From patchwork Thu May 21 21:31:16 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sriraman Tallam X-Patchwork-Id: 475230 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org 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 ozlabs.org (Postfix) with ESMTPS id 7DC7C140D60 for ; Fri, 22 May 2015 07:31:30 +1000 (AEST) Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=gcc.gnu.org header.i=@gcc.gnu.org header.b=yOrJw8L5; dkim-atps=neutral DomainKey-Signature: a=rsa-sha1; c=nofws; d=gcc.gnu.org; h=list-id :list-unsubscribe:list-archive:list-post:list-help:sender :mime-version:in-reply-to:references:date:message-id:subject :from:to:cc:content-type; q=dns; s=default; b=TWVSps7FvFNaz5t+wT NKEQp9qjb3R577vRbNZbcdsvK4zkeK8s00kLn9KV6lBK9yQrSoMWpPVQT2xWaBXJ YDrZ938iGjWmExTgcQU0pbTjz5+Zj0c9daVV2H0Rf9oaYLFAIO0GjQUHQ6npQGD/ 6Yv1fPahsE0JnWvcM0s46+BSY= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=gcc.gnu.org; h=list-id :list-unsubscribe:list-archive:list-post:list-help:sender :mime-version:in-reply-to:references:date:message-id:subject :from:to:cc:content-type; s=default; bh=veeVlj0QenhKirsYMOvmi0ws nzQ=; b=yOrJw8L5W3B6CqAPNNMix9ALzd52bHcfiSjLl4uHHF2Kfo4S5ZFfMhV2 V73BveFKr9gsvup/i8suta1+wF/EqmByCotDHg8fE2JII8UhoTM43qGZiVzPstfA LBS6dbt075JOlZE1BSVTPWepxLTvx1jLymOZhhFYiA2tSVpNZdQ= Received: (qmail 79828 invoked by alias); 21 May 2015 21:31:22 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Delivered-To: mailing list gcc-patches@gcc.gnu.org Received: (qmail 79818 invoked by uid 89); 21 May 2015 21:31:21 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=1.4 required=5.0 tests=AWL, BAYES_95, 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-f51.google.com Received: from mail-vn0-f51.google.com (HELO mail-vn0-f51.google.com) (209.85.216.51) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Thu, 21 May 2015 21:31:19 +0000 Received: by vnbf129 with SMTP id f129so9098vnb.10 for ; Thu, 21 May 2015 14:31:17 -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=AdWi81Ue/wLVYPPMO6tc36ehEqS3LMaK2wst7GYA7Z4=; b=f/ngwghiiLOf8+cH4zol+CNeWD1mpwjpJabe4AZvYSS6oy1Z9LlxHf5sfLJpzmEm5R Vr3lXDOL6au1CYsl3y4d7hRj6qwO9rV1zHZYN8eLR/zev3wfVILx/eLdwjGMx1S6OYtp rvmTQvcD8tBvumzuHwYZL7ciQfT4MJc0hc+BA6i4YFHQVP4Gad081S9UNqCbGbsU2GIF YIFRxsNj/5cJW3FVcTLk99h2EHYPGafrs9xpQXimkdq3QqHjerKIVaMlv3YBL7G6KPJ3 8IKupwW9SuQ5siRA5O+UMygpd77u6x+AyydgkRTTRBlnbxs/xMnrkrFeu9OVNv3troKS s91A== X-Gm-Message-State: ALoCoQmBn9nDuDgsQY2KEuEEDURKHWvDUdlakDsPONvxp97yDwiwkbI+Sj+US5Kl6VtRGmvsO3xb MIME-Version: 1.0 X-Received: by 10.52.89.174 with SMTP id bp14mr4137503vdb.58.1432243877091; Thu, 21 May 2015 14:31:17 -0700 (PDT) Received: by 10.52.229.196 with HTTP; Thu, 21 May 2015 14:31:16 -0700 (PDT) In-Reply-To: References: Date: Thu, 21 May 2015 14:31:16 -0700 Message-ID: Subject: Re: [RFC][PATCH][X86_64] Eliminate PLT stubs for specified external functions via -fno-plt= From: Sriraman Tallam To: "H.J. Lu" , Michael Matz , Jan Hubicka , amonakov@ispras.ru Cc: David Li , GCC Patches , Richard Biener X-IsSubscribed: yes On Thu, May 21, 2015 at 2:12 PM, Sriraman Tallam wrote: > On Sun, May 10, 2015 at 10:01 