From patchwork Sat Mar 3 09:10:18 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Aurelien Jarno X-Patchwork-Id: 26171 Received: (qmail 42600 invoked by alias); 3 Mar 2018 09:10:35 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 42581 invoked by uid 89); 3 Mar 2018 09:10:34 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-25.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_LAZY_DOMAIN_SECURITY, T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy=Hx-languages-length:2278 X-HELO: hall.aurel32.net From: Aurelien Jarno To: libc-alpha@sourceware.org Cc: Aurelien Jarno Subject: [PATCH] sparc32: Add nop before __startcontext to stop unwinding [BZ #xxxxx] Date: Sat, 3 Mar 2018 10:10:18 +0100 Message-Id: <20180303091018.32019-1-aurelien@aurel32.net> On sparc32 tst-makecontext fails, as backtrace called within a context created by makecontext to yield infinite backtrace. Fix that the same way than nios2 by adding a nop just before __startcontext. This is needed as otherwise FDE lookup just repeatedly finds __setcontext's FDE in an infinite loop, due to the convention of using 'address - 1' for FDE lookup. Changelog: [BZ #22919] * sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S (__startcontext): Add nop before __startcontext, add explaining comments. --- ChangeLog | 6 ++++++ sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S | 13 +++++++++++++ 2 files changed, 19 insertions(+) diff --git a/ChangeLog b/ChangeLog index 4b7e0a0261..6216817498 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2018-03-03 Aurelien Jarno + + [BZ #22919] + * sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S (__startcontext): + Add nop before __startcontext, add explaining comments. + 2018-03-01 Maciej W. Rozycki * nptl_db/td_ta_thr_iter.c (iterate_thread_list): Remove diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S b/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S index 695f172c63..283aef1b30 100644 --- a/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S +++ b/sysdeps/unix/sysv/linux/sparc/sparc32/setcontext.S @@ -95,6 +95,19 @@ END(__setcontext) weak_alias (__setcontext, setcontext) +/* We add an NOP here to separate between __setcontext/__startcontext. The + wanted behavior that happens is: when unwinding from a function called + inside a makecontext() context, FDE lookup will use '&__startcontext - 1', + then returns NULL for no FDE found, and immediately ends the unwind, in + a normal fashion. + + If this NOP word does not exist, FDE lookup just repeatedly finds + __setcontext's FDE in an infinite loop, due to the convention of using + 'address - 1' for FDE lookup. Modifiying/deleting the below + __startcontext's FDE has no help on this. */ + + nop + /* This is the helper code which gets called if a function which is registered with 'makecontext' returns. In this case we have to install the context listed in the uc_link element of the context