[PATCH] add section alignment/size hooks to gold plugin interface, revised

[Than McIntosh <thanm at google dot com>]

Second attempt at posting revised patch (first email was blocked by
SpamAssassin).

Hi Cary,

I've incorporated all of your suggestions, revised patch attached.
Thanks for your feedback.

Regards,

Than

include/
2016-02-26  Than McIntosh <thanm@google.com>

        * plugin-api.h: Add new hooks to the plugin transfer vector to
        to support querying section alignment and section size.
        (ld_plugin_get_input_section_alignment): New hook.
        (ld_plugin_get_input_section_size): New hook.
        (ld_plugin_tag): Add LDPT_GET_INPUT_SECTION_ALIGNMENT
          and LDPT_GET_INPUT_SECTION_SIZE.
        (ld_plugin_tv): Add tv_get_input_section_alignment and
          tv_get_input_section_size.

gold/
2016-02-26  Than McIntosh  <thanm@google.com>

        * plugin.cc (Plugin::load): Include hooks for get_input_section_size
        and get_input_section_alignment in transfer vector.
        (get_input_section_alignment): New function.
        (get_input_section_size): New function.
        * testsuite/Makefile.am: Add plugin_layout_with_alignment.sh test.
        * testsuite/Makefile.in: [Regenerate.]
        * testsuite/plugin_section_alignment.cc: New test file.
        * testsuite/plugin_layout_with_alignment.cc: New test file.
        * testsuite/plugin_layout_with_alignment.sh: New test file.

---

diff --git a/gold/plugin.cc b/gold/plugin.cc
index c01e4cd..a0ef240 100644
--- a/gold/plugin.cc
+++ b/gold/plugin.cc
@@ -155,6 +155,15 @@ unique_segment_for_sections(const char* segment_name,
     uint64_t align,
     const struct ld_plugin_section *section_list,
     unsigned int num_sections);
+
+static enum ld_plugin_status
+get_input_section_alignment(const struct ld_plugin_section section,
+                            unsigned int* addralign);
+
+static enum ld_plugin_status
+get_input_section_size(const struct ld_plugin_section section,
+                       uint64_t* secsize);
+
 };

 #endif // ENABLE_PLUGINS
@@ -199,7 +208,7 @@ Plugin::load()
   sscanf(ver, "%d.%d", &major, &minor);

   // Allocate and populate a transfer vector.
-  const int tv_fixed_size = 26;
+  const int tv_fixed_size = 28;

   int tv_size = this->args_.size() + tv_fixed_size;
   ld_plugin_tv* tv = new ld_plugin_tv[tv_size];
@@ -322,6 +331,14 @@ Plugin::load()
   tv[i].tv_u.tv_unique_segment_for_sections = unique_segment_for_sections;

   ++i;
+  tv[i].tv_tag = LDPT_GET_INPUT_SECTION_ALIGNMENT;
+  tv[i].tv_u.tv_get_input_section_alignment = get_input_section_alignment;
+
+  ++i;
+  tv[i].tv_tag = LDPT_GET_INPUT_SECTION_SIZE;
+  tv[i].tv_u.tv_get_input_section_size = get_input_section_size;
+
+  ++i;
   tv[i].tv_tag = LDPT_NULL;
   tv[i].tv_u.tv_val = 0;

@@ -1703,6 +1720,53 @@ get_input_section_contents(const struct
ld_plugin_section section,
   return LDPS_OK;
 }

+// Get the alignment of the specified section in the object corresponding
+// to the handle.  This plugin interface can only be called in the
+// claim_file handler of the plugin.
+
+static enum ld_plugin_status
+get_input_section_alignment(const struct ld_plugin_section section,
+                            unsigned int* addralign)
+{
+  gold_assert(parameters->options().has_plugins());
+
+  if (!parameters->options().plugins()->in_claim_file_handler())
+    return LDPS_ERR;
+
+  Object* obj
+    = parameters->options().plugins()->get_elf_object(section.handle);
+
+  if (obj == NULL)
+    return LDPS_BAD_HANDLE;
+
+  *addralign = obj->section_addralign(section.shndx);
+  return LDPS_OK;
+}
+
+// Get the size of the specified section in the object corresponding
+// to the handle.  This plugin interface can only be called in the
+// claim_file handler of the plugin.
+
+static enum ld_plugin_status
+get_input_section_size(const struct ld_plugin_section section,
+                       uint64_t* secsize)
+{
+  gold_assert(parameters->options().has_plugins());
+
+  if (!parameters->options().plugins()->in_claim_file_handler())
+    return LDPS_ERR;
+
+  Object* obj
+    = parameters->options().plugins()->get_elf_object(section.handle);
+
+  if (obj == NULL)
+    return LDPS_BAD_HANDLE;
+
+  *secsize = obj->section_size(section.shndx);
+  return LDPS_OK;
+}
+
+
 // Specify the ordering of sections in the final layout. The sections are
 // specified as (handle,shndx) pairs in the two arrays in the order in
 // which they should appear in the final layout.
diff --git a/gold/testsuite/Makefile.am b/gold/testsuite/Makefile.am
index 32906db..34129f4 100644
--- a/gold/testsuite/Makefile.am
+++ b/gold/testsuite/Makefile.am
@@ -2085,6 +2085,21 @@ plugin_section_order.so: plugin_section_order.o
 plugin_section_order.o: plugin_section_order.c
  $(COMPILE) -O0 -c -fpic -o $@ $<

