Gold patch to create separate output sections for certain text section prefixes
Sriraman Tallam via binutils
binutils@sourceware.org
Tue Feb 20 17:28:00 GMT 2018
Ping.
* layout.cc (Layout::default_section_order): Check for text section
prefixes.
(Layout::text_section_name_mapping): New static member.
(Layout::text_section_name_mapping_count): New static member.
(Layout::match_section_name): New static function.
(Layout::output_section_name): Check for text section prefixes.
* layout.h (Output_section_order::ORDER_TEXT_HOT): New enum value.
(Output_section_order::ORDER_TEXT_STARTUP): New enum value.
(Output_section_order::ORDER_TEXT_EXIT): New enum value.
(Output_section_order::ORDER_TEXT_UNLIKELY): New enum value.
(Layout::text_section_name_mapping): New static member.
(Layout::text_section_name_mapping_count): New static member.
(Layout::match_section_name): New static function.
* options.h (keep_text_section_prefix): New -z option.
* testsuite/Makefile.am (keep_text_section_prefix): New test.
* testsuite/Makefile.in: Regenerate.
* testsuite/keep_text_section_prefix.cc: New test source.
* testsuite/keep_text_section_prefix.sh: New test script.
On Thu, Feb 15, 2018 at 5:20 PM, Sriraman Tallam <tmsriram@google.com> wrote:
> Hi,
>
> This patch creates separate output sections for .text.hot,
> .text.startup, .text.exit and .text.unlikely and is controlled by
> -z,keep-text-section-prefix. With this feature, the PT_LOAD segment
> would look like this:
>
> Section to Segment mapping:
> Segment Sections...
> 00
> 01 .interp
> 02 .interp ... .rela.dyn .rela.plt .init .plt .text.hot .text
> .text.startup .text.exit .text.unlikely .fini .rodata .eh_frame
> .eh_frame_hdr ...
> ....
>
> This feature would be useful to:
>
> a) Map only a subset of the text sections to huge pages.
> b) m(un)lock a subset the text sections.
> c) Code layout verification.
>
> I added -z,text-unlikely-segment here:
> https://sourceware.org/ml/binutils/2017-10/msg00023.html for similar
> reasons.
>
> However, we found out that creating multiple executable ELF segments
> has other issues as some other tools like symbolizers make assumptions
> about ELF binaries having just one executable segment and this breaks
> them. We are looking at fixing these but an alternate approach gives
> us flexibility in deploying this.
>
> Thoughts? Patch attached.
>
> * layout.cc (Layout::default_section_order): Check for text section
> prefixes.
> (Layout::text_section_name_mapping): New static member.
> (Layout::text_section_name_mapping_count): New static member.
> (Layout::match_section_name): New static function.
> (Layout::output_section_name): Check for text section prefixes.
> * layout.h (Output_section_order::ORDER_TEXT_HOT): New enum value.
> (Output_section_order::ORDER_TEXT_STARTUP): New enum value.
> (Output_section_order::ORDER_TEXT_EXIT): New enum value.
> (Output_section_order::ORDER_TEXT_UNLIKELY): New enum value.
> (Layout::text_section_name_mapping): New static member.
> (Layout::text_section_name_mapping_count): New static member.
> (Layout::match_section_name): New static function.
> * options.h (keep_text_section_prefix): New -z option.
> * testsuite/Makefile.am (keep_text_section_prefix): New test.
> * testsuite/Makefile.in: Regenerate.
> * testsuite/keep_text_section_prefix.cc: New test source.
> * testsuite/keep_text_section_prefix.sh: New test script.
>
> Thanks
> Sri
-------------- next part --------------
* layout.cc (Layout::default_section_order): Check for text section
prefixes.
(Layout::text_section_name_mapping): New static member.
(Layout::text_section_name_mapping_count): New static member.
(Layout::match_section_name): New static function.
(Layout::output_section_name): Check for text section prefixes.
* layout.h (Output_section_order::ORDER_TEXT_HOT): New enum value.
