&kbt->task->mm->mmap_sem);
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}
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EXPORT_SYMBOL(tile_show_stack);
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/* This is called from show_regs() and _dump_stack() */
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void dump_stack_regs(struct pt_regs *regs)
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{
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struct KBacktraceIterator kbt;
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KBacktraceIterator_init(&kbt, NULL, regs);
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tile_show_stack(&kbt, 1);
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}
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EXPORT_SYMBOL(dump_stack_regs);
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static struct pt_regs *regs_to_pt_regs(struct pt_regs *regs,
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ulong pc, ulong lr, ulong sp, ulong r52)
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{
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memset(regs, 0, sizeof(struct pt_regs));
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regs->pc = pc;
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regs->lr = lr;
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regs->sp = sp;
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regs->regs[52] = r52;
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return regs;
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}
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/* This is called from dump_stack() and just converts to pt_regs */
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void _dump_stack(int dummy, ulong pc, ulong lr, ulong sp, ulong r52)
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{
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struct pt_regs regs;
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dump_stack_regs(regs_to_pt_regs(®s, pc, lr, sp, r52));
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}
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/* This is called from KBacktraceIterator_init_current() */
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void _KBacktraceIterator_init_current(struct KBacktraceIterator *kbt, ulong pc,
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ulong lr, ulong sp, ulong r52)
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{
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struct pt_regs regs;
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KBacktraceIterator_init(kbt, NULL,
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regs_to_pt_regs(®s, pc, lr, sp, r52));
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}
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/* This is called only from kernel/sched.c, with esp == NULL */
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void show_stack(struct task_struct *task, unsigned long *esp)
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{
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struct KBacktraceIterator kbt;
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if (task == NULL || task == current)
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KBacktraceIterator_init_current(&kbt);
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else
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KBacktraceIterator_init(&kbt, task, NULL);
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tile_show_stack(&kbt, 0);
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}
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#ifdef CONFIG_STACKTRACE
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/* Support generic Linux stack API too */
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void save_stack_trace_tsk(struct task_struct *task, struct stack_trace *trace)
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{
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struct KBacktraceIterator kbt;
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int skip = trace->skip;
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int i = 0;
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if (task == NULL || task == current)
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KBacktraceIterator_init_current(&kbt);
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else
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KBacktraceIterator_init(&kbt, task, NULL);
|
|
for (; !KBacktraceIterator_end(&kbt); KBacktraceIterator_next(&kbt)) {
|
|
if (skip) {
|
|
--skip;
|
|
continue;
|
|
}
|
|
if (i >= trace->max_entries || kbt.it.pc < PAGE_OFFSET)
|
|
break;
|
|
trace->entries[i++] = kbt.it.pc;
|
|
}
|
|
trace->nr_entries = i;
|
|
}
|
|
EXPORT_SYMBOL(save_stack_trace_tsk);
|
|
|
|
void save_stack_trace(struct stack_trace *trace)
|
|
{
|
|
save_stack_trace_tsk(NULL, trace);
|
|
}
|
|
|
|
#endif
|
|
|
|
/* In entry.S */
|
|
EXPORT_SYMBOL(KBacktraceIterator_init_current);
|