+check_SCRIPTS += plugin_layout_with_alignment.sh
+check_DATA += plugin_layout_with_alignment.stdout
+MOSTLYCLEANFILES += plugin_layout_with_alignment
+plugin_layout_with_alignment.o: plugin_layout_with_alignment.cc
+ $(CXXCOMPILE) -O0 -c -ffunction-sections  -fdata-sections -g -o $@ $<
+plugin_layout_with_alignment: plugin_layout_with_alignment.o
plugin_section_alignment.so gcctestdir/ld
+ $(CXXLINK) -Bgcctestdir/
-Wl,--plugin,"./plugin_section_alignment.so"
plugin_layout_with_alignment.o
+plugin_layout_with_alignment.stdout: plugin_layout_with_alignment
+ $(TEST_NM) -n --synthetic plugin_layout_with_alignment >
plugin_layout_with_alignment.stdout
+
+plugin_section_alignment.so: plugin_section_alignment.o
+ $(CXXLINK) -Bgcctestdir/ -shared plugin_section_alignment.o
+plugin_section_alignment.o: plugin_section_alignment.cc
+ $(CXXCOMPILE) -O0 -c -fpic -o $@ $<
+
 endif PLUGINS

 check_PROGRAMS += exclude_libs_test
diff --git a/gold/testsuite/plugin_layout_with_alignment.cc
b/gold/testsuite/plugin_layout_with_alignment.cc
new file mode 100644
index 0000000..0824d74
--- /dev/null
+++ b/gold/testsuite/plugin_layout_with_alignment.cc
@@ -0,0 +1,72 @@
+// plugin_layout_with_alignment.cc -- a test case for gold
+
+// Copyright (C) 2016 Free Software Foundation, Inc.
+// Written by Than McIntosh <thanm@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.
+
+// Verify that plugin interfaces for section size and alignment work
+// correctly, and that section ordering via plugins is working
+// for .bss/.rodata/.data sections.
+
+// --- Initialized .rodata items
+
+__attribute__ ((section(".rodata.v1_a2")))
+const short rodata_item1 = 101;
+
+__attribute__ ((section(".rodata.v2_a1")))
+const char rodata_item2 = 'a';
+
+__attribute__ ((section(".rodata.v3_a8")))
+const double rodata_item3 = 777.777;
+
+__attribute__ ((section(".rodata.v4_a1")))
+const char rodata_item4[7] = {'1', '2', '3', '4', '5', '6', '7'};
+
+// --- Initialized .data items
+
+__attribute__ ((section(".data.v1_a2")))
+short rwdata_item1 = 101;
+
+__attribute__ ((section(".data.v2_a1")))
+char rwdata_item2 = 'a';
+
+__attribute__ ((section(".data.v3_a8")))
+double rwdata_item3 = 'b';
+
+__attribute__ ((section(".data.v4_a1")))
+char rwdata_item4[3] = {'a', 'b', 'c'};
+
+// --- Uninitialized .data items
+
+__attribute__ ((section(".bss.v1_a2")))
+short bss_item1;
+
+__attribute__ ((section(".bss.v2_a1")))
+char bss_item2;
+
+__attribute__ ((section(".bss.v3_a8")))
+struct blah { union { double d; char c; } u; } bss_item3;
+
+__attribute__ ((section(".bss.v4_a1")))
+char bss_item4[3];
+
+int main ()
+{
+  return 0;
+}
diff --git a/gold/testsuite/plugin_layout_with_alignment.sh
b/gold/testsuite/plugin_layout_with_alignment.sh
new file mode 100755
index 0000000..c5f07ae
--- /dev/null
+++ b/gold/testsuite/plugin_layout_with_alignment.sh
@@ -0,0 +1,66 @@
+#!/bin/sh
+
+# plugin_layout_with_alignment.sh -- test
+
+# Copyright (C) 2016 Free Software Foundation, Inc.
+# Written by Than McIntosh <thanm@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 plugin alignment and size
+# interfaces and working correctly in combination with section ordering.
+# intended.  File plugin_layout_with_alignment.cc is in this test.
+
+
+set -e
+
+check()
+{
+    awk "
+BEGIN { saw1 = 0; saw2 = 0; saw3 = 0; saw4 = 0; counter = 1; err = 0;
ord = \"\"; }
+/.*$2\$/ { saw1 = counter; counter = counter + 1; ord = ord \" $2\";  }
+/.*$3\$/ { saw2 = counter; counter = counter + 1; ord = ord \" $3\";  }
+/.*$4\$/ { saw3 = counter; counter = counter + 1; ord = ord \" $4\";  }
+/.*$5\$/ { saw4 = counter; counter = counter + 1; ord = ord \" $5\";  }
+END {
+      if (!saw1) {
+  printf \"did not see $2\\n\";
+  exit 1;
+ }
+      if (!saw2) {
+  printf \"did not see $3\\n\";
+  exit 1;
+ }
+      if (!saw3) {
+  printf \"did not see $4\\n\";
+  exit 1;
+ }
+      if (!saw4) {
+  printf \"did not see $5\\n\";
+  exit 1;
+ }
+      if (saw1 != 1 || saw2 != 2 || saw3 != 3 || saw4 != 4) {
+  printf \"incorrect ordering:\\nwas:%s\\nshould have been: $2 $3 $4
$5\\n\", ord;
+  exit 1;
+ }
+    }" $1
+}
+
+check plugin_layout_with_alignment.stdout "bss_item3" "bss_item1"
"bss_item4" "bss_item2"
+check plugin_layout_with_alignment.stdout "rwdata_item2"
