From: dave.long@linaro•org (David Long)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v4 13/16] ARM: Add an emulate flag to the kprobes/uprobes instruction decode functions
Date: Thu, 16 Jan 2014 13:12:32 -0500 [thread overview]
Message-ID: <52D82110.9020309@linaro.org> (raw)
In-Reply-To: <1389863932.3530.12.camel@linaro1.home>
On 01/16/14 04:18, Jon Medhurst (Tixy) wrote:
> On Wed, 2014-01-15 at 14:31 -0500, David Long wrote:
>> On 12/20/13 09:58, Jon Medhurst (Tixy) wrote:
>>> On Sun, 2013-12-15 at 23:08 -0500, David Long wrote:
> [...]
>>>> {
>>>> #ifdef CONFIG_THUMB2_KERNEL
>>>> if (thumb) {
>>>> @@ -253,7 +253,7 @@ set_emulated_insn(probes_opcode_t insn, struct arch_specific_insn *asi,
>>>> * non-zero value, the corresponding nibble in pinsn is validated and modified
>>>> * according to the type.
>>>> */
>>>> -static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs)
>>>> +static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
>>>> {
>>>> probes_opcode_t insn = *pinsn;
>>>> probes_opcode_t mask = 0xf; /* Start at least significant nibble */
>>>> @@ -317,9 +317,16 @@ static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs)
>>>> /* Replace value of nibble with new register number... */
>>>> insn &= ~mask;
>>>> insn |= new_bits & mask;
>>>> + if (modify) {
>>>> + /* Replace value of nibble with new register number */
>>>> + insn &= ~mask;
>>>> + insn |= new_bits & mask;
>>>> + }
>>>
>>> Huh? As is, the above addition doesn't do anything because insn has
>>> already been modified. I guess you played with the idea that you needed
>>> to avoid changing insn (you don't) and then didn't undo the experiment
>>> quite right. :-)
>>>
>>
>> The conditional modification of the instruction was part of Rabin's
>> original work for uprobes, but I messed up the merge from an earlier
>> working version of my patches. My intention was/is to delete the old
>> unconditional code. Sounds like maybe you disagree though. The intent
>> is to only modify the instruction in the kprobes case.
>
> 'insn' is the local variable containing the instruction value we're
> processing. It doesn't matter if we change that, we just need to avoid
> updating the instruction in memory, which the code in the next chunk
> already correctly checks for...
>
>>>> }
>>>>
>>>> - *pinsn = insn;
>>>> + if (modify)
>>>> + *pinsn = insn;
>>>> +
>>>> return true;
>>>>
>
> So only one of these 'if (modify)' checks is required for code
> correctness, and I suggest keeping the second one as it's more explicit
> and defensive.
>
>
OK, I see your point. I shall simplify the code as you have suggested.
-dl
next prev parent reply other threads:[~2014-01-16 18:12 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-16 4:08 [PATCH v4 00/16] uprobes: Add uprobes support for ARM David Long
2013-12-16 4:08 ` [PATCH v4 01/16] uprobes: allow ignoring of probe hits David Long
2013-12-16 4:08 ` [PATCH v4 02/16] ARM: move shared uprobe/kprobe definitions into new include file David Long
2013-12-20 12:46 ` Jon Medhurst (Tixy)
2014-01-15 16:43 ` David Long
2013-12-16 4:08 ` [PATCH v4 03/16] ARM: Move generic arm instruction parsing code to new files for sharing between features David Long
2013-12-16 4:08 ` [PATCH v4 04/16] ARM: move generic thumb instruction parsing code to new files for use by other feature David Long
2013-12-20 12:46 ` Jon Medhurst (Tixy)
2014-01-15 16:41 ` David Long
2013-12-16 4:08 ` [PATCH v4 05/16] ARM: use a function table for determining instruction interpreter actions David Long
2013-12-20 12:45 ` Jon Medhurst (Tixy)
2014-01-15 16:25 ` David Long
2013-12-16 4:08 ` [PATCH v4 06/16] ARM: Disable jprobes test when built into thumb-mode kernel David Long
2013-12-16 4:08 ` [PATCH v4 07/16] ARM: Remove use of struct kprobe from generic probes code David Long
2013-12-20 13:55 ` Jon Medhurst (Tixy)
2014-01-15 16:44 ` David Long
2013-12-16 4:08 ` [PATCH v4 08/16] ARM: Use new opcode type in ARM kprobes/uprobes code David Long
2013-12-16 4:08 ` [PATCH v4 09/16] ARM: Make the kprobes condition_check symbol names more generic David Long
2013-12-16 4:08 ` [PATCH v4 10/16] ARM: Change more ARM kprobes symbol names to something more David Long
2013-12-16 4:08 ` [PATCH v4 11/16] ARM: Rename the shared kprobes/uprobe return value enum David Long
2013-12-16 4:08 ` [PATCH v4 12/16] ARM: Change the remaining shared kprobes/uprobes symbols to something generic David Long
2013-12-16 4:08 ` [PATCH v4 13/16] ARM: Add an emulate flag to the kprobes/uprobes instruction decode functions David Long
2013-12-20 14:58 ` Jon Medhurst (Tixy)
2014-01-15 19:31 ` David Long
2014-01-16 9:18 ` Jon Medhurst (Tixy)
2014-01-16 18:12 ` David Long [this message]
2013-12-16 4:08 ` [PATCH v4 14/16] ARM: Make arch_specific_insn a define for new arch_probes_insn structure David Long
2013-12-16 4:08 ` [PATCH v4 15/16] ARM: add uprobes support David Long
2013-12-20 18:34 ` Jon Medhurst (Tixy)
2013-12-20 19:00 ` Rabin Vincent
2013-12-20 19:47 ` Jon Medhurst (Tixy)
2013-12-23 15:32 ` Oleg Nesterov
2014-01-21 16:51 ` David Long
2013-12-16 4:08 ` [PATCH v4 16/16] ARM: Remove uprobes dependency on kprobes David Long
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