From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/12037 Path: news.gmane.org!.POSTED!not-for-mail From: Adhemerval Zanella Newsgroups: gmane.linux.lib.musl.general Subject: Re: How to handle attempts to combine ARM Thumb with frame pointers? Date: Thu, 26 Oct 2017 16:46:04 -0200 Message-ID: References: <20171008032153.GH1627@brightrain.aerifal.cx> <20171025211623.GU15263@port70.net> <20171026170054.GA1627@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: blaine.gmane.org 1509043600 15900 195.159.176.226 (26 Oct 2017 18:46:40 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 26 Oct 2017 18:46:40 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 To: musl@lists.openwall.com Original-X-From: musl-return-12050-gllmg-musl=m.gmane.org@lists.openwall.com Thu Oct 26 20:46:30 2017 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1e7nAX-0001ol-45 for gllmg-musl@m.gmane.org; Thu, 26 Oct 2017 20:46:17 +0200 Original-Received: (qmail 11509 invoked by uid 550); 26 Oct 2017 18:46:22 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 11485 invoked from network); 26 Oct 2017 18:46:21 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=gxBF+52VcYOXGC46ccIbcEmhwZuTArtYBnBkoj/u+ao=; b=Rla5eQTdZblfMAyJEXoKtUvt3QPJql0pVD854olJl6+M+a6ow9fxEPFiO3N8VpbEJe DjfjJe2mYrCOMTF9YTUpavV01wTdUqYlQoDxNeZoBaHeCJtYozL8+w/DyFAtCkJuOGY3 IG2nu072AeiBDy8eL1GeWOpLSDf8Iyv+Xiy7s= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=gxBF+52VcYOXGC46ccIbcEmhwZuTArtYBnBkoj/u+ao=; b=X3nRLkzjQlOj25f8JqUOVqv4c7I68xMyYUQd2d6KMRYQ+Xx/vkzD2j8yRlQshraPXs ZMi5gzD5w6dCBACo34naxzdPw/bCpqYqpRziT6NTh1AP0zjL0BykRTW0oUkk1zpe2m+9 pMchGRqQKIYBschwSiXDzCbJkvJ67l0sWZxL9GeKcslJ9aIVaCYPpLWfgELwIMABrVJM S3O1KzvmB7FddM4aetOoTmfFsn/LRxst2yrxNX2PWf4JnkMl/Q1qel6x0fSJn+z0w6on 3hEUoEfhGYpmp+xVE4hiUnFLdxlo9e9IUaHK+tdZVPzokn8H8LXxnBx6nUzSbThVEsza ZGqw== X-Gm-Message-State: AMCzsaUrMoC3fcjfpqjcVXgywMn+jelHT3U2G09ov16zhIUYZFFKaF4+ RSWKYg5TuqHu/HIsA3KAwUgY0qV4fs8= X-Google-Smtp-Source: ABhQp+R8FpJ3QlBacTh4u2rrWzbQrU1E1CU0JRPGcXtrFXGLHLA3kOFCCS71NtQDUrzz9+nCL9Ljfg== X-Received: by 10.200.0.131 with SMTP id c3mr35222146qtg.221.1509043569109; Thu, 26 Oct 2017 11:46:09 -0700 (PDT) In-Reply-To: <20171026170054.GA1627@brightrain.aerifal.cx> Content-Language: en-GB Xref: news.gmane.org gmane.linux.lib.musl.general:12037 Archived-At: On 26/10/2017 15:00, Rich Felker wrote: > On Thu, Oct 26, 2017 at 02:48:11PM -0200, Adhemerval Zanella wrote: >> >> >> On 25/10/2017 19:16, Szabolcs Nagy wrote: >>> * Andre McCurdy [2017-10-09 09:48:29 -0700]: >>>> On Sat, Oct 7, 2017 at 8:21 PM, Rich Felker wrote: >>>>> On Fri, Oct 06, 2017 at 05:53:38PM -0700, Andre McCurdy wrote: >>>>> If you do want to test for broken configurations, rather than >>>>> hard-coding an assumption that some configuration is broken, you >>>>> should test for it. This would look something like, if ARCH is arm, >>>>> try compiling a trivial function with inline asm using r7 and see if >>>>> it fails. >>>> >>>> Yes, I came to the same conclusion after seeing the clang bug, which >>>> seems to suggest that clang uses a frame pointer even with >>>> optimisation enabled. >>>> >>>>> If so, exit with an error or perhaps try adding >>>>> -fomit-frame-pointer and retrying. >>>> >>>> If we over-ride the user supplied CFLAGS then there's probably no need >>>> to test the behaviour of the compiler - we can just force >>>> -fomit-frame-pointer unconditionally when compiling for Thumb/Thumb2. >>>> >>>> There's a slight complication though that if -fno-omit-frame-pointer >>>> is present in the user supplied CFLAGS then adding >>>> -fomit-frame-pointer to CFLAGS_AUTO won't over-ride it (since CFLAGS >>>> appears on the final compiler command line after CFLAGS_AUTO). >>>> >>>> Would it be OK for the configure script to append to CFLAGS? Or should >>>> the configure script perhaps setup a new variable (CFLAGS_FORCE?) >>>> which the Makefile would then add to CFLAGS_ALL after CFLAGS? >>>> >>> >>> glibc works this around in thumb mode by extern syscall asm >>> (of course it cannot guarantee that r7 is a frame pointer at >>> all times, an interrupt can observe r7 with syscall num in it, >>> i'm not sure if that's acceptable for users who compile with >>> frame-pointers, in musl there is some asm code which wont >>> have fp setup anyway). >>> >>> http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/arm/sysdep.h;h=6a64351cdd87c2041d639a17efc9f681262d5e3f;hb=HEAD#l335 >>> >> >> Why do you mean by glibc strategy might not be acceptable? What >> kind of issue are you referring on interrupt case? > > If you're compiling with frame pointers because you want them to be > present (and always valid) for debugging purposes or similar, there's > no way to achieve that while making syscalls -- and the most likely > place for a process to get stopped debugging is usually at a syscall. > Maybe this doesn't matter. It's not something we can change, just an > observation about a problem with the ABI, I think. I think this might be a problem for musl where it does not provide unwind information through CFI. For debugging with GLIBC, afaik GDB will these information along libgcc unwind symbols to get correct call frame and libc-do-syscall.S does seems to have correct CFI annotations. > > I think what we could do to ensure that compiling with frame pointers > otherwise works is add a configure test for use of r7 in inline asm, > and if it fails, -D something that would cause arch/arm/syscall_arch.h > not to define any syscall inlines but instead #define > SYSCALL_NO_INLINE which results in src/internal/syscall.h just using > the external __syscall function (which will of course clobber r7 for > the duration of the syscall). > > Rich >