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[binutils-gdb] New gold linker option -z,text-unlikely-segment.
- From: Sriraman Tallam <tmsriram at sourceware dot org>
- To: bfd-cvs at sourceware dot org
- Date: 20 Oct 2017 18:02:22 -0000
- Subject: [binutils-gdb] New gold linker option -z,text-unlikely-segment.
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=3b4190ccb31be262a5aac78238e6d659746f1f0f
commit 3b4190ccb31be262a5aac78238e6d659746f1f0f
Author: Sriraman Tallam <tmsriram@google.com>
Date: Fri Oct 20 11:00:28 2017 -0700
New gold linker option -z,text-unlikely-segment.
2017-10-04 Sriraman Tallam <tmsriram@google.com>
* options.h (-z,text_unlikely_segment): New option.
* layout.cc (Layout::layout): Create new output section
for .text.unlikely sections with the new option.
(Layout::segment_precedes): Check for the new option
when segment flags match.
* testsuite/text_unlikely_segment.cc: New test source.
* testsuite/text_unlikely_segment.sh: New test script.
* testsuite/Makefile.am (text_unlikely_segment): New test.
* testsuite/Makefile.in: Regenerate.
Diff:
---
gold/ChangeLog | 12 ++++++
gold/layout.cc | 75 ++++++++++++++++++++++-----------
gold/options.h | 5 +++
gold/testsuite/Makefile.am | 10 +++++
gold/testsuite/Makefile.in | 11 +++++
gold/testsuite/text_unlikely_segment.cc | 30 +++++++++++++
gold/testsuite/text_unlikely_segment.sh | 60 ++++++++++++++++++++++++++
7 files changed, 178 insertions(+), 25 deletions(-)
diff --git a/gold/ChangeLog b/gold/ChangeLog
index c12214b..ce989f5 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -1,3 +1,15 @@
+2017-10-04 Sriraman Tallam <tmsriram@google.com>
+
+ * options.h (-z,text_unlikely_segment): New option.
+ * layout.cc (Layout::layout): Create new output section
+ for .text.unlikely sections with the new option.
+ (Layout::segment_precedes): Check for the new option
+ when segment flags match.
+ * testsuite/text_unlikely_segment.cc: New test source.
+ * testsuite/text_unlikely_segment.sh: New test script.
+ * testsuite/Makefile.am (text_unlikely_segment): New test.
+ * testsuite/Makefile.in: Regenerate.
+
2017-10-19 Umesh Kalappa <ukalappa@cisco.com>
* arm.cc (Stub::do_fixed_endian_write):Far call stubs support for arm
diff --git a/gold/layout.cc b/gold/layout.cc
index 5f25fae..15c5434 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -1178,38 +1178,62 @@ Layout::layout(Sized_relobj_file<size, big_endian>* object, unsigned int shndx,
}
else
{
- // Plugins can choose to place one or more subsets of sections in
- // unique segments and this is done by mapping these section subsets
- // to unique output sections. Check if this section needs to be
- // remapped to a unique output section.
- Section_segment_map::iterator it
- = this->section_segment_map_.find(Const_section_id(object, shndx));
- if (it == this->section_segment_map_.end())
- {
- os = this->choose_output_section(object, name, sh_type,
- shdr.get_sh_flags(), true,
- ORDER_INVALID, false, false,
- true);
- }
- else
- {
- // We know the name of the output section, directly call
- // get_output_section here by-passing choose_output_section.
+ // All ".text.unlikely.*" sections can be moved to a unique
+ // segment with --text-unlikely-segment option.
+ bool text_unlikely_segment
+ = (parameters->options().text_unlikely_segment()
+ && is_prefix_of(".text.unlikely",
+ object->section_name(shndx).c_str()));
+ if (text_unlikely_segment)
+ {
elfcpp::Elf_Xword flags
= this->get_output_section_flags(shdr.get_sh_flags());
- const char* os_name = it->second->name;
Stringpool::Key name_key;
- os_name = this->namepool_.add(os_name, true, &name_key);
+ const char* os_name = this->namepool_.add(".text.unlikely", true,
+ &name_key);
os = this->get_output_section(os_name, name_key, sh_type, flags,
ORDER_INVALID, false);
- if (!os->is_unique_segment())
+ // Map this output section to a unique segment. This is done to
+ // separate "text" that is not likely to be executed from "text"
+ // that is likely executed.
+ os->set_is_unique_segment();
+ }
+ else
+ {
+ // Plugins can choose to place one or more subsets of sections in
+ // unique segments and this is done by mapping these section subsets
+ // to unique output sections. Check if this section needs to be
+ // remapped to a unique output section.
