Re: [PATCH] LoongArch: make the users of larch_insn_gen_break() constant

Huacai Chen
2024-06-30T01:43:43Z

Hi, Oleg,

On Sat, Jun 29, 2024 at 11:05 PM Oleg Nesterov <oleg@redhat.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@kernel.org>
> Closes: https://lore.kernel.org/all/20240614174822.GA1185149@thelio-3990X/
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Oleg Nesterov <oleg@redhat.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
>
>