(Output_section_order::ORDER_TEXT_STARTUP): New enum value.
(Output_section_order::ORDER_TEXT_EXIT): New enum value.
(Output_section_order::ORDER_TEXT_UNLIKELY): New enum value.
(Layout::text_section_name_mapping): New static member.
(Layout::text_section_name_mapping_count): New static member.
(Layout::match_section_name): New static function.
* options.h (keep_text_section_prefix): New -z option.
* testsuite/Makefile.am (keep_text_section_prefix): New test.
* testsuite/Makefile.in: Regenerate.
* testsuite/keep_text_section_prefix.cc: New test source.
* testsuite/keep_text_section_prefix.sh: New test script.
diff --git a/gold/layout.cc b/gold/layout.cc
index 0ec7278a4a..36fd6fde20 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -1905,6 +1905,19 @@ Layout::default_section_order(Output_section* os, bool is_relro_local)
return ORDER_INIT;
else if (strcmp(os->name(), ".fini") == 0)
return ORDER_FINI;
+ else if (parameters->options().keep_text_section_prefix())
+ {
+ // -z,keep-text-section-prefix introduces additional
+ // output sections.
+ if (strcmp(os->name(), ".text.hot") == 0)
+ return ORDER_TEXT_HOT;
+ else if (strcmp(os->name(), ".text.startup") == 0)
+ return ORDER_TEXT_STARTUP;
+ else if (strcmp(os->name(), ".text.exit") == 0)
+ return ORDER_TEXT_EXIT;
+ else if (strcmp(os->name(), ".text.unlikely") == 0)
+ return ORDER_TEXT_UNLIKELY;
+ }
}
return is_execinstr ? ORDER_TEXT : ORDER_READONLY;
}
@@ -5134,6 +5147,20 @@ const Layout::Section_name_mapping Layout::section_name_mapping[] =
MAPPING_INIT(".ARM.exidx", ".ARM.exidx"),
MAPPING_INIT(".gnu.linkonce.armexidx.", ".ARM.exidx"),
};
+
+// Mapping for ".text" section prefixes with -z,keep-text-section-prefix.
+const Layout::Section_name_mapping Layout::text_section_name_mapping[] =
+{
+ MAPPING_INIT(".text.hot.", ".text.hot"),
+ MAPPING_INIT_EXACT(".text.hot", ".text.hot"),
+ MAPPING_INIT(".text.unlikely.", ".text.unlikely"),
+ MAPPING_INIT_EXACT(".text.unlikely", ".text.unlikely"),
+ MAPPING_INIT(".text.startup.", ".text.startup"),
+ MAPPING_INIT_EXACT(".text.startup", ".text.startup"),
+ MAPPING_INIT(".text.exit.", ".text.exit"),
+ MAPPING_INIT_EXACT(".text.exit", ".text.exit"),
+ MAPPING_INIT(".text.", ".text"),
+};
#undef MAPPING_INIT
#undef MAPPING_INIT_EXACT
@@ -5141,6 +5168,39 @@ const int Layout::section_name_mapping_count =
(sizeof(Layout::section_name_mapping)
/ sizeof(Layout::section_name_mapping[0]));
+const int Layout::text_section_name_mapping_count =
+ (sizeof(Layout::text_section_name_mapping)
+ / sizeof(Layout::text_section_name_mapping[0]));
+
+// Find section name NAME in PSNM and return the mapped name if found
+// with the length set in PLEN.
+const char *
+Layout::match_section_name(const Layout::Section_name_mapping* psnm,
+ const int count,
+ const char* name, size_t* plen)
+{
+ for (int i = 0; i < count; ++i, ++psnm)
+ {
+ if (psnm->fromlen > 0)
+ {
+ if (strncmp(name, psnm->from, psnm->fromlen) == 0)
+ {
+ *plen = psnm->tolen;
+ return psnm->to;
+ }
+ }
+ else
+ {
+ if (strcmp(name, psnm->from) == 0)
+ {
+ *plen = psnm->tolen;
+ return psnm->to;
+ }
+ }
+ }
+ return NULL;
+}
+
// Choose the output section name to use given an input section name.