+ Section_segment_map::iterator it
+ = this->section_segment_map_.find(Const_section_id(object, shndx));
+ if (it == this->section_segment_map_.end())
{
- os->set_is_unique_segment();
- os->set_extra_segment_flags(it->second->flags);
- os->set_segment_alignment(it->second->align);
+ os = this->choose_output_section(object, name, sh_type,
+ shdr.get_sh_flags(), true,
+ ORDER_INVALID, false, false,
+ true);
}
- }
+ else
+ {
+ // We know the name of the output section, directly call
+ // get_output_section here by-passing choose_output_section.
+ elfcpp::Elf_Xword flags
+ = this->get_output_section_flags(shdr.get_sh_flags());
+
+ const char* os_name = it->second->name;
+ Stringpool::Key name_key;
+ os_name = this->namepool_.add(os_name, true, &name_key);
+ os = this->get_output_section(os_name, name_key, sh_type, flags,
+ ORDER_INVALID, false);
+ if (!os->is_unique_segment())
+ {
+ os->set_is_unique_segment();
+ os->set_extra_segment_flags(it->second->flags);
+ os->set_segment_alignment(it->second->align);
+ }
+ }
+ }
if (os == NULL)
return NULL;
}
@@ -3449,7 +3473,8 @@ Layout::segment_precedes(const Output_segment* seg1,
// here if plugins want unique segments for subsets of sections.
gold_assert(this->script_options_->saw_phdrs_clause()
|| parameters->options().any_section_start()
- || this->is_unique_segment_for_sections_specified());
+ || this->is_unique_segment_for_sections_specified()
+ || parameters->options().text_unlikely_segment());
return false;
}
diff --git a/gold/options.h b/gold/options.h
index 678ca82..2a43e8d 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -1492,6 +1492,11 @@ class General_options
DEFINE_bool_alias(textoff, text, options::DASH_Z, '\0',
N_("Permit relocations in read-only segments"),
NULL, true);
+ DEFINE_bool(text_unlikely_segment, options::DASH_Z, '\0', false,
+ N_("Move .text.unlikely sections to a separate segment."),
+ N_("Do not move .text.unlikely sections to a separate "
+ "segment."));
+
public:
typedef options::Dir_list Dir_list;
diff --git a/gold/testsuite/Makefile.am b/gold/testsuite/Makefile.am
index 8eca3d8..d9a0669 100644
--- a/gold/testsuite/Makefile.am
+++ b/gold/testsuite/Makefile.am
@@ -340,6 +340,16 @@ section_sorting_name: section_sorting_name.o gcctestdir/ld
section_sorting_name.stdout: section_sorting_name
$(TEST_NM) -n --synthetic section_sorting_name > section_sorting_name.stdout
+check_SCRIPTS += text_unlikely_segment.sh
+check_DATA += text_unlikely_segment_readelf.stdout
+MOSTLYCLEANFILES += text_unlikely_segment
+text_unlikely_segment.o: text_unlikely_segment.cc
+ $(CXXCOMPILE) -O0 -c -ffunction-sections -g -o $@ $<
+text_unlikely_segment: text_unlikely_segment.o gcctestdir/ld
+ $(CXXLINK) -Bgcctestdir/ -Wl,-z,text-unlikely-segment text_unlikely_segment.o
+text_unlikely_segment_readelf.stdout: text_unlikely_segment
+ $(TEST_READELF) -Wl $< >$@
+
check_PROGRAMS += icf_virtual_function_folding_test
MOSTLYCLEANFILES += icf_virtual_function_folding_test icf_virtual_function_folding_test.map
icf_virtual_function_folding_test.o: icf_virtual_function_folding_test.cc
diff --git a/gold/testsuite/Makefile.in b/gold/testsuite/Makefile.in
index 10f9493..b8db70d 100644
--- a/gold/testsuite/Makefile.in
+++ b/gold/testsuite/Makefile.in
@@ -87,6 +87,7 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__EXEEXT_2) $(am__EXEEXT_3) \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ final_layout.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_section_grouping.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ section_sorting_name.sh \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_unlikely_segment.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_preemptible_functions_test.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_string_merge_test.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_sht_rel_addend_test.sh \
@@ -114,6 +115,7 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__EXEEXT_2) $(am__EXEEXT_3) \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_section_grouping.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_section_no_grouping.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ section_sorting_name.stdout \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_unlikely_segment_readelf.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_preemptible_functions_test.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_string_merge_test.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_sht_rel_addend_test.stdout \
