[lttng-ust.git] / liblttng-ust / lttng-ust-elf.c

/*
 * Copyright (C) 2015  Antoine Busque <abusque@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
 */

#define _GNU_SOURCE
#define _LGPL_SOURCE
#include <helper.h>
#include <string.h>
#include <lttng/align.h>
#include <lttng/ust-elf.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdbool.h>
#include "lttng-tracer-core.h"

#define BUF_LEN	4096

#ifndef NT_GNU_BUILD_ID
# define NT_GNU_BUILD_ID	3
#endif

/*
 * Retrieve the nth (where n is the `index` argument) phdr (program
 * header) from the given elf instance.
 *
 * A pointer to the phdr is returned on success, NULL on failure.
 */
static
struct lttng_ust_elf_phdr *lttng_ust_elf_get_phdr(struct lttng_ust_elf *elf,
						uint16_t index)
{
	struct lttng_ust_elf_phdr *phdr = NULL;
	off_t offset;

	if (!elf) {
		goto error;
	}

	if (index >= elf->ehdr->e_phnum) {
		goto error;
	}

	phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
	if (!phdr) {
		goto error;
	}

	offset = (off_t) elf->ehdr->e_phoff
			+ (off_t) index * elf->ehdr->e_phentsize;
	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
		goto error;
	}

	if (is_elf_32_bit(elf)) {
		Elf32_Phdr elf_phdr;

		if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
				< sizeof(elf_phdr)) {
			goto error;
		}
		if (!is_elf_native_endian(elf)) {
			bswap_phdr(elf_phdr);
		}
		copy_phdr(elf_phdr, *phdr);
	} else {
		Elf64_Phdr elf_phdr;

		if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
				< sizeof(elf_phdr)) {
			goto error;
		}
		if (!is_elf_native_endian(elf)) {
			bswap_phdr(elf_phdr);
		}
		copy_phdr(elf_phdr, *phdr);
	}

	return phdr;

error:
	free(phdr);
	return NULL;
}

/*
 * Retrieve the nth (where n is the `index` argument) shdr (section
 * header) from the given elf instance.
 *
 * A pointer to the shdr is returned on success, NULL on failure.
 */
static
struct lttng_ust_elf_shdr *lttng_ust_elf_get_shdr(struct lttng_ust_elf *elf,
						uint16_t index)
{
	struct lttng_ust_elf_shdr *shdr = NULL;
	off_t offset;

	if (!elf) {
		goto error;
	}

	if (index >= elf->ehdr->e_shnum) {
		goto error;
	}

	shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
	if (!shdr) {
		goto error;
	}

	offset = (off_t) elf->ehdr->e_shoff
			+ (off_t) index * elf->ehdr->e_shentsize;
	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
		goto error;
	}

	if (is_elf_32_bit(elf)) {
		Elf32_Shdr elf_shdr;

		if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
				< sizeof(elf_shdr)) {
			goto error;
		}
		if (!is_elf_native_endian(elf)) {
			bswap_shdr(elf_shdr);
		}
		copy_shdr(elf_shdr, *shdr);
	} else {
		Elf64_Shdr elf_shdr;

		if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
				< sizeof(elf_shdr)) {
			goto error;
		}
		if (!is_elf_native_endian(elf)) {
			bswap_shdr(elf_shdr);
		}
		copy_shdr(elf_shdr, *shdr);
	}

	return shdr;

error:
	free(shdr);
	return NULL;
}

/*
 * Lookup a section's name from a given offset (usually from an shdr's
 * sh_name value) in bytes relative to the beginning of the section
 * names string table.
 *
 * If no name is found, NULL is returned.
 */
static
char *lttng_ust_elf_get_section_name(struct lttng_ust_elf *elf, off_t offset)
{
	char *name = NULL;
	size_t len = 0, to_read;	/* len does not include \0 */

	if (!elf) {
		goto error;
	}

	if (offset >= elf->section_names_size) {
		goto error;
	}

	if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
		goto error;
	}

	to_read = elf->section_names_size - offset;