AM, Sriraman Tallam wrote: >> >> On Sun, May 10, 2015, 8:19 AM H.J. Lu wrote: >> >> On Sat, May 9, 2015 at 9:34 AM, H.J. Lu wrote: >>> On Mon, May 4, 2015 at 7:45 AM, Michael Matz wrote: >>>> Hi, >>>> >>>> On Thu, 30 Apr 2015, Sriraman Tallam wrote: >>>> >>>>> We noticed that one of our benchmarks sped-up by ~1% when we eliminated >>>>> PLT stubs for some of the hot external library functions like memcmp, >>>>> pow. The win was from better icache and itlb performance. The main >>>>> reason was that the PLT stubs had no spatial locality with the >>>>> call-sites. I have started looking at ways to tell the compiler to >>>>> eliminate PLT stubs (in-effect inline them) for specified external >>>>> functions, for x86_64. I have a proposal and a patch and I would like to >>>>> hear what you think. >>>>> >>>>> This comes with caveats. This cannot be generally done for all >>>>> functions marked extern as it is impossible for the compiler to say if a >>>>> function is "truly extern" (defined in a shared library). If a function >>>>> is not truly extern(ends up defined in the final executable), then >>>>> calling it indirectly is a performance penalty as it could have been a >>>>> direct call. >>>> >>>> This can be fixed by Alans idea. >>>> >>>>> Further, the newly created GOT entries are fixed up at >>>>> start-up and do not get lazily bound. >>>> >>>> And this can be fixed by some enhancements in the linker and dynamic >>>> linker. The idea is to still generate a PLT stub and make its GOT entry >>>> point to it initially (like a normal got.plt slot). Then the first >>>> indirect call will use the address of PLT entry (starting lazy >>>> resolution) >>>> and update the GOT slot with the real address, so further indirect calls >>>> will directly go to the function. >>>> >>>> This requires a new asm marker (and hence new reloc) as normally if >>>> there's a GOT slot it's filled by the real symbols address, unlike if >>>> there's only a got.plt slot. E.g. a >>>> >>>> call *foo@GOTPLT(%rip) >>>> >>>> would generate a GOT slot (and fill its address into above call insn), >>>> but >>>> generate a JUMP_SLOT reloc in the final executable, not a GLOB_DAT one. >>>> >>> >>> I added the "relax" prefix support to x86 assembler on users/hjl/relax >>> branch >>> >>> at >>> >>> https://sourceware.org/git/?p=binutils-gdb.git;a=summary >>> >>> [hjl@gnu-tools-1 relax-3]$ cat r.S >>> .text >>> relax jmp foo >>> relax call foo >>> relax jmp foo@plt >>> relax call foo@plt >>> [hjl@gnu-tools-1 relax-3]$ ./as -o r.o r.S >>> [hjl@gnu-tools-1 relax-3]$ ./objdump -drw r.o >>> >>> r.o: file format elf64-x86-64 >>> >>> >>> Disassembly of section .text: >>> >>> 0000000000000000 <.text>: >>> 0: 66 e9 00 00 00 00 data16 jmpq 0x6 2: R_X86_64_RELAX_PC32 foo-0x4 >>> 6: 66 e8 00 00 00 00 data16 callq 0xc 8: R_X86_64_RELAX_PC32 >>> foo-0x4 >>> c: 66 e9 00 00 00 00 data16 jmpq 0x12 e: >>> R_X86_64_RELAX_PLT32foo-0x4 >>> 12: 66 e8 00 00 00 00 data16 callq 0x18 14: >>> R_X86_64_RELAX_PLT32foo-0x4 >>> [hjl@gnu-tools-1 relax-3]$ >>> >>> Right now, the relax relocations are treated as PC32/PLT32 relocations. >>> I am working on linker support. >>> >> >> I implemented the linker support for x86-64: >> >> 00000000