// Set *PLEN to the length of the name. *PLEN is initialized to the
// length of NAME.
@@ -5184,27 +5244,21 @@ Layout::output_section_name(const Relobj* relobj, const char* name,
// not found in the table, we simply use it as the output section
// name.
- const Section_name_mapping* psnm = section_name_mapping;
- for (int i = 0; i < section_name_mapping_count; ++i, ++psnm)
+ if (parameters->options().keep_text_section_prefix()
+ && is_prefix_of(".text", name))
{
- if (psnm->fromlen > 0)
- {
- if (strncmp(name, psnm->from, psnm->fromlen) == 0)
- {
- *plen = psnm->tolen;
- return psnm->to;
- }
- }
- else
- {
- if (strcmp(name, psnm->from) == 0)
- {
- *plen = psnm->tolen;
- return psnm->to;
- }
- }
+ const char* match = match_section_name(text_section_name_mapping,
+ text_section_name_mapping_count,
+ name, plen);
+ if (match != NULL)
+ return match;
}
+ const char* match = match_section_name(section_name_mapping,
+ section_name_mapping_count, name, plen);
+ if (match != NULL)
+ return match;
+
// As an additional complication, .ctors sections are output in
// either .ctors or .init_array sections, and .dtors sections are
// output in either .dtors or .fini_array sections.
diff --git a/gold/layout.h b/gold/layout.h
index bbdc1622f6..0c34d3db19 100644
--- a/gold/layout.h
+++ b/gold/layout.h
@@ -422,9 +422,21 @@ enum Output_section_order
// The PLT.
ORDER_PLT,
+ // The hot text sections, prefixed by .text.hot.
+ ORDER_TEXT_HOT,
+
// The regular text sections.
ORDER_TEXT,
+ // The startup text sections, prefixed by .text.startup.
+ ORDER_TEXT_STARTUP,
+
+ // The startup text sections, prefixed by .text.startup.
+ ORDER_TEXT_EXIT,
+
+ // The unlikely text sections, prefixed by .text.unlikely.
+ ORDER_TEXT_UNLIKELY,
+
// The .fini section.
ORDER_FINI,
@@ -1015,6 +1027,14 @@ class Layout
};
static const Section_name_mapping section_name_mapping[];
static const int section_name_mapping_count;
+ static const Section_name_mapping text_section_name_mapping[];
+ static const int text_section_name_mapping_count;
+
+ // Find section name NAME in map and return the mapped name if found
+ // with the length set in PLEN.
+ static const char* match_section_name(const Section_name_mapping* map,
+ const int count, const char* name,
+ size_t* plen);
// During a relocatable link, a list of group sections and
// signatures.