	/* Find first \0 after or at current location, remember len. */
	for (;;) {
		char buf[BUF_LEN];
		ssize_t read_len;
		size_t i;

		if (!to_read) {
			goto error;
		}
		read_len = lttng_ust_read(elf->fd, buf,
			min_t(size_t, BUF_LEN, to_read));
		if (read_len <= 0) {
			goto error;
		}
		for (i = 0; i < read_len; i++) {
			if (buf[i] == '\0') {
				len += i;
				goto end;
			}
		}
		len += read_len;
		to_read -= read_len;
	}
end:
	name = zmalloc(sizeof(char) * (len + 1));	/* + 1 for \0 */
	if (!name) {
		goto error;
	}
	if (lseek(elf->fd, elf->section_names_offset + offset,
		SEEK_SET) < 0) {
		goto error;
	}
	if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
		goto error;
	}

	return name;

error:
	free(name);
	return NULL;
}

/*
 * Create an instance of lttng_ust_elf for the ELF file located at
 * `path`.
 *
 * Return a pointer to the instance on success, NULL on failure.
 */
struct lttng_ust_elf *lttng_ust_elf_create(const char *path)
{
	uint8_t e_ident[EI_NIDENT];
	struct lttng_ust_elf_shdr *section_names_shdr;
	struct lttng_ust_elf *elf = NULL;

	elf = zmalloc(sizeof(struct lttng_ust_elf));
	if (!elf) {
		goto error;
	}

	elf->path = strdup(path);
	if (!elf->path) {
		goto error;
	}

	elf->fd = open(elf->path, O_RDONLY | O_CLOEXEC);
	if (elf->fd < 0) {
		goto error;
	}

	if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
		goto error;
	}
	elf->bitness = e_ident[EI_CLASS];
	elf->endianness = e_ident[EI_DATA];

	if (lseek(elf->fd, 0, SEEK_SET) < 0) {
		goto error;
	}

	elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
	if (!elf->ehdr) {
		goto error;
	}

	if (is_elf_32_bit(elf)) {
		Elf32_Ehdr elf_ehdr;

		if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
				< sizeof(elf_ehdr)) {
			goto error;
		}
		if (!is_elf_native_endian(elf)) {
			bswap_ehdr(elf_ehdr);
		}
		copy_ehdr(elf_ehdr, *(elf->ehdr));
	} else {
		Elf64_Ehdr elf_ehdr;

		if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
				< sizeof(elf_ehdr)) {
			goto error;
		}
		if (!is_elf_native_endian(elf)) {
			bswap_ehdr(elf_ehdr);
		}
		copy_ehdr(elf_ehdr, *(elf->ehdr));
	}

	section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
	if (!section_names_shdr) {
		goto error;
	}

	elf->section_names_offset = section_names_shdr->sh_offset;
	elf->section_names_size = section_names_shdr->sh_size;

	free(section_names_shdr);
	return elf;

error:
	if (elf) {
		free(elf->ehdr);
		if (elf->fd >= 0) {
			if (close(elf->fd)) {
				abort();
			}
		}
		free(elf->path);
		free(elf);
	}
	return NULL;
}

/*
 * Test whether the ELF file is position independent code (PIC)
 */
uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
{
	/*
	 * PIC has and e_type value of ET_DYN, see ELF specification
	 * version 1.1 p. 1-3.
	 */
	return elf->ehdr->e_type == ET_DYN;
}

/*
 * Destroy the given lttng_ust_elf instance.
 */
void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
{
	if (!elf) {
		return;
	}

	free(elf->ehdr);
	if (close(elf->fd)) {
		abort();
	}
	free(elf->path);
	free(elf);
}

