From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=0.4 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 33711200B9 for ; Mon, 7 May 2018 13:58:10 +0000 (UTC) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; q=dns; s=default; b=BzApZSsuwqPJIeGl Zv8hf5pfcQri8OEsKkvMRyCdFz7/XmhIDwlAEkpvIPiA3FfMZ7yk1wSMrNPu4iXP TnpDQYN1daiCulDoYCFFAadhxaaOEpVF4jj9PT7/9VOpFU7SB5OY0pbEcTJ/aHX4 5NXDx4pReZOa/fSlaaxsI7KCc3k= DKIM-Signature: v=1; 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bh=z8aOCQtjIm34jb5GhdgkbNut8ZSHi0JKqYvZOoy67Po=; b=pworp4/3WUAAC/ugzCijBnK3dSd3cQOSs9iM0C8cXEa3wtWWhUMfT677pvOFkD5dY7 pcMHbr1wqkyCZ9Lx2EK+mbKoa+jLXph9/jlVwhjCVv6W4uNhNzQTtmxKanlVdZcPUVg9 HnQGFp2nzwnKvxh10VAc6WGtpZFke8xtW2jJD2OCY2AoMy+PGrsMrmhwCZA7UFccRSKb Hxldf4kVhdwJVxvbK1hl1axLK10szayLUopHYbtog/y3yZnUpfg/rP9DZA5fk9+h9ShJ 7MTnfNvX8r9p2oGOdJE1Pcjy73782OziMk0ZUtwysyOFFyLCs2vuoifP4ssnLd8B1EHV FXTA== X-Gm-Message-State: ALQs6tBZdgk1oziksrwa278eu3yCK9yr9/kSoEL1wwjnM5jJQ4jfbp3y p6z2x5PhVo2MkLVREQL5M6JAaQUgfXA= X-Google-Smtp-Source: AB8JxZpZFWfo4BuYsMOLMipUX/qc9s+BtMbNeFMcxwk/TM2S3IuUW2q6e7zmGeMKfBX7O0iRB4Ug9Q== X-Received: by 10.55.215.140 with SMTP id t12mr32115355qkt.148.1525701483544; Mon, 07 May 2018 06:58:03 -0700 (PDT) Subject: Re: [PATCH v2 01/21] powerpc: Create stackframe information on syscall To: Zack Weinberg , libc-alpha@sourceware.org References: <1519679016-12241-2-git-send-email-adhemerval.zanella@linaro.org> <20180507024909.5598-1-zackw@panix.com> From: Adhemerval Zanella Openpgp: preference=signencrypt Autocrypt: addr=adhemerval.zanella@linaro.org; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180507024909.5598-1-zackw@panix.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit On 06/05/2018 23:49, Zack Weinberg wrote: > On 26 Feb 2018, Adhemerval Zanella wrote: >> This patch adds a minimal stackframe creation on powerpc syscall >> implementation so backtrace works correctly on a signal handler. > > I don't know powerpc well enough to know if this should be necessary. > I think one of the powerpc arch maintainers should comment. I do have > a couple questions: > >> +#ifdef __powerpc64__ >> + stdu r1, -FRAME_MIN_SIZE (r1) >> + cfi_adjust_cfa_offset (FRAME_MIN_SIZE) >> +#else >> + stwu r1,-16(1) >> + cfi_def_cfa_offset (16) >> +#endif > > Why does this use cfa_adjust_cfa_offset for 64-bit but _def_ for 32-bit? I am not well versed in CFI definition, so I was basically followed what compiler is spilling in a usual function call back when I coded it. > >> +#ifdef __powerpc64__ >> + addi r1, r1, FRAME_MIN_SIZE >> +#else >> + addi r1,r1,16 >> +#endif > > If FRAME_MIN_SIZE were defined for ppc32, we could reduce the > ifdeffage here. > >> + cfi_def_cfa_offset (0) >> sc >> PSEUDO_RET > > Shouldn't the stack adjustments be undone _after_ the 'sc' > instruction? Actually, is it possible that a single > cfi_def_cfa_offset (0) at the beginning of the function is all that's > really needed here? It seems like backtrace should be able to handle > leaf frames in general... Indeed the single 'cfi_def_cfa_offset (0)' is suffice, I will change the patch accordingly in next iteration.