linux-kernel - Re: [PATCH v15 01/10] arm64: Add HAVE_REGS_AND_STACK_ACCESS

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Message-ID: <57892286.1040609@linaro.org>
Date:	Fri, 15 Jul 2016 13:51:02 -0400
From:	David Long <dave.long@...aro.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Mark Rutland <mark.rutland@....com>,
	Petr Mladek <pmladek@...e.com>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	Will Deacon <will.deacon@....com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	yalin wang <yalin.wang2010@...il.com>,
	Li Bin <huawei.libin@...wei.com>,
	John Blackwood <john.blackwood@...r.com>,
	Pratyush Anand <panand@...hat.com>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Huang Shijie <shijie.huang@....com>,
	Dave P Martin <Dave.Martin@....com>,
	Jisheng Zhang <jszhang@...vell.com>,
	Vladimir Murzin <Vladimir.Murzin@....com>,
	Steve Capper <steve.capper@...aro.org>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Yang Shi <yang.shi@...aro.org>,
	Mark Brown <broonie@...nel.org>,
	Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
	William Cohen <wcohen@...hat.com>,
	Alex Bennée <alex.bennee@...aro.org>,
	Adam Buchbinder <adam.buchbinder@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	linux-kernel@...r.kernel.org, James Morse <james.morse@....com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robin Murphy <robin.murphy@....com>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [PATCH v15 01/10] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API
 feature

On 07/15/2016 11:13 AM, Catalin Marinas wrote:
> On Fri, Jul 15, 2016 at 10:51:23AM -0400, David Long wrote:
>> On 07/15/2016 06:57 AM, Catalin Marinas wrote:
>>> On Fri, Jul 08, 2016 at 12:35:45PM -0400, David Long wrote:
>>>> --- a/arch/arm64/include/asm/ptrace.h
>>>> +++ b/arch/arm64/include/asm/ptrace.h
>>>> @@ -74,6 +74,7 @@
>>>>    #define COMPAT_PT_DATA_ADDR		0x10004
>>>>    #define COMPAT_PT_TEXT_END_ADDR		0x10008
>>>>    #ifndef __ASSEMBLY__
>>>> +#include <linux/bug.h>
>>>>
>>>>    /* sizeof(struct user) for AArch32 */
>>>>    #define COMPAT_USER_SZ	296
>>>> @@ -119,6 +120,8 @@ struct pt_regs {
>>>>    	u64 syscallno;
>>>>    };
>>>>
>>>> +#define MAX_REG_OFFSET offsetof(struct pt_regs, pstate)
>>>> +
>>>>    #define arch_has_single_step()	(1)
>>>>
>>>>    #ifdef CONFIG_COMPAT
>>>> @@ -147,6 +150,55 @@ struct pt_regs {
>>>>    #define user_stack_pointer(regs) \
>>>>    	(!compat_user_mode(regs) ? (regs)->sp : (regs)->compat_sp)
>>>>
>>>> +extern int regs_query_register_offset(const char *name);
>>>> +extern const char *regs_query_register_name(unsigned int offset);
>>>
>>> Is regs_query_register_offset() used anywhere? I grep'ed the kernel with
>>> these patches applied but couldnperf_regs.c't find any use.
>>
>> It's referenced in kernel/trace/trace_probe.c.
>
> I meant regs_query_register_name() (vim completion wrote the first one).
>

I had assumed it was used by kgdb to provide human-readable register 
names for debugger output, but apparently that is handled inside the 
kgdb.c stub for each architecture. I can only assume this is currently 
provided in all (or at least most) architectures because some code 
outside the kernel tree needs (or used to need?) to be able to do the 
reverse of regs_query_register_offset(). It's easy enough to remove 
this, but that will make arm64 unlike the other architectures in its 
CONFIG_HAVE_REGS_AND_STACK_ACCESS_API support.

>>>> +extern bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr);
>>>
>>> This one only seems to be used in arch/arm64/kernel/ptrace.c. Can we
>>> make it static and remove the declaration?
>>
>> OK.
>
> I can change it locally.

It's looking like there will need to be another iteration of the patch 
for a few small things anyway, although those changes could also be done 
as subsequent improvements.

>
> Are these going to be used in the future by uprobes?
>

It would appear not.

Thanks,
-dl