"rwdata_item4" "rwdata_item1" "rwdata_item3"
+check plugin_layout_with_alignment.stdout "rodata_item3"
"rodata_item1" "rodata_item2" "rodata_item4"
diff --git a/gold/testsuite/plugin_section_alignment.cc
b/gold/testsuite/plugin_section_alignment.cc
new file mode 100644
index 0000000..6f64bdc
--- /dev/null
+++ b/gold/testsuite/plugin_section_alignment.cc
@@ -0,0 +1,267 @@
+// plugin_section_alignment.cc -- plugins to test ordering with
{size,alignment}
+//
+// Copyright (C) 2016 Free Software Foundation, Inc.
+// Written by Than McIntosh <thanm@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.
+//
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <string>
+#include <vector>
+#include <algorithm>
+
+#include "plugin-api.h"
+
+static ld_plugin_get_input_section_count get_input_section_count = NULL;
+static ld_plugin_get_input_section_alignment
get_input_section_alignment = NULL;
+static ld_plugin_get_input_section_size get_input_section_size = NULL;
+static ld_plugin_get_input_section_name get_input_section_name = NULL;
+static ld_plugin_update_section_order update_section_order = NULL;
+static ld_plugin_allow_section_ordering allow_section_ordering = NULL;
+
+extern "C" {
+  enum ld_plugin_status onload(struct ld_plugin_tv *tv);
+  enum ld_plugin_status claim_file_hook(const struct
ld_plugin_input_file *file,
+                                        int *claimed);
+  enum ld_plugin_status all_symbols_read_hook(void);
+}
+
+typedef enum { FL_BSS, FL_DATA, FL_RODATA, FL_UNKNOWN } sec_flavor;
+
+inline static int is_prefix_of(const char *prefix, const char *str)
+{
+  return strncmp(prefix, str, strlen(prefix)) == 0;
+}
+
+inline static sec_flavor flavor_from_name(const char *secname)
+{
+  if (is_prefix_of(".data.v", secname)) {
+    return FL_DATA;
+  } else if (is_prefix_of(".bss.v", secname)) {
+    return FL_BSS;
+  } else if (is_prefix_of(".rodata.v", secname)) {
+    return FL_RODATA;
+  } else {
+    return FL_UNKNOWN;
+  }
+}
+
+struct SectionInfo {
+  ld_plugin_section plugin_section;
+  std::string name;
+  uint64_t size;
+  sec_flavor flavor;
+  unsigned align;
+
+  static bool SectionInfoLt(const SectionInfo &i1,
+                            const SectionInfo &i2)
+  {
+    if (i1.flavor != i2.flavor) {
+      return ((unsigned) i1.flavor) < ((unsigned) i2.flavor);
+    }
+    switch (i1.flavor) {
+      case FL_DATA:
+        // Sort data items by increasing alignment then increasing size
+        if (i1.align != i2.align) {
+          return ((unsigned) i1.align) < ((unsigned) i2.align);
+        }
+        if (i1.size != i2.size) {
+          return ((unsigned) i1.size) < ((unsigned) i2.size);
+        }
+        break;
+      case FL_BSS:
+        // Sort bss items by decreasing alignment then decreasing size
+        if (i1.align != i2.align) {
+          return ((unsigned) i2.align) < ((unsigned) i1.align);
+        }
+        if (i1.size != i2.size) {
+          return ((unsigned) i2.size) < ((unsigned) i1.size);
+        }
+        break;
+      case FL_RODATA:
+        // Sort rodata items by decreasing alignment then increasing size
+        if (i1.align != i2.align) {
+          return ((unsigned) i2.align) < ((unsigned) i1.align);
+        }
+        if (i1.size != i2.size) {
+          return ((unsigned) i1.size) < ((unsigned) i2.size);
+        }
+      default:
+        break;
+    }
+
+    // Break ties by name
+    return i1.name.compare(i2.name) < 0;
+  }
+
+};
+typedef std::vector<SectionInfo> section_info_vector;
+section_info_vector raw_sections;
+
+// Set to 1 for debugging output
+unsigned trace = 0;
+
+extern "C" {
+
+// Plugin entry point.
+enum ld_plugin_status onload(struct ld_plugin_tv *tv)
+{
+  struct ld_plugin_tv *entry;
+  for (entry = tv; entry->tv_tag != LDPT_NULL; ++entry)
+  {
+    switch (entry->tv_tag)
+    {
+      case LDPT_OPTION:
+        if (!strcmp(entry->tv_u.tv_string,"-trace")) {
+          fprintf(stderr, "enabling tracing\n");
+          trace += 1;
+        } else {
+          fprintf(stderr, "unknown plugin option %s", entry->tv_u.tv_string);
+        }
+        break;
+      case LDPT_REGISTER_CLAIM_FILE_HOOK:
+        assert((*entry->tv_u.tv_register_claim_file)(claim_file_hook) ==
