uretprobes: Reserve the first slot in xol_vma for trampoline
Allocate trampoline page, as the very first one in uprobed task xol area, and fill it with breakpoint opcode. Also introduce get_trampoline_vaddr() helper, to wrap the trampoline address extraction from area->vaddr. That removes confusion and eases the debug experience in case ->vaddr notion will be changed. Signed-off-by: Anton Arapov <anton@redhat.com> Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
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@ -1132,6 +1132,7 @@ static struct xol_area *get_xol_area(void)
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{
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struct mm_struct *mm = current->mm;
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struct xol_area *area;
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uprobe_opcode_t insn = UPROBE_SWBP_INSN;
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area = mm->uprobes_state.xol_area;
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if (area)
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@ -1149,7 +1150,12 @@ static struct xol_area *get_xol_area(void)
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if (!area->page)
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goto free_bitmap;
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/* allocate first slot of task's xol_area for the return probes */
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set_bit(0, area->bitmap);
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copy_to_page(area->page, 0, &insn, UPROBE_SWBP_INSN_SIZE);
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atomic_set(&area->slot_count, 1);
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init_waitqueue_head(&area->wq);
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if (!xol_add_vma(area))
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return area;
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@ -1346,6 +1352,25 @@ static struct uprobe_task *get_utask(void)
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return current->utask;
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}
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/*
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* Current area->vaddr notion assume the trampoline address is always
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* equal area->vaddr.
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*
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* Returns -1 in case the xol_area is not allocated.
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*/
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static unsigned long get_trampoline_vaddr(void)
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{
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struct xol_area *area;
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unsigned long trampoline_vaddr = -1;
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area = current->mm->uprobes_state.xol_area;
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smp_read_barrier_depends();
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if (area)
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trampoline_vaddr = area->vaddr;
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return trampoline_vaddr;
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}
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/* Prepare to single-step probed instruction out of line. */
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static int
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pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
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