From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/12840 Path: news.gmane.org!.POSTED!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: TLS issue on aarch64 Date: Sat, 26 May 2018 02:54:16 +0200 Message-ID: <20180526005415.GI4418@port70.net> References: <20180525145059.GG4418@port70.net> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1527295944 24907 195.159.176.226 (26 May 2018 00:52:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 26 May 2018 00:52:24 +0000 (UTC) User-Agent: Mutt/1.9.1 (2017-09-22) To: musl@lists.openwall.com Original-X-From: musl-return-12856-gllmg-musl=m.gmane.org@lists.openwall.com Sat May 26 02:52:20 2018 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 1fMNRT-0006N2-Dc for gllmg-musl@m.gmane.org; Sat, 26 May 2018 02:52:19 +0200 Original-Received: (qmail 5969 invoked by uid 550); 26 May 2018 00:54:28 -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 5951 invoked from network); 26 May 2018 00:54:27 -0000 Mail-Followup-To: musl@lists.openwall.com Content-Disposition: inline In-Reply-To: Xref: news.gmane.org gmane.linux.lib.musl.general:12840 Archived-At: * Phillip Berndt [2018-05-26 00:20:04 +0200]: > 2018-05-25 16:50 GMT+02:00 Szabolcs Nagy : > > i think the constraints for tp are: > > > > - tp must be aligned to 'tls_align' > > > > - tp must be at a small fixed offset from the end > > of pthread struct (so asm code can access the dtv) > > > > - tp + off must be usable memory for tls for off >= 16 > > (this is aarch64 specific) > > > > Hmm.. but these constraints do not explain the extra offset of one > alignment I'm seeing in the GCC output, do they? If I compile a tp must be aligned and tp + offset must be aligned too, but offset >= 16 has to hold. > program with a single TLS variable with > __attribute__((aligned(n)) that does nothing but try to reference and > print said variable, I get the > following assembler code from GCC: > > For n = 0x1000: > > 400194: d53bd041 mrs x1, tpidr_el0 > 400198: b0000040 adrp x0, 409000 <__subtf3+0xd18> > 40019c: 91400421 add x1, x1, #0x1, lsl #12 > 4001a0: 91000021 add x1, x1, #0x0 > > > For n = 0x100: > > 400194: d53bd041 mrs x1, tpidr_el0 > 400198: b0000040 adrp x0, 409000 <__subtf3+0xd18> > 40019c: 91400021 add x1, x1, #0x0, lsl #12 > 4001a0: 91040021 add x1, x1, #0x100 > > For n = 0x10: > > 400194: d53bd041 mrs x1, tpidr_el0 > 400198: b0000040 adrp x0, 409000 <__subtf3+0xd18> > 40019c: 91400021 add x1, x1, #0x0, lsl #12 > 4001a0: 91004021 add x1, x1, #0x10 > > That's how I came up with the mem += libc.tls_align hack in the first place. > indeed you need another alignment there, i came up with the following fix: (on mips/ppc i expect it not to change anything: tp is at a page aligned offset from the end of struct pthread, so one alignment is enough there, but on aarch64/arm/sh4 this makes a difference, and seems to pass my simple tests) diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c index 1c5d98a0..8e70024d 100644 --- a/src/env/__init_tls.c +++ b/src/env/__init_tls.c @@ -41,9 +41,12 @@ void *__copy_tls(unsigned char *mem) #ifdef TLS_ABOVE_TP dtv = (void **)(mem + libc.tls_size) - (libc.tls_cnt + 1); - mem += -((uintptr_t)mem + sizeof(struct pthread)) & (libc.tls_align-1); + /* Ensure TP is aligned. */ + mem += -(uintptr_t)TP_ADJ(mem) & (libc.tls_align-1); td = (pthread_t)mem; mem += sizeof(struct pthread); + /* Ensure TLS is aligned after struct pthread. */ + mem += -(uintptr_t)mem & (libc.tls_align-1); for (i=1, p=libc.tls_head; p; i++, p=p->next) { dtv[i] = mem + p->offset;