Re: [PATCH] ARM: kprobes: Make __kretprobe_trampoline as a pure asm function

[Masami Hiramatsu <mhiramat@kernel.org>]

Hi,

I found a better solution for this issue from Ard :-)

https://lore.kernel.org/all/20220203082204.1176734-6-ardb@kernel.org/T/#u

I should use mov_l instead of ldr for loading the symbol address.

Thank you,

On Tue, 15 Mar 2022 18:52:16 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Make __kretprobe_trampoline() as a pure asm function same as the x86
> code does. Anyway, it is safe to define the symbol in the asm code
> instead of accessing a C symbol from the inline asm.
> 
> Without this fix, building arm kernel with GCC-11 may cause below
> error.
> 
>    /tmp/ccIWiggX.s: Assembler messages:
> >> /tmp/ccIWiggX.s:22: Error: invalid literal constant: pool needs to be closer
> 
> This fixes the error reported by 0day build bot.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Fixes: 7e9bf33b8124 ("ARM: kprobes: Make a frame pointer on __kretprobe_trampoline")
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  arch/arm/probes/kprobes/core.c |   57 +++++++++++++++++++++-------------------
>  1 file changed, 30 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> index 4848404ba51b..51f1438456ae 100644
> --- a/arch/arm/probes/kprobes/core.c
> +++ b/arch/arm/probes/kprobes/core.c
> @@ -373,43 +373,46 @@ int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
>   * should be enough for stacktrace from the return handler with or
>   * without pt_regs.
>   */
> -void __naked __kprobes __kretprobe_trampoline(void)
> -{
> -	__asm__ __volatile__ (
> +asm(
> +	".text\n"
> +	".global __kretprobe_trampoline\n"
> +	".type __kretprobe_trampoline, %function\n"
> +	"__kretprobe_trampoline:\n"
>  #ifdef CONFIG_FRAME_POINTER
> -		"ldr	lr, =__kretprobe_trampoline	\n\t"
> +	"ldr	lr, =__kretprobe_trampoline	\n\t"
>  	/* __kretprobe_trampoline makes a framepointer on pt_regs. */
>  #ifdef CONFIG_CC_IS_CLANG
> -		"stmdb	sp, {sp, lr, pc}	\n\t"
> -		"sub	sp, sp, #12		\n\t"
> -		/* In clang case, pt_regs->ip = lr. */
> -		"stmdb	sp!, {r0 - r11, lr}	\n\t"
> -		/* fp points regs->r11 (fp) */
> -		"add	fp, sp,	#44		\n\t"
> +	"stmdb	sp, {sp, lr, pc}	\n\t"
> +	"sub	sp, sp, #12		\n\t"
> +	/* In clang case, pt_regs->ip = lr. */
> +	"stmdb	sp!, {r0 - r11, lr}	\n\t"
> +	/* fp points regs->r11 (fp) */
> +	"add	fp, sp,	#44		\n\t"
>  #else /* !CONFIG_CC_IS_CLANG */
> -		/* In gcc case, pt_regs->ip = fp. */
> -		"stmdb	sp, {fp, sp, lr, pc}	\n\t"
> -		"sub	sp, sp, #16		\n\t"
> -		"stmdb	sp!, {r0 - r11}		\n\t"
> -		/* fp points regs->r15 (pc) */
> -		"add	fp, sp, #60		\n\t"
> +	/* In gcc case, pt_regs->ip = fp. */
> +	"stmdb	sp, {fp, sp, lr, pc}	\n\t"
> +	"sub	sp, sp, #16		\n\t"
> +	"stmdb	sp!, {r0 - r11}		\n\t"
> +	/* fp points regs->r15 (pc) */
> +	"add	fp, sp, #60		\n\t"
>  #endif /* CONFIG_CC_IS_CLANG */
>  #else /* !CONFIG_FRAME_POINTER */
> -		"sub	sp, sp, #16		\n\t"
> -		"stmdb	sp!, {r0 - r11}		\n\t"
> +	"sub	sp, sp, #16		\n\t"
> +	"stmdb	sp!, {r0 - r11}		\n\t"
>  #endif /* CONFIG_FRAME_POINTER */
> -		"mov	r0, sp			\n\t"
> -		"bl	trampoline_handler	\n\t"
> -		"mov	lr, r0			\n\t"
> -		"ldmia	sp!, {r0 - r11}		\n\t"
> -		"add	sp, sp, #16		\n\t"
> +	"mov	r0, sp			\n\t"
> +	"bl	trampoline_handler	\n\t"
> +	"mov	lr, r0			\n\t"
> +	"ldmia	sp!, {r0 - r11}		\n\t"
> +	"add	sp, sp, #16		\n\t"
>  #ifdef CONFIG_THUMB2_KERNEL
> -		"bx	lr			\n\t"
> +	"bx	lr			\n\t"
>  #else
> -		"mov	pc, lr			\n\t"
> +	"mov	pc, lr			\n\t"
>  #endif
> -		: : : "memory");
> -}
> +	".size __kretprobe_trampoline, .-__kretprobe_trampoline\n"
> +);
> +NOKPROBE_SYMBOL(__kretprobe_trampoline);
>  
>  /* Called from __kretprobe_trampoline */
>  static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>