linux-kernel - Re: [patch 4/7] Immediate Values

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 for Android: free password hash cracker in your pocket

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

Message-ID: <46F04D53.6040903@zytor.com>
Date:	Tue, 18 Sep 2007 15:12:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@....de>, Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 4/7] Immediate Values - i386 Optimization

Jeremy Fitzhardinge wrote:
> Mathieu Desnoyers wrote:
> 
>> +#define immediate_read(name)						\
>> +	({								\
>> +		__typeof__(name##__immediate) value;			\
>> +		switch (sizeof(value)) {				\
>> +		case 1:							\
>> +			asm (	".section __immediate, \"a\", @progbits;\n\t" \
>> +					".long %1, (0f)+1, 1;\n\t"	\
>> +					".previous;\n\t"		\
>> +					"0:\n\t"			\
>> +					"mov %2,%0;\n\t"		\
> 
> Given that you're relying on the exact instruction that this mov
> generates, it might be better to explicitly put the opcodes in with
> .byte.  That way you're protected from the assembler deciding to
> generate some other form of the instruction (for whatever reason).  I
> guess substituting in different registers would be a pain.

Allowing different registers should be doable, but if so, one would have
to put 0: at the *end* of the instruction and use (0f)-4 instead, since
the non-%eax forms are one byte longer.

This also seems "safer", since an imm32 is always the last thing in the
instruction.

	-hpa

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/