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/* plugin_new_section_layout.c -- Simple plugin to reorder function sections in
plugin-generated objects
Copyright (C) 2017-2024 Free Software Foundation, Inc.
Written by Stephen Crane <sjc@immunant.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. */
/* This plugin tests the new_input API of the linker plugin interface that
* allows plugins to modify section layout and assign sections to segments for
* sections in plugin-generated object files. It assumes that another plugin is
* also in use which will add new files. In practice a plugin is likely to
* generate new input files itself in all_symbols_read and want to
* reorder/assign sections for these files in the new_input_hook callback. */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "plugin-api.h"
#include "elf/common.h"
static ld_plugin_get_input_section_count get_input_section_count = NULL;
static ld_plugin_get_input_section_type get_input_section_type = 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;
static ld_plugin_allow_unique_segment_for_sections
allow_unique_segment_for_sections = NULL;
static ld_plugin_unique_segment_for_sections unique_segment_for_sections = NULL;
enum ld_plugin_status onload(struct ld_plugin_tv *tv);
enum ld_plugin_status new_input_hook(const struct ld_plugin_input_file *file);
/* 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_GET_INPUT_SECTION_COUNT:
get_input_section_count = *entry->tv_u.tv_get_input_section_count;
break;
case LDPT_GET_INPUT_SECTION_TYPE:
get_input_section_type = *entry->tv_u.tv_get_input_section_type;
break;
case LDPT_GET_INPUT_SECTION_NAME:
get_input_section_name = *entry->tv_u.tv_get_input_section_name;
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;
case LDPT_ALLOW_UNIQUE_SEGMENT_FOR_SECTIONS:
allow_unique_segment_for_sections
= *entry->tv_u.tv_allow_unique_segment_for_sections;
break;
case LDPT_UNIQUE_SEGMENT_FOR_SECTIONS:
unique_segment_for_sections
= *entry->tv_u.tv_unique_segment_for_sections;
break;
case LDPT_REGISTER_NEW_INPUT_HOOK:
assert((*entry->tv_u.tv_register_new_input) (new_input_hook)
== LDPS_OK);
break;
default:
break;
}
}
if (get_input_section_count == NULL
|| get_input_section_type == NULL
|| get_input_section_name == NULL
|| update_section_order == NULL
|| allow_section_ordering == NULL
|| allow_unique_segment_for_sections == NULL
|| unique_segment_for_sections == NULL)
{
fprintf(stderr, "Some interfaces are missing\n");
return LDPS_ERR;
}
/* Inform the linker to prepare for section reordering. */
(*allow_section_ordering)();
/* Inform the linker to prepare to map some sections to unique
segments. */
(*allow_unique_segment_for_sections)();
return LDPS_OK;
}
inline static int is_prefix_of(const char *prefix, const char *str)
{
return strncmp(prefix, str, strlen (prefix)) == 0;
}
/* This function is called by the linker when new files are added by a plugin.
We can now tell the linker the desired function order since we have a file
handle for the newly added file. */
enum ld_plugin_status
new_input_hook(const struct ld_plugin_input_file *file)
{
struct ld_plugin_section section_list[3];
int num_entries = 0;
unsigned int count;
if (get_input_section_count(file->handle, &count) != LDPS_OK)
return LDPS_ERR;
unsigned int i;
for (i = 0; i < count; ++i)
{
struct ld_plugin_section section;
unsigned int type = 0;
char *name = NULL;
int position = 3;
section.handle = file->handle;
section.shndx = i;
if (get_input_section_type(section, &type) != LDPS_OK)
return LDPS_ERR;
if (type != SHT_PROGBITS)
continue;
if (get_input_section_name(section, &name))
return LDPS_ERR;
/* As in plugin_section_order.c, order is foo() followed by bar()
followed by baz() */
if (is_prefix_of(".text.", name))
{
if (strstr(name, "_Z3foov") != NULL)
position = 0;
else if (strstr(name, "_Z3barv") != NULL)
position = 1;
else if (strstr(name, "_Z3bazv") != NULL)
position = 2;
else
position = 3;
}
if (position < 3)
{
section_list[position] = section;
num_entries++;
}
}
if (num_entries != 3)
return LDPS_ERR;
update_section_order(section_list, num_entries);
unique_segment_for_sections (".text.plugin_created_unique", 0, 0x1000,
section_list, num_entries);
return LDPS_OK;
}
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