linux-kernel - Re: [patch 2/8] compiler-gcc.h: add more comments to RELOC

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

Message-ID: <Pine.LNX.4.64.0901161433410.27177@quilx.com>
Date:	Fri, 16 Jan 2009 14:37:32 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Richard Henderson <rth@...ddle.net>
cc:	Rusty Russell <rusty@...tcorp.com.au>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	andi@...stfloor.org, ak@...ux.intel.com, sfr@...b.auug.org.au,
	travis@....com, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/8] compiler-gcc.h: add more comments to RELOC_HIDE

On Thu, 15 Jan 2009, Richard Henderson wrote:

> I didn't explore the space of possible solutions, merely gave Rusty a solution
> that I knew would work, and would never fail because the compiler would never
> look through the asm.
>
> I wouldn't be surprised if the compiler thought "(long)&foo - large_constant"
> could be put back together into a small-data relocation, simply because at the
> level at which that optimization is performed, we've thrown away type data
> like long and void*; we only have modes.

We are talking about

(long)&foo + long_variable

Are you saying that the compiler will be ignoring the high bits in
variable because of the size of foo?

> Why are you wanting to change this at all?  It works as it is.

It looks like its useless and more an indication of either a broken
compiler or wrong assumptions about the compiler. Removing RELOC_HIDE
should allow the compiler to freely optimize the per cpu address
calculations.
--
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/