/*
 * Compute the total in-memory size of the ELF file, in bytes.
 *
 * Returns 0 if successful, -1 if not. On success, the memory size is
 * returned through the out parameter `memsz`.
 */
int lttng_ust_elf_get_memsz(struct lttng_ust_elf *elf, uint64_t *memsz)
{
	uint16_t i;
	uint64_t low_addr = UINT64_MAX, high_addr = 0;

	if (!elf || !memsz) {
		goto error;
	}

	for (i = 0; i < elf->ehdr->e_phnum; ++i) {
		struct lttng_ust_elf_phdr *phdr;

		phdr = lttng_ust_elf_get_phdr(elf, i);
		if (!phdr) {
			goto error;
		}

		/*
		 * Only PT_LOAD segments contribute to memsz. Skip
		 * other segments.
		 */
		if (phdr->p_type != PT_LOAD) {
			goto next_loop;
		}

		low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
		high_addr = max_t(uint64_t, high_addr,
				phdr->p_vaddr + phdr->p_memsz);
	next_loop:
		free(phdr);
	}

	if (high_addr < low_addr) {
		/* No PT_LOAD segments or corrupted data. */
		goto error;
	}

	*memsz = high_addr - low_addr;
	return 0;
error:
	return -1;
}

/*
 * Internal method used to try and get the build_id from a PT_NOTE
 * segment ranging from `offset` to `segment_end`.
 *
 * If the function returns successfully, the out parameter `found`
 * indicates whether the build id information was present in the
 * segment or not. If `found` is not 0, the out parameters `build_id`
 * and `length` will both have been set with the retrieved
 * information.
 *
 * Returns 0 on success, -1 if an error occurred.
 */
static
int lttng_ust_elf_get_build_id_from_segment(
	struct lttng_ust_elf *elf, uint8_t **build_id, size_t *length,
	off_t offset, off_t segment_end)
{
	uint8_t *_build_id = NULL;	/* Silence old gcc warning. */
	size_t _length = 0;		/* Silence old gcc warning. */

	while (offset < segment_end) {
		struct lttng_ust_elf_nhdr nhdr;
		size_t read_len;

		/* Align start of note entry */
		offset += offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
		if (offset >= segment_end) {
			break;
		}
		/*
		 * We seek manually because if the note isn't the
		 * build id the data following the header will not
		 * have been read.
		 */
		if (lseek(elf->fd, offset, SEEK_SET) < 0) {
			goto error;
		}
		if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
				< sizeof(nhdr)) {
			goto error;
		}

		if (!is_elf_native_endian(elf)) {
			nhdr.n_namesz = bswap_32(nhdr.n_namesz);
			nhdr.n_descsz = bswap_32(nhdr.n_descsz);
			nhdr.n_type = bswap_32(nhdr.n_type);
		}

		offset += sizeof(nhdr) + nhdr.n_namesz;
		/* Align start of desc entry */
		offset += offset_align(offset, ELF_NOTE_DESC_ALIGN);

		if (nhdr.n_type != NT_GNU_BUILD_ID) {
			/*
			 * Ignore non build id notes but still
			 * increase the offset.
			 */
			offset += nhdr.n_descsz;
			continue;
		}

		_length = nhdr.n_descsz;
		_build_id = zmalloc(sizeof(uint8_t) * _length);
		if (!_build_id) {
			goto error;
		}

		if (lseek(elf->fd, offset, SEEK_SET) < 0) {
			goto error;
		}
		read_len = sizeof(*_build_id) * _length;
		if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
			goto error;
		}

		break;
	}

	if (_build_id) {
		*build_id = _build_id;
		*length = _length;
	}

	return 0;
error:
	free(_build_id);
	return -1;
}

/*
 * Retrieve a build ID (an array of bytes) from the corresponding
 * section in the ELF file. The length of the build ID can be either
 * 16 or 20 bytes depending on the method used to generate it, hence
 * the length out parameter.
 *
 * If the function returns successfully, the out parameter `found`
 * indicates whether the build id information was present in the ELF
 * file or not. If `found` is not 0, the out parameters `build_id` and
 * `length` will both have been set with the retrieved information.
 *
 * Returns 0 on success, -1 if an error occurred.
 */
int lttng_ust_elf_get_build_id(struct lttng_ust_elf *elf, uint8_t **build_id,
			size_t *length, int *found)
{
	uint16_t i;
	uint8_t *_build_id = NULL;	/* Silence old gcc warning. */
	size_t _length = 0;		/* Silence old gcc warning. */

