linux-kernel - Re: [PATCH] LoongArch: make the users of larch_insn_gen

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Date: Sun, 30 Jun 2024 09:43:30 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, andrii.nakryiko@...il.com, andrii@...nel.org, 
	bpf@...r.kernel.org, jolsa@...nel.org, kernel@...0n.name, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	loongarch@...ts.linux.dev, mhiramat@...nel.org, nathan@...nel.org, 
	rostedt@...dmis.org
Subject: Re: [PATCH] LoongArch: make the users of larch_insn_gen_break() constant

Hi, Oleg,

On Sat, Jun 29, 2024 at 11:05 PM 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.
>
> Add the new "__builtin_constant_p" helper, __emit_break(), and redefine
> the current users of larch_insn_gen_break() to use it.
>
> The patch adds check_emit_break() into kprobes.c and uprobes.c to test
> this change. They can be removed if LoongArch boots at least once, but
> otoh these 2 __init functions will be discarded by free_initmem().
>
> 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/inst.h    |  3 +++
>  arch/loongarch/include/asm/uprobes.h |  4 ++--
>  arch/loongarch/kernel/kprobes.c      | 12 ++++++++++--
>  arch/loongarch/kernel/uprobes.c      |  8 ++++++++
>  4 files changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index c3993fd88aba..944482063f14 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -532,6 +532,9 @@ static inline void emit_##NAME(union loongarch_instruction *insn,   \
>
>  DEF_EMIT_REG0I15_FORMAT(break, break_op)
>
> +/* like emit_break(imm) but returns a constant expression */
> +#define __emit_break(imm)      ((u32)((imm) | (break_op << 15)))
> +
>  #define DEF_EMIT_REG0I26_FORMAT(NAME, OP)                              \
>  static inline void emit_##NAME(union loongarch_instruction *insn,      \
>                                int offset)                              \
> diff --git a/arch/loongarch/include/asm/uprobes.h b/arch/loongarch/include/asm/uprobes.h
> index c8f59983f702..99a0d198927f 100644
> --- a/arch/loongarch/include/asm/uprobes.h
> +++ b/arch/loongarch/include/asm/uprobes.h
> @@ -9,10 +9,10 @@ typedef u32 uprobe_opcode_t;
>  #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)
>
>  struct arch_uprobe {
>         unsigned long   resume_era;
> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
> index 17b040bd6067..78cfaac52748 100644
> --- a/arch/loongarch/kernel/kprobes.c
> +++ b/arch/loongarch/kernel/kprobes.c
> @@ -4,8 +4,16 @@
>  #include <linux/preempt.h>
>  #include <asm/break.h>
>
> -#define KPROBE_BP_INSN         larch_insn_gen_break(BRK_KPROBE_BP)
> -#define KPROBE_SSTEPBP_INSN    larch_insn_gen_break(BRK_KPROBE_SSTEPBP)
> +#define KPROBE_BP_INSN         __emit_break(BRK_KPROBE_BP)
> +#define KPROBE_SSTEPBP_INSN    __emit_break(BRK_KPROBE_SSTEPBP)
> +
> +static __init int check_emit_break(void)
> +{
> +       BUG_ON(KPROBE_BP_INSN      != larch_insn_gen_break(BRK_KPROBE_BP));
> +       BUG_ON(KPROBE_SSTEPBP_INSN != larch_insn_gen_break(BRK_KPROBE_SSTEPBP));
> +       return 0;
> +}
> +arch_initcall(check_emit_break);
>
>  DEFINE_PER_CPU(struct kprobe *, current_kprobe);
>  DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> 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);
Do you mind if I remove the runtime checking after Tiezhu tests the correctness?

Huacai

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