linux-kernel - Re: [PATCH v5 7/9] riscv/kprobe: Prepare detour buffer for optimized kprobe

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <4062e65d-f411-bc01-d789-afee3c4b5b99@huawei.com>
Date:   Thu, 5 Jan 2023 08:46:07 +0800
From:   "liaochang (A)" <liaochang1@...wei.com>
To:     Björn Töpel <bjorn@...nel.org>,
        Chen Guokai <chenguokai17@...ls.ucas.ac.cn>,
        <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <rostedt@...dmis.org>, <mingo@...hat.com>,
        <sfr@...b.auug.org.au>
CC:     <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 7/9] riscv/kprobe: Prepare detour buffer for optimized
 kprobe



在 2023/1/4 17:12, Björn Töpel 写道:
> "liaochang (A)" <liaochang1@...wei.com> writes:
> 
>>>> +SYM_ENTRY(optprobe_template_insn, SYM_L_GLOBAL, SYM_A_NONE)
>>>> +	/*
>>>> +	 * Step3:
>>>> +	 * NOPS will be replaced by the probed instruction, at worst case 3 RVC
>>>> +	 * and 1 RVI instructions is about to execute out of line.
>>>> +	 */
>>>> +	nop
>>>
>>> A nop here will be either a compressed nop or a non-compressed,
>>> depending on the build (C-enabled or not), right? Maybe be explicit to
>>> the assembler what you want?
>>>
>>
>> You are right, if CONFIG_RISCV_ISA_C is disabled, two NOP is enough for 2 RVI execute out of line,
>> if CONFIG_RISCV_ISA_C is enabled, it needs eight C.NOP here for the worst case (3 RVC + 1 RVI).
>>
>> I will use {C}.NOP explicitly for different configure in next revision, thanks.
> 
> What I meant was that "nop" can expand to compressed instructions, and
> you should be explicit. So you know how it's expanded by the
> compiler/assembler.
> 
> An example:
> 
> $ cat bar.S
> 	.text
> bar:
> 	nop
> 	nop
> $ riscv64-linux-gnu-gcc -O2 -o bar.o -c bar.S && riscv64-linux-gnu-objdump -M no-aliases -d bar.o
> 
> bar.o:     file format elf64-littleriscv
> 
> 
> Disassembly of section .text:
> 
> 0000000000000000 <bar>:
>    0:	0001                	c.addi	zero,0
>    2:	0001                	c.addi	zero,0
> 
> 
> vs
> 
> $ cat foo.S
> 	.text
> foo:
> 	.option norvc
> 	nop
> 	nop
> 
> $ riscv64-linux-gnu-gcc -O2 -o foo.o -c foo.S && riscv64-linux-gnu-objdump -M no-aliases -d foo.o
> 
> foo.o:     file format elf64-littleriscv
> 
> 
> Disassembly of section .text:
> 
> 0000000000000000 <foo>:
>    0:	00000013          	addi	zero,zero,0
>    4:	00000013          	addi	zero,zero,0

Above examples are very clear, i will use these expaned instructions in next revision, thanks.

> 
> 
> Björn

-- 
BR,
Liao, Chang