	if (!elf || !build_id || !length || !found) {
		goto error;
	}

	for (i = 0; i < elf->ehdr->e_phnum; ++i) {
		off_t offset, segment_end;
		struct lttng_ust_elf_phdr *phdr;
		int ret = 0;

		phdr = lttng_ust_elf_get_phdr(elf, i);
		if (!phdr) {
			goto error;
		}

		/* Build ID will be contained in a PT_NOTE segment. */
		if (phdr->p_type != PT_NOTE) {
			goto next_loop;
		}

		offset = phdr->p_offset;
		segment_end = offset + phdr->p_filesz;
		ret = lttng_ust_elf_get_build_id_from_segment(
			elf, &_build_id, &_length, offset, segment_end);
	next_loop:
		free(phdr);
		if (ret) {
			goto error;
		}
		if (_build_id) {
			break;
		}
	}

	if (_build_id) {
		*build_id = _build_id;
		*length = _length;
		*found = 1;
	} else {
		*found = 0;
	}

	return 0;
error:
	free(_build_id);
	return -1;
}

/*
 * Try to retrieve filename and CRC from given ELF section `shdr`.
 *
 * If the function returns successfully, the out parameter `found`
 * indicates whether the debug link information was present in the ELF
 * section or not. If `found` is not 0, the out parameters `filename` and
 * `crc` will both have been set with the retrieved information.
 *
 * Returns 0 on success, -1 if an error occurred.
 */
int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
					char **filename, uint32_t *crc,
					struct lttng_ust_elf_shdr *shdr)
{
	char *_filename = NULL;		/* Silence old gcc warning. */
	size_t filename_len;
	char *section_name = NULL;
	uint32_t _crc = 0;		/* Silence old gcc warning. */

	if (!elf || !filename || !crc || !shdr) {
		goto error;
	}

	/*
	 * The .gnu_debuglink section is of type SHT_PROGBITS,
	 * skip the other sections.
	 */
	if (shdr->sh_type != SHT_PROGBITS) {
		goto end;
	}

	section_name = lttng_ust_elf_get_section_name(elf,
						shdr->sh_name);
	if (!section_name) {
		goto end;
	}
	if (strcmp(section_name, ".gnu_debuglink")) {
		goto end;
	}

	/*
	 * The length of the filename is the sh_size excluding the CRC
	 * which comes after it in the section.
	 */
	_filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
	if (!_filename) {
		goto error;
	}
	if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
		goto error;
	}
	filename_len = sizeof(*_filename) * (shdr->sh_size - ELF_CRC_SIZE);
	if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
		goto error;
	}
	if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
		goto error;
	}
	if (!is_elf_native_endian(elf)) {
		_crc = bswap_32(_crc);
	}

end:
	free(section_name);
	if (_filename) {
		*filename = _filename;
		*crc = _crc;
	}

	return 0;

error:
	free(_filename);
	free(section_name);
	return -1;
}

/*
 * Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
 *
 * If the function returns successfully, the out parameter `found`
 * indicates whether the debug link information was present in the ELF
 * file or not. If `found` is not 0, the out parameters `filename` and
 * `crc` will both have been set with the retrieved information.
 *
 * Returns 0 on success, -1 if an error occurred.
 */
int lttng_ust_elf_get_debug_link(struct lttng_ust_elf *elf, char **filename,
				uint32_t *crc, int *found)
{
	int ret;
	uint16_t i;
	char *_filename = NULL;		/* Silence old gcc warning. */
	uint32_t _crc = 0;		/* Silence old gcc warning. */

	if (!elf || !filename || !crc || !found) {
		goto error;
	}

	for (i = 0; i < elf->ehdr->e_shnum; ++i) {
		struct lttng_ust_elf_shdr *shdr = NULL;

		shdr = lttng_ust_elf_get_shdr(elf, i);
		if (!shdr) {
			goto error;
		}

		ret = lttng_ust_elf_get_debug_link_from_section(
			