+               LDPS_OK);
+        break;
+      case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK:
+        assert((*entry->tv_u.tv_register_all_symbols_read)(
+            all_symbols_read_hook) == LDPS_OK);
+        break;
+      case LDPT_GET_INPUT_SECTION_COUNT:
+        get_input_section_count = *entry->tv_u.tv_get_input_section_count;
+        break;
+      case LDPT_GET_INPUT_SECTION_NAME:
+        get_input_section_name = *entry->tv_u.tv_get_input_section_name;
+        break;
+      case LDPT_GET_INPUT_SECTION_ALIGNMENT:
+        get_input_section_alignment =
+            *entry->tv_u.tv_get_input_section_alignment;
+        break;
+      case LDPT_GET_INPUT_SECTION_SIZE:
+        get_input_section_size = *entry->tv_u.tv_get_input_section_size;
+        break;
+      case LDPT_UPDATE_SECTION_ORDER:
+        update_section_order = *entry->tv_u.tv_update_section_order;
+        break;
+      case LDPT_ALLOW_SECTION_ORDERING:
+        allow_section_ordering = *entry->tv_u.tv_allow_section_ordering;
+        break;
+      default:
+        break;
+    }
+  }
+
+  if (get_input_section_count == NULL || get_input_section_alignment == NULL ||
+      get_input_section_size == NULL || get_input_section_name == NULL ||
+      update_section_order == NULL || allow_section_ordering == NULL) {
+    fprintf(stderr, "Some interfaces are missing\n");
+    return LDPS_ERR;
+  }
+
+  return LDPS_OK;
+}
+
+// This function is called by the linker for every new object it encounters.
+enum ld_plugin_status claim_file_hook(const struct ld_plugin_input_file *file,
+                                      int *claimed)
+{
+  static bool is_ordering_specified = false;
+  struct ld_plugin_section section;
+  unsigned count = 0;
+  unsigned shndx;
+
+  *claimed = 0;
+  if (!is_ordering_specified) {
+    // Inform the linker to prepare for section reordering.
+    (*allow_section_ordering)();
+    is_ordering_specified = true;
+  }
+
+  (*get_input_section_count)(file->handle, &count);
+
+  for (shndx = 0; shndx < count; ++shndx) {
+    char *name = NULL;
+
+    section.handle = file->handle;
+    section.shndx = shndx;
+    (*get_input_section_name)(section, &name);
+    if (is_prefix_of(".data.v", name) ||
+        is_prefix_of(".bss.v", name) ||
+        is_prefix_of(".rodata.v", name)) {
+      SectionInfo si;
+      si.plugin_section.handle = file->handle;
+      si.plugin_section.shndx = shndx;
+      (*get_input_section_size)(section, &si.size);
+      (*get_input_section_alignment)(section, &si.align);
+      si.name = name;
+      si.flavor = flavor_from_name(name);
+      raw_sections.push_back(si);
+    }
+  }
+
+  return LDPS_OK;
+}
+
+// This function is called by the linker after all the symbols have been read.
+// At this stage, it is fine to tell the linker the desired function order.
+
+enum ld_plugin_status all_symbols_read_hook(void)
+{
+  // We expect to see a total of twelve sections -- if this is not the case
+  // then something went wrong somewhere along the way.
+  if (raw_sections.size() != 12) {
+    fprintf(stderr, "Expected 12 sections, found %u sections",
+            (unsigned) raw_sections.size());
+    return LDPS_ERR;
+  }
+
+  std::sort(raw_sections.begin(), raw_sections.end(),
+            SectionInfo::SectionInfoLt);
+
+  struct ld_plugin_section section_list[12];
+  for (unsigned ii = 0; ii < 12; ++ii) {
+    section_list[ii] = raw_sections[ii].plugin_section;
+  }
+
+  if (trace) {
+    fprintf(stderr, "Specified section order is:\n");
+    for (section_info_vector::iterator it = raw_sections.begin();
+         it != raw_sections.end();
+         ++it) {
+      const SectionInfo &si = (*it);
+      fprintf(stderr, "Idx=%u Name=%s Align=%u Size=%u\n",
+              si.plugin_section.shndx, si.name.c_str(), si.align,
+              (unsigned) si.size);
+    }
+  }
+
+  update_section_order(section_list, 12);
+
+  return LDPS_OK;
+}
+
+} // end extern "C"
diff --git a/include/plugin-api.h b/include/plugin-api.h
index d7f9ee3..3ee2e2b 100644
--- a/include/plugin-api.h
+++ b/include/plugin-api.h
@@ -345,6 +345,26 @@ enum ld_plugin_status
     const struct ld_plugin_section * section_list,
     unsigned int num_sections);

