From 1642b4b33783d70979dca379d57a0ce02559daec Mon Sep 17 00:00:00 2001 From: Sriraman Tallam Date: Tue, 13 May 2014 10:33:59 -0700 Subject: [PATCH] Optimizing accesses to Globals with -fpie -pie: With -pie and x86, the linker complains if it sees a PC-relative relocation to access a global as it expects a GOTPCREL relocation. This is really not necessary as the linker could use a copy relocation to get around it. This patch enables copy relocations with pie. Context: This is useful because currently the GCC compiler with option -fpie makes every extern global access go through the GOT. That is because the compiler cannot tell if a global will end up being defined in the executable or not and is conservative. This ends up hurting performance when the binary is linked as mostly static where most of the globals do end up being defined in the executable. By allowing copy relocs with fPIE, the compiler need not generate a GOTPCREL(GOT access) for any global access. It can safely assume that all globals will be defined in the executable and generate a PC-relative access instead. Gold can then create a copy reloc for only the undefined globals. --- gold/testsuite/pie_copyrelocs_shared_test.cc | 26 ++++++++++++++++ gold/testsuite/pie_copyrelocs_test.cc | 31 ++++++++++++++++++++ 2 files changed, 57 insertions(+) create mode 100644 gold/testsuite/pie_copyrelocs_shared_test.cc create mode 100644 gold/testsuite/pie_copyrelocs_test.cc diff --git a/gold/testsuite/pie_copyrelocs_shared_test.cc b/gold/testsuite/pie_copyrelocs_shared_test.cc new file mode 100644 index 00000000000..85134175df9 --- /dev/null +++ b/gold/testsuite/pie_copyrelocs_shared_test.cc @@ -0,0 +1,26 @@ +// pie_copyrelocs_shared_test.cc -- a test case for gold, used +// by pie_copyrelocs_test + +// Copyright (C) 2014 Free Software Foundation, Inc. +// Written by Sriraman Tallam . + +// This file is part of gold. + +// This program is free software; you can redistribute it and/or modify +// it under the terms of the GNU General Public License as published by +// the Free Software Foundation; either version 3 of the License, or +// (at your option) any later version. + +// This program is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License +// along with this program; if not, write to the Free Software +// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, +// MA 02110-1301, USA. + + + +int glob_a = 128; diff --git a/gold/testsuite/pie_copyrelocs_test.cc b/gold/testsuite/pie_copyrelocs_test.cc new file mode 100644 index 00000000000..bebe89dc333 --- /dev/null +++ b/gold/testsuite/pie_copyrelocs_test.cc @@ -0,0 +1,31 @@ +// pie_coprelocs_test.cc -- a test case for gold + +// Copyright (C) 2014 Free Software Foundation, Inc. +// Written by Sriraman Tallam . + +// This file is part of gold. + +// This program is free software; you can redistribute it and/or modify +// it under the terms of the GNU General Public License as published by +// the Free Software Foundation; either version 3 of the License, or +// (at your option) any later version. + +// This program is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. + +// You should have received a copy of the GNU General Public License +// along with this program; if not, write to the Free Software +// Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, +// MA 02110-1301, USA. + +// Check if copy relocs are used to access globals below when -fpie is +// is not used to compile but -pie is used to link. + +extern int glob_a; + +int main () +{ + return glob_a - 128; +} -- 2.30.2