From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 865 invoked by alias); 28 May 2015 18:34:18 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 816 invoked by uid 89); 28 May 2015 18:34:17 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.0 required=5.0 tests=AWL,BAYES_00,KAM_ASCII_DIVIDERS,KAM_STOCKGEN,RCVD_IN_DNSWL_LOW,SPF_PASS,T_RP_MATCHES_RCVD autolearn=no version=3.3.2 X-HELO: mail-vn0-f44.google.com Received: from mail-vn0-f44.google.com (HELO mail-vn0-f44.google.com) (209.85.216.44) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Thu, 28 May 2015 18:34:15 +0000 Received: by vnbg7 with SMTP id g7so5754616vnb.12 for ; Thu, 28 May 2015 11:34:13 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=B73Vz/HA9U2udo1dlijc8KQWbOvX90+K3wjWR+IDof4=; b=CmEXhnWO3vdCQOK8gu3KmQhq7KSQBCuY74b9TrhMz3JRCvjHnSgsSRXHSh/GNhb6e+ 6l2qvxl7D8f4WSoZSpen4Ciu11vPa2JN3Kjb9namNAYHUw1n6GhgExwedE/nyt8DaI4i +qbB9AwsmLdmWqSUdE0QBYIcQ6fjvWMSF5xwEddLZkAaV42g8rrMe240Ybh+dUMqED9l k+A+qvwn6KLV3zlTLWJUmT339BWRwxokluSJTMRgvx/9ROzGy9U4GfXgIBSN/NfZq3Ku 1z9UvypoyCswnUMcY++UVCAMx+LO9vxKwl6nZXpAlNSD5PBb/6mvwewHbN5u/WjWxh1V RQ/g== X-Gm-Message-State: ALoCoQm8bpm4vOjYmWvuA9kL1olg/0wa59bxvKlYKnDKPGYYI/S4jHzgaTMHvavsPD8Fk3IiHih+ MIME-Version: 1.0 X-Received: by 10.52.240.198 with SMTP id wc6mr3615862vdc.34.1432838053232; Thu, 28 May 2015 11:34:13 -0700 (PDT) Received: by 10.52.229.196 with HTTP; Thu, 28 May 2015 11:34:13 -0700 (PDT) In-Reply-To: <555EF018.2050309@redhat.com> References: <555E5376.3060706@redhat.com> <555EF018.2050309@redhat.com> Date: Thu, 28 May 2015 18:53:00 -0000 Message-ID: Subject: Re: [RFC][PATCH][X86_64] Eliminate PLT stubs for specified external functions via -fno-plt= From: Sriraman Tallam To: Pedro Alves Cc: "H.J. Lu" , Michael Matz , David Li , GCC Patches , Jan Hubicka Content-Type: multipart/mixed; boundary=20cf307810b22f5d4c0517289b94 X-IsSubscribed: yes X-SW-Source: 2015-05/txt/msg02683.txt.bz2 --20cf307810b22f5d4c0517289b94 Content-Type: text/plain; charset=UTF-8 Content-length: 2132 I have attached a patch that adds the new attribute "noplt". Please review. * config/i386/i386.c (avoid_plt_to_call): New function. (ix86_output_call_insn): Generate indirect call for functions marked with "noplt" attribute. (attribute_spec ix86_attribute_): Define new attribute "noplt". * doc/extend.texi: Document new attribute "noplt". * gcc.target/i386/noplt-1.c: New testcase. * gcc.target/i386/noplt-2.c: New testcase. Thanks Sri On Fri, May 22, 2015 at 2:00 AM, Pedro Alves wrote: > On 05/21/2015 11:02 PM, Sriraman Tallam wrote: >> On Thu, May 21, 2015 at 2:51 PM, Pedro Alves wrote: >>> On 05/21/2015 10:12 PM, Sriraman Tallam wrote: >>>> >>>> My original proposal, for x86_64 only, was to add >>>> -fno-plt=. This lets the user decide for which >>>> functions PLT must be avoided. Let the compiler always generate an >>>> indirect call using call *func@GOTPCREL(%rip). We could do this for >>>> non-PIC code too. No need for linker fixups since this relies on the >>>> user to know that func is from a shared object. >>> >>> Having to pass function names on the command line seems like an odd >>> interface. E.g, you'll need to pass the mangled name for >>> C++ functions. Any reason this isn't a function attribute? >> >> It is not clear to me where I would stick the attribute. Example >> usage in foo.cc: >> >> #include >> >> int main() { >> int n = memcmp(....); >> } >> >> I want memcmp to not go through PLT, do you propose explicitly >> re-declaring it in foo.cc with the attribute? > > I guess you'd do: > > #include > > __attribute__((no_plt)) typeof (memcpy) memcpy; > > int main() { > int n = memcmp(....); > } > > or even: > > #include > > int main() { > if (hotpath) { > __attribute__((no_plt)) typeof (memcpy) memcpy; > for (..) { > int n = memcmp(....); > } > } else { > int n = memcmp(....); > } > } > > or globally: > > $ cat no-plt/string.h: > #include_next > __attribute__((no_plt)) typeof (memcpy) memcpy; > > $ gcc -I no-plt/ ... > > Thanks, > Pedro Alves > --20cf307810b22f5d4c0517289b94 Content-Type: text/plain; charset=US-ASCII; name="noplt_attrib_patch.txt" Content-Disposition: attachment; filename="noplt_attrib_patch.txt" Content-Transfer-Encoding: base64 X-Attachment-Id: f_ia8iru1t0 Content-length: 5556 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