+/* The linker's interface for retrieving the section alignment requirement
+   of a specific section in an object.  This interface should only be
invoked in the
+   claim_file handler.  This function sets *ADDRALIGN to the ELF sh_addralign
+   value of the input section.  */
+
+typedef
+enum ld_plugin_status
+(*ld_plugin_get_input_section_alignment) (const struct
ld_plugin_section section,
+                                          unsigned int *addralign);
+
+/* The linker's interface for retrieving the section size of a specific section
+   in an object.  This interface should only be invoked in the
claim_file handler.
+   This function sets *SECSIZE to the ELF sh_size
+   value of the input section.  */
+
+typedef
+enum ld_plugin_status
+(*ld_plugin_get_input_section_size) (const struct ld_plugin_section section,
+                                     uint64_t *secsize);
+
 enum ld_plugin_level
 {
   LDPL_INFO,
@@ -384,7 +404,9 @@ enum ld_plugin_tag
   LDPT_ALLOW_SECTION_ORDERING = 24,
   LDPT_GET_SYMBOLS_V2 = 25,
   LDPT_ALLOW_UNIQUE_SEGMENT_FOR_SECTIONS = 26,
-  LDPT_UNIQUE_SEGMENT_FOR_SECTIONS = 27
+  LDPT_UNIQUE_SEGMENT_FOR_SECTIONS = 27,
+  LDPT_GET_INPUT_SECTION_ALIGNMENT = 28,
+  LDPT_GET_INPUT_SECTION_SIZE = 29
 };

 /* The plugin transfer vector.  */
@@ -416,6 +438,8 @@ struct ld_plugin_tv
     ld_plugin_allow_section_ordering tv_allow_section_ordering;
     ld_plugin_allow_unique_segment_for_sections
tv_allow_unique_segment_for_sections;
     ld_plugin_unique_segment_for_sections tv_unique_segment_for_sections;
+    ld_plugin_get_input_section_alignment tv_get_input_section_alignment;
+    ld_plugin_get_input_section_size tv_get_input_section_size;
   } tv_u;
 };