diff --git a/gold/options.h b/gold/options.h
index b39d5ff7ba..1853f2e65f 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -1496,6 +1496,10 @@ class General_options
N_("Move .text.unlikely sections to a separate segment."),
N_("Do not move .text.unlikely sections to a separate "
"segment."));
+ DEFINE_bool(keep_text_section_prefix, options::DASH_Z, '\0', false,
+ N_("Keep .text.hot, .text.startup, .text.exit and .text.unlikely "
+ "as separate sections in the final binary."),
+ N_("Merge all .text.* prefix sections (default)."));
public:
diff --git a/gold/testsuite/Makefile.am b/gold/testsuite/Makefile.am
index 16cae8004c..34fe4bd698 100644
--- a/gold/testsuite/Makefile.am
+++ b/gold/testsuite/Makefile.am
@@ -354,6 +354,18 @@ text_unlikely_segment: text_unlikely_segment.o gcctestdir/ld
text_unlikely_segment_readelf.stdout: text_unlikely_segment
$(TEST_READELF) -Wl $< >$@
+check_SCRIPTS += keep_text_section_prefix.sh
+check_DATA += keep_text_section_prefix_readelf.stdout keep_text_section_prefix_nm.stdout
+MOSTLYCLEANFILES += keep_text_section_prefix
+keep_text_section_prefix.o: keep_text_section_prefix.cc
+ $(CXXCOMPILE) -O0 -c -ffunction-sections -g -o $@ $<
+keep_text_section_prefix: keep_text_section_prefix.o gcctestdir/ld
+ $(CXXLINK) -Bgcctestdir/ -Wl,-z,keep-text-section-prefix keep_text_section_prefix.o
+keep_text_section_prefix_readelf.stdout: keep_text_section_prefix
+ $(TEST_READELF) -Wl $< >$@
+keep_text_section_prefix_nm.stdout: keep_text_section_prefix
+ $(TEST_NM) -n $< >$@
+
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/keep_text_section_prefix.cc b/gold/testsuite/keep_text_section_prefix.cc
index e69de29bb2..1395d4c20b 100644
--- a/gold/testsuite/keep_text_section_prefix.cc
+++ b/gold/testsuite/keep_text_section_prefix.cc
@@ -0,0 +1,52 @@
+/* keep_text_section_prefix.cc -- a test case for gold
+
+ Copyright (C) 2018 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. */
+
+extern "C" {
+__attribute__((section(".text.unlikely.foo")))
+int unlikely_foo(void) {
+ return 0;
+}
+
+__attribute__((section(".text.hot.foo")))
+int hot_foo(void) {
+ return 0;
+}
+
+__attribute__((section(".text.startup.foo")))
+int startup_foo(void) {
+ return 0;
+}
+
+__attribute__((section(".text.exit.foo")))
+int exit_foo(void) {
+ return 0;
+}
+
+__attribute__((section(".text.foo")))
+int regular_foo(void) {
+ return 0;
+}
+
+int main(void) {
+ return 0;
+}
+}
diff --git a/gold/testsuite/keep_text_section_prefix.sh b/gold/testsuite/keep_text_section_prefix.sh
index e69de29bb2..44a2b47494 100755
--- a/gold/testsuite/keep_text_section_prefix.sh
+++ b/gold/testsuite/keep_text_section_prefix.sh
@@ -0,0 +1,77 @@
+#!/bin/sh
+
+# keep_text_section_prefix.sh -- test
+
+# Copyright (C) 2018 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 .text sections are separated
+# according to their prefix. .text.hot, .text.unlikely, .text.startup and
+# .text.exit must be separated in the final binary.
+
+set -e
+
+check()
+{
+ awk "
+BEGIN { saw1 = 0; saw2 = 0; err = 0; }
+/.*$2\$/ { saw1 = 1; }
+/.*$3\$/ {
+ saw2 = 1;
+ if (!saw1)
+ {
+ printf \"layout of $2 and $3 is not right\\n\";
+ err = 1;
+ exit 1;
+ }
+ }
+END {
+ if (!saw1 && !err)
+ {
+ printf \"did not see $2\\n\";
+ exit 1;
+ }
+ if (!saw2 && !err)
+ {
+ printf \"did not see $3\\n\";
+ exit 1;
+ }
+ }" $1
+}
+
+check_str()
+{
+ if ! grep -q "$2" "$1"
+ then
+ echo "Did not find expected output in $1:"
+ echo " $2"
+ echo ""
+ echo "Actual output below:"
+ cat "$1"
+ exit 1
+ fi
+}
+
+check_str keep_text_section_prefix_readelf.stdout ".text.hot .text .text.startup .text.exit .text.unlikely"
+
+check keep_text_section_prefix_nm.stdout "hot_foo" "regular_foo"
+check keep_text_section_prefix_nm.stdout "regular_foo" "startup_foo"
+check keep_text_section_prefix_nm.stdout "startup_foo" "exit_foo"
+check keep_text_section_prefix_nm.stdout "exit_foo" "unlikely_foo"
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