From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/2116 Path: news.gmane.org!not-for-mail From: boris brezillon Newsgroups: gmane.linux.lib.musl.general Subject: Re: TLS (thread-local storage) support Date: Tue, 16 Oct 2012 23:47:52 +0200 Message-ID: References: <20121004211332.GA12874@brightrain.aerifal.cx> <20121004223631.GL254@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1350424086 9357 80.91.229.3 (16 Oct 2012 21:48:06 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 16 Oct 2012 21:48:06 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-2117-gllmg-musl=m.gmane.org@lists.openwall.com Tue Oct 16 23:48:14 2012 Return-path: Envelope-to: gllmg-musl@plane.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1TOEzj-000576-S2 for gllmg-musl@plane.gmane.org; Tue, 16 Oct 2012 23:48:11 +0200 Original-Received: (qmail 17552 invoked by uid 550); 16 Oct 2012 21:48:04 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 17544 invoked from network); 16 Oct 2012 21:48:04 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; bh=NPRRgHhAxGu/N/yYhvZEVnlOqhGJDUkw5zekr+mRzR8=; b=jhx9AGqtEI1m3+46JBjefnhp9cHQQK70+VCPz0FH8qyMyjR7WKB8EiObGjOrhsqZoz t58a14xAgk81xp+7D4ZNntR1L5/mlZojxLnmqBYTzgXUTkl4MaemqYeLK5JP7/j+OjMz TwMCQ4znUyxydZ5BmTg8w3mcgB/jmxd+Y8V+ucTVSQ1MILhU0gKGeWzLTbpuXU1BK77U +bQ2Vl7D8sEJdgDhDLfGucwd6GJiT2rdOfeiTwtQ5b79y8PWn75G0KQNvHtqjWc4UIVr L/ZIzE4YYeIREcCepf2fg8v/XctQC5V+fc1M+EvjYS7ale4AG87fn/iw+2aaBVw45M7C C2Sg== In-Reply-To: Xref: news.gmane.org gmane.linux.lib.musl.general:2116 Archived-At: 2012/10/16 boris brezillon : > Hi, > > First I'd like to thank Rich for adding TLS support (I started to work > on it a few weeks ago but never had time to finish it). > > 2012/10/6 Daniel Cegie=C5=82ka : >> 2012/10/5 Rich Felker : >>> On Thu, Oct 04, 2012 at 11:29:11PM +0200, Daniel Cegie=C5=82ka wrote: >>>> great news! Finally able to compile Go (lang)... >>> >>> Did Go fail with gcc's emulated TLS in libgcc? >> >> I tested Go with sabotage (with fresh musl). I'll try to do it again... >> gcc in sabotage was compiled without support for TLS, so I didn't >> expect that it will be successful: >> >> https://github.com/rofl0r/sabotage/blob/master/pkg/gcc4 >> > There's at least one thing (maybe more) missing for go support with > musl : gcc 'split-stack' support (see http://blog.nella.org/?p=3D849 and > http://gcc.gnu.org/wiki/SplitStacks). > > I'm also interested in split stack support in musl but for other > reasons (thread and coroutine stack automatic expansion). > > For x86/x86_64 split stack is implemented using a field inside the > pthread struct which is accessed via %fs (or %gs for x86_64) and an > offset. > > Currently this offset is defined at 0x30 (0x70 for x86_64) by the > TARGET_THREAD_SPLIT_STACK_OFFSET but only if TARGET_LIBC_PROVIDES_SSP > is defined (see gcc/config/i386/gnu-user.h or > gcc/config/i386/gnu-user64.h). > > As far as I know musl does not support stack protection, but we could > at least patch gcc to define TARGET_THREAD_SPLIT_STACK_OFFSET when > using musl. > > We also need to reserve a field in the musl pthread struct. There are > currently two fields named 'unused1' and 'unused2' but I'm not sure > they're really unused in every supported arch. > > > BTW, I'd like to work on a more integrated support of split stack in MUSL= : > > 1) support in dynamic linker (see the last point of > http://gcc.gnu.org/wiki/SplitStacks) : check split stack notes in > shared libs (and program ?) > > 2) support in thread implementation : currently when a thread is > created the stack limit is set afterward (see > https://github.com/mirrors/gcc/blob/master/libgcc/generic-morestack-threa= d.c > and https://github.com/mirrors/gcc/blob/master/libgcc/config/i386/moresta= ck.S) > and the stack size is supposed to be 16K (which is the minimum stack > size). This means we may reallocate a new stack chunk even if the > previous one (the first one) is not fully used. > If stack limit is set by thread implementation, this can be set > appropriately according to the stack size defined by the thread > creator. > > 3) more optimizations I haven't thought about yet... > 4) Compile musl with '-fsplit-stack' and add no_split_stack attribute to appropriate functions (at least all functions called before pthread_self_init because %gs or %fs register is unusable before this call). 5) set main thread stack limit to 0 (pthread_self_init) : the main thread stack grow is handled by the kernel. 6) add no-split-stack note to every asm file. 7) make split stack support optional (either by checking the -fsplit-stack option in CFLAGS or with a specific option : --enable-split-stack) : split stack adds overhead to every functions (except for those with the 'no_split_stack' attribute). > Do you have any concern about adding those features in musl ? > > Let me know if you see other issues I haven't noticed. > > > Regards, > > Boris