Re: [PATCHv8 bpf-next 3/9] uprobe: Add uretprobe syscall to speed up return probe

[Nathan Chancellor <nathan@kernel.org>]

Hi Jiri,

On Tue, Jun 11, 2024 at 01:21:52PM +0200, Jiri Olsa wrote:
> Adding uretprobe syscall instead of trap to speed up return probe.
...
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 2c83ba776fc7..2816e65729ac 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1474,11 +1474,20 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
>  	return ret;
>  }
>  
> +void * __weak arch_uprobe_trampoline(unsigned long *psize)
> +{
> +	static uprobe_opcode_t insn = UPROBE_SWBP_INSN;

This change as commit ff474a78cef5 ("uprobe: Add uretprobe syscall to
speed up return probe") in -next causes the following build error for
ARCH=loongarch allmodconfig:

  In file included from include/linux/uprobes.h:49,
                   from include/linux/mm_types.h:16,
                   from include/linux/mmzone.h:22,
                   from include/linux/gfp.h:7,
                   from include/linux/xarray.h:16,
                   from include/linux/list_lru.h:14,
                   from include/linux/fs.h:13,
                   from include/linux/highmem.h:5,
                   from kernel/events/uprobes.c:13:
  kernel/events/uprobes.c: In function 'arch_uprobe_trampoline':
  arch/loongarch/include/asm/uprobes.h:12:33: error: initializer element is not constant
     12 | #define UPROBE_SWBP_INSN        larch_insn_gen_break(BRK_UPROBE_BP)
        |                                 ^~~~~~~~~~~~~~~~~~~~
  kernel/events/uprobes.c:1479:39: note: in expansion of macro 'UPROBE_SWBP_INSN'
   1479 |         static uprobe_opcode_t insn = UPROBE_SWBP_INSN;
        |                                       ^~~~~~~~~~~~~~~~

> +	*psize = UPROBE_SWBP_INSN_SIZE;
> +	return &insn;
> +}
> +
>  static struct xol_area *__create_xol_area(unsigned long vaddr)
>  {
>  	struct mm_struct *mm = current->mm;
> -	uprobe_opcode_t insn = UPROBE_SWBP_INSN;
> +	unsigned long insns_size;
>  	struct xol_area *area;
> +	void *insns;
>  
>  	area = kmalloc(sizeof(*area), GFP_KERNEL);
>  	if (unlikely(!area))
> @@ -1502,7 +1511,8 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
>  	/* Reserve the 1st slot for get_trampoline_vaddr() */
>  	set_bit(0, area->bitmap);
>  	atomic_set(&area->slot_count, 1);
> -	arch_uprobe_copy_ixol(area->pages[0], 0, &insn, UPROBE_SWBP_INSN_SIZE);
> +	insns = arch_uprobe_trampoline(&insns_size);
> +	arch_uprobe_copy_ixol(area->pages[0], 0, insns, insns_size);
>  
>  	if (!xol_add_vma(mm, area))
>  		return area;
> @@ -1827,7 +1837,7 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
>   *
>   * Returns -1 in case the xol_area is not allocated.
>   */
> -static unsigned long get_trampoline_vaddr(void)
> +unsigned long uprobe_get_trampoline_vaddr(void)
>  {
>  	struct xol_area *area;
>  	unsigned long trampoline_vaddr = -1;
> @@ -1878,7 +1888,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
>  	if (!ri)
>  		return;
>  
> -	trampoline_vaddr = get_trampoline_vaddr();
> +	trampoline_vaddr = uprobe_get_trampoline_vaddr();
>  	orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
>  	if (orig_ret_vaddr == -1)
>  		goto fail;
> @@ -2123,7 +2133,7 @@ static struct return_instance *find_next_ret_chain(struct return_instance *ri)
>  	return ri;
>  }
>  
> -static void handle_trampoline(struct pt_regs *regs)
> +void uprobe_handle_trampoline(struct pt_regs *regs)
>  {
>  	struct uprobe_task *utask;
>  	struct return_instance *ri, *next;
> @@ -2187,8 +2197,8 @@ static void handle_swbp(struct pt_regs *regs)
>  	int is_swbp;
>  
>  	bp_vaddr = uprobe_get_swbp_addr(regs);
> -	if (bp_vaddr == get_trampoline_vaddr())
> -		return handle_trampoline(regs);
> +	if (bp_vaddr == uprobe_get_trampoline_vaddr())
> +		return uprobe_handle_trampoline(regs);
>  
>  	uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
>  	if (!uprobe) {
> -- 
> 2.45.1
> 

Cheers,
Nathan