@@ -139,6 +141,7 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__EXEEXT_2) $(am__EXEEXT_3) \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_section_grouping \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_section_no_grouping \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ section_sorting_name \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ text_unlikely_segment \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_virtual_function_folding_test \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_virtual_function_folding_test.map \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ icf_preemptible_functions_test \
@@ -5148,6 +5151,8 @@ text_section_grouping.sh.log: text_section_grouping.sh
@p='text_section_grouping.sh'; $(am__check_pre) $(LOG_COMPILE) "$$tst" $(am__check_post)
section_sorting_name.sh.log: section_sorting_name.sh
@p='section_sorting_name.sh'; $(am__check_pre) $(LOG_COMPILE) "$$tst" $(am__check_post)
+text_unlikely_segment.sh.log: text_unlikely_segment.sh
+ @p='text_unlikely_segment.sh'; $(am__check_pre) $(LOG_COMPILE) "$$tst" $(am__check_post)
icf_preemptible_functions_test.sh.log: icf_preemptible_functions_test.sh
@p='icf_preemptible_functions_test.sh'; $(am__check_pre) $(LOG_COMPILE) "$$tst" $(am__check_post)
icf_string_merge_test.sh.log: icf_string_merge_test.sh
@@ -6015,6 +6020,12 @@ uninstall-am:
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,--sort-section=name section_sorting_name.o
@GCC_TRUE@@NATIVE_LINKER_TRUE@section_sorting_name.stdout: section_sorting_name
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_NM) -n --synthetic section_sorting_name > section_sorting_name.stdout
+@GCC_TRUE@@NATIVE_LINKER_TRUE@text_unlikely_segment.o: text_unlikely_segment.cc
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXCOMPILE) -O0 -c -ffunction-sections -g -o $@ $<
+@GCC_TRUE@@NATIVE_LINKER_TRUE@text_unlikely_segment: text_unlikely_segment.o gcctestdir/ld
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,-z,text-unlikely-segment text_unlikely_segment.o
+@GCC_TRUE@@NATIVE_LINKER_TRUE@text_unlikely_segment_readelf.stdout: text_unlikely_segment
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_READELF) -Wl $< >$@
@GCC_TRUE@@NATIVE_LINKER_TRUE@icf_virtual_function_folding_test.o: icf_virtual_function_folding_test.cc
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXCOMPILE) -O0 -c -ffunction-sections -fPIE -g -o $@ $<
@GCC_TRUE@@NATIVE_LINKER_TRUE@icf_virtual_function_folding_test: icf_virtual_function_folding_test.o gcctestdir/ld
diff --git a/gold/testsuite/text_unlikely_segment.cc b/gold/testsuite/text_unlikely_segment.cc
new file mode 100644
index 0000000..f8e6dd7
--- /dev/null
+++ b/gold/testsuite/text_unlikely_segment.cc
@@ -0,0 +1,30 @@
+/* text_unlikey_segment.cc -- a test case for gold
+
+ Copyright (C) 2017 onwards Free Software Foundation, Inc.
+ Written by Sriraman Tallam <tmsriram@google.com>
+
+ 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. */
+
+__attribute__((section(".text.unlikely")))
+int foo(void) {
+ return 0;
+}
+
+int main(void) {
+ return 0;
+}
diff --git a/gold/testsuite/text_unlikely_segment.sh b/gold/testsuite/text_unlikely_segment.sh
new file mode 100755
index 0000000..b01fe6c
--- /dev/null
+++ b/gold/testsuite/text_unlikely_segment.sh
@@ -0,0 +1,60 @@
+#!/bin/sh
+
+# plugin_final_layout.sh -- test
+
+# Copyright (C) 2011-2017 Free Software Foundation, Inc.
+# Written by Sriraman Tallam <tmsriram@google.com>.
+
+# 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.
+
+# The goal of this program is to verify if -z,text-unlikely-segment works as
+# intended. File text_unlikely_segment.cc is part of this test.
+
+
+set -e
+
+# With readelf -l, an ELF Section to Segment mapping is printed as :
+##############################################
+# Section to Segment mapping:
+# Segment Sections...
+# ...
+# 0x .text.unlikely
+# ...
+##############################################
+# Check if .text.unlikely is the only section in the segment.
+check_unique_segment()
+{
+ awk "
+BEGIN { saw_section = 0; saw_unique = 0; }
+/$2/ { saw_section = 1; }
+/[ ]*0[0-9][ ]*$2[ ]*\$/ { saw_unique = 1; }
+END {
+ if (!saw_section)
+ {
+ printf \"Section $2 not seen in output\\n\";
+ exit 1;
+ }
+ else if (!saw_unique)
+ {
+ printf \"Unique segment not seen for: $2\\n\";
+ exit 1;
+ }
+ }" $1
+}
+
+check_unique_segment text_unlikely_segment_readelf.stdout ".text.unlikely"