linux-kernel - Re: [PATCH 03/13] x86/paravirt: Convert native patch assembly code strings to macros

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Date:   Fri, 17 Nov 2017 20:10:13 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...izon.com>,
        live-patching@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mike Galbraith <efault@....de>,
        Chris Wright <chrisw@...s-sol.org>,
        Alok Kataria <akataria@...are.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        virtualization@...ts.linux-foundation.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 03/13] x86/paravirt: Convert native patch assembly code
 strings to macros

On 17/11/17 19:07, Borislav Petkov wrote:
> On Wed, Oct 04, 2017 at 10:58:24AM -0500, Josh Poimboeuf wrote:
>> Convert the hard-coded native patch assembly code strings to macros to
>> facilitate sharing common code between 32-bit and 64-bit.
>>
>> These macros will also be used by a future patch which requires the GCC
>> extended asm syntax of two '%' characters instead of one when specifying
>> a register name.
>>
>> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
>> ---
>>  arch/x86/include/asm/special_insns.h | 24 ++++++++++++++++++++++++
>>  arch/x86/kernel/paravirt_patch_32.c  | 21 +++++++++++----------
>>  arch/x86/kernel/paravirt_patch_64.c  | 29 +++++++++++++++--------------
>>  3 files changed, 50 insertions(+), 24 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
>> index ac402c6fc24b..0549c5f2c1b3 100644
>> --- a/arch/x86/include/asm/special_insns.h
>> +++ b/arch/x86/include/asm/special_insns.h
>> @@ -6,6 +6,30 @@
>>  
>>  #include <asm/nops.h>
>>  
>> +#ifdef CONFIG_X86_64
>> +# define _REG_ARG1			"%rdi"
>> +# define NATIVE_IDENTITY_32		"mov %edi, %eax"
> 
> Yeah, that "identity" looks strange. How about NATIVE_NOOP and
> NATIVE_NOOP_32 ?

Those are not NOPs. They return the identical value which was passed to
them. So identity isn't a bad name after all.

> 
>> +# define NATIVE_USERGS_SYSRET64		"swapgs; sysretq"
>> +#else
>> +# define _REG_ARG1			"%eax"
>> +#endif
>> +
>> +#define _REG_RET			"%" _ASM_AX
>> +
>> +#define NATIVE_ZERO			"xor " _REG_ARG1 ", " _REG_ARG1
> 
> NATIVE_ZERO_OUT
> 
> I guess. NATIVE_ZERO reads like the native representation of 0 :-)

NATIVE_ZERO_ARG1?


Juergen