linux-kernel - Re: [PATCH] LoongArch: uprobes: make UPROBE_SWBP_INSN/UPROBE_XOLBP

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Date: Thu, 27 Jun 2024 09:51:35 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, Jiri Olsa <jolsa@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Nathan Chancellor <nathan@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev
Subject: Re: [PATCH] LoongArch: uprobes: make UPROBE_SWBP_INSN/UPROBE_XOLBP_INSN
 constant

On Thu, Jun 27, 2024 at 9:04 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> LoongArch defines UPROBE_SWBP_INSN as a function call and this breaks
> arch_uprobe_trampoline() which uses it to initialize a static variable.
>
> Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Closes: https://lore.kernel.org/all/20240614174822.GA1185149@thelio-3990X/
> Suggested-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  arch/loongarch/include/asm/uprobes.h | 6 ++++--
>  arch/loongarch/kernel/uprobes.c      | 8 ++++++++
>  2 files changed, 12 insertions(+), 2 deletions(-)
>

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>


> diff --git a/arch/loongarch/include/asm/uprobes.h b/arch/loongarch/include/asm/uprobes.h
> index c8f59983f702..18221eb9a8b0 100644
> --- a/arch/loongarch/include/asm/uprobes.h
> +++ b/arch/loongarch/include/asm/uprobes.h
> @@ -6,13 +6,15 @@
>
>  typedef u32 uprobe_opcode_t;
>
> +#define __emit_break(imm)      (uprobe_opcode_t)((imm) | (break_op << 15))
> +
>  #define MAX_UINSN_BYTES                8
>  #define UPROBE_XOL_SLOT_BYTES  MAX_UINSN_BYTES
>
> -#define UPROBE_SWBP_INSN       larch_insn_gen_break(BRK_UPROBE_BP)
> +#define UPROBE_SWBP_INSN       __emit_break(BRK_UPROBE_BP)
>  #define UPROBE_SWBP_INSN_SIZE  LOONGARCH_INSN_SIZE
>
> -#define UPROBE_XOLBP_INSN      larch_insn_gen_break(BRK_UPROBE_XOLBP)
> +#define UPROBE_XOLBP_INSN      __emit_break(BRK_UPROBE_XOLBP)
>

this looks correct (but based on pure code inspection)

>  struct arch_uprobe {
>         unsigned long   resume_era;
> diff --git a/arch/loongarch/kernel/uprobes.c b/arch/loongarch/kernel/uprobes.c
> index 87abc7137b73..90462d94c28f 100644
> --- a/arch/loongarch/kernel/uprobes.c
> +++ b/arch/loongarch/kernel/uprobes.c
> @@ -7,6 +7,14 @@
>
>  #define UPROBE_TRAP_NR UINT_MAX
>
> +static __init int check_emit_break(void)
> +{
> +       BUG_ON(UPROBE_SWBP_INSN  != larch_insn_gen_break(BRK_UPROBE_BP));
> +       BUG_ON(UPROBE_XOLBP_INSN != larch_insn_gen_break(BRK_UPROBE_XOLBP));
> +       return 0;
> +}
> +arch_initcall(check_emit_break);
> +

I wouldn't even bother with this, but whatever.

>  int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
>                              struct mm_struct *mm, unsigned long addr)
>  {
> --
> 2.25.1.362.g51ebf55
>
>