linux-kernel - Re: [PATCH] kprobes, x86/ptrace.h: fix regs argument order for i386

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Date:   Fri, 28 Aug 2020 13:59:54 +0200
From:   peterz@...radead.org
To:     Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@...il.com>
Cc:     mhiramat@...nel.org, rostedt@...dmis.org, mingo@...hat.com,
        davem@...emloft.net, oleg@...hat.com, naveen.n.rao@...ux.ibm.com,
        anil.s.keshavamurthy@...el.com, tglx@...utronix.de, bp@...en8.de,
        hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes, x86/ptrace.h: fix regs argument order for i386

On Fri, Aug 28, 2020 at 05:02:46PM +0530, Vamshi K Sthambamkadi wrote:
> On i386, the order of parameters passed on regs is eax,edx,and ecx
> (as per regparm(3) calling conventions).
> 
> Change the mapping in regs_get_kernel_argument(), so that arg1=ax
> arg2=dx, and arg3=cx.
> 
> Running the selftests testcase kprobes_args_use.tc shows the result
> as passed.
> 
Fixes: 3c88ee194c28 ("x86: ptrace: Add function argument access API")
> Signed-off-by: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@...il.com>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> ---
>  arch/x86/include/asm/ptrace.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
> index 40aa69d..d8324a2 100644
> --- a/arch/x86/include/asm/ptrace.h
> +++ b/arch/x86/include/asm/ptrace.h
> @@ -327,8 +327,8 @@ static inline unsigned long regs_get_kernel_argument(struct pt_regs *regs,
>  	static const unsigned int argument_offs[] = {
>  #ifdef __i386__
>  		offsetof(struct pt_regs, ax),
> -		offsetof(struct pt_regs, cx),
>  		offsetof(struct pt_regs, dx),
> +		offsetof(struct pt_regs, cx),
>  #define NR_REG_ARGUMENTS 3
>  #else
>  		offsetof(struct pt_regs, di),
> -- 
> 2.7.4
>