: >> 0: 48 83 ec 08 sub $0x8,%rsp >> 4: e8 00 00 00 00 callq 9 5: R_X86_64_PC32 plt-0x4 >> 9: e8 00 00 00 00 callq e a: R_X86_64_PLT32 plt-0x4 >> e: e8 00 00 00 00 callq 13 f: R_X86_64_PC32 bar-0x4 >> 13: 66 e8 00 00 00 00 data16 callq 19 15: >> R_X86_64_RELAX_PC32 bar-0x4 >> 19: 66 e8 00 00 00 00 data16 callq 1f 1b: >> R_X86_64_RELAX_PLT32 bar-0x4 >> 1f: 66 e8 00 00 00 00 data16 callq 25 21: >> R_X86_64_RELAX_PC32 foo-0x4 >> 25: 66 e8 00 00 00 00 data16 callq 2b 27: >> R_X86_64_RELAX_PLT32 foo-0x4 >> 2b: 31 c0 xor %eax,%eax >> 2d: 48 83 c4 08 add $0x8,%rsp >> 31: c3 retq >> >> 00400460
: >> 400460: 48 83 ec 08 sub $0x8,%rsp >> 400464: e8 d7 ff ff ff callq 400440 >> 400469: e8 d2 ff ff ff callq 400440 >> 40046e: e8 ad ff ff ff callq 400420 >> 400473: ff 15 ff 03 20 00 callq *0x2003ff(%rip) # 600878 >> <_DYNAMIC+0xf8> >> 400479: ff 15 f9 03 20 00 callq *0x2003f9(%rip) # 600878 >> <_DYNAMIC+0xf8> >> 40047f: 66 e8 f3 00 00 00 data16 callq 400578 >> 400485: 66 e8 ed 00 00 00 data16 callq 400578 >> 40048b: 31 c0 xor %eax,%eax >> 40048d: 48 83 c4 08 add $0x8,%rsp >> 400491: c3 retq >> >> Sriraman, can you give it a try? > > > I like HJ's proposal here and it is important that the linker fixes > unnecessary indirect calls to direct ones. > > However, independently I think my original proposal is still useful > and I want to pitch it again for the following reasons. > > AFAIU, Alexander Monakov's -fno-plt does not solve the following: > > * Does not do anything for non-PIC code. The compiler does not > generate a @PLT call but the linker will route all external calls via > PLT. We noticed a problem with non-PIC executables where the PLT > stubs were causing too many icache misses and are interested in a > solution for this. > * Aggressively uses indirect calls even if the final symbol is not > truly external. This needs HJ's linker patch to fix unnecessary > indirect calls to direct calls. > > 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. > > I am reattaching the patch. I also want to add that my proposal with -fno-plt= does not take away anything from the newly added -fno-plt option or the linker patch HJ proposed. It is orthogonal and lets the user decide the subset of external functions for which PLT must be avoided. Thanks Sri > > Thanks > Sri > > >> >> Thanks! Will do! >> >> Sri >> >> -- >> H.J. >> >> * common.opt (-fno-plt=): New option. * config/i386/i386.c (avoid_plt_to_call): New function. (ix86_output_call_insn): Check if PLT needs to be avoided and call or jump indirectly if true. * opts-global.c (htab_str_eq): New function. (avoid_plt_fnsymbol_names_tab): New htab. (handle_common_deferred_options): Handle -fno-plt= Index: common.opt =================================================================== --- common.opt (revision 222892) +++ common.opt (working copy) @@ -1087,6 +1087,11 @@ fdbg-cnt= Common RejectNegative Joined Var(common_deferred_options) Defer -fdbg-cnt=:[,:,...] Set the debug counter limit. +fno-plt= +Common RejectNegative Joined Var(common_deferred_options) Defer +-fno-plt= Avoid going through the PLT when calling the specified function. +Allow multiple instances of this option with different function names. + fdebug-prefix-map= Common Joined RejectNegative Var(common_deferred_options) Defer Map one directory name to another in debug information Index: config/i386/i386.c =================================================================== --- config/i386/i386.c (revision 222892) +++ config/i386/i386.c (working copy) @@ -25282,6 +25282,25 @@ ix86_expand_call (rtx retval, rtx fnaddr, rtx call return call; } +extern htab_t avoid_plt_fnsymbol_names_tab; +/* If the function referenced by call_op is to a external function + and calls via PLT must be avoided as specified by -fno-plt=, then + return true. */ + +static int +avoid_plt_to_call(rtx call_op) +{ + const char *name; + if (GET_CODE (call_op) != SYMBOL_REF + || SYMBOL_REF_LOCAL_P (call_op) + || avoid_plt_fnsymbol_names_tab == NULL) + return 0; + name = XSTR (call_op, 0); + if (htab_find_slot (avoid_plt_fnsymbol_names_tab, name, NO_INSERT) != NULL) + return 1; + return 0; +} + /* Output the assembly for a call instruction. */ const char * @@ -25294,7 +25313,12 @@ ix86_output_call_insn (rtx insn, rtx call_op) if (SIBLING_CALL_P (insn)) { if (direct_p) - xasm = "jmp\t%P0"; + { + if (avoid_plt_to_call (call_op)) + xasm = "jmp\t*%p0@GOTPCREL(%%rip)"; + else + xasm = "jmp\t%P0"; + } /* SEH epilogue detection requires the indirect branch case to include REX.W. */ else if (TARGET_SEH) @@ -25346,9 +25370,15 @@ ix86_output_call_insn (rtx insn, rtx call_op) } if (direct_p) - xasm = "call\t%P0"; + { + if (avoid_plt_to_call (call_op)) + xasm = "call\t*%p0@GOTPCREL(%%rip)"; + else + xasm = "call\t%P0"; + } else xasm = "call\t%A0"; + output_asm_insn (xasm, &call_op); Index: opts-global.c =================================================================== --- opts-global.c (revision 222892) +++ opts-global.c (working copy) @@ -47,6 +47,7 @@ along with GCC; see the file COPYING3. If not see #include "xregex.h" #include "attribs.h" #include "stringpool.h" +#include "hash-table.h" typedef const char *const_char_p; /* For DEF_VEC_P. */ @@ -420,6 +421,17 @@ decode_options (struct gcc_options *opts, struct g finish_options (opts, opts_set, loc); } +/* Helper function for the hash table that compares the + existing entry (S1) with the given string (S2). */ + +static int +htab_str_eq (const void *s1, const void *s2) +{ + return !strcmp ((const char *)s1, (const char *) s2); +} + +htab_t avoid_plt_fnsymbol_names_tab = NULL; + /* Process common options that have been deferred until after the handlers have been called for all options. */ @@ -539,6 +551,15 @@ handle_common_deferred_options (void) stack_limit_rtx = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (opt->arg)); break; + case OPT_fno_plt_: + void **slot; + if (avoid_plt_fnsymbol_names_tab == NULL) + avoid_plt_fnsymbol_names_tab = htab_create (10, htab_hash_string, + htab_str_eq, NULL); + slot = htab_find_slot (avoid_plt_fnsymbol_names_tab, opt->arg, INSERT); + *slot = (void *)opt->arg; + break; + default: gcc_unreachable (); }