Date: Wed, 9 Sep 2015 13:13:38 -0400 From: Rich Felker <dalias@...c.org> To: Zack Weinberg <zackw@...ix.com> Cc: gcc@....gnu.org, GNU C Library <libc-alpha@...rceware.org>, musl@...ts.openwall.com Subject: Re: Compiler support for erasure of sensitive data On Wed, Sep 09, 2015 at 12:47:10PM -0400, Zack Weinberg wrote: > On Wed, Sep 9, 2015 at 12:42 PM, Rich Felker <dalias@...c.org> wrote: > > You're making this harder than it needs to be. The "m" constraint is > > the wrong thing to use here. Simply use: > > > > __asm__(""::"r"(ptr):"memory"); > > Please review my earlier conversation with Adhemerval on exactly this point. My understanding is that you consider this a "big hammer". Does that really matter if the intent is that it only be used in isolated, sensitive contexts? Are you just unhappy with the performance cost, or concerned that the clobber will cause more spilling of sensitive data? I'm doubtful that this would happen because a "memory" clobber does not affect all data cached in registers, only data which is potentially reachable by the asm. In any case, I think the intent of my reply was unclear. I did not mean to detract from the idea of compiler support for handling of sensitive data, just to point out that the hack with the "m" constraint is wrong and easily fixed. It still may be possible to get much better results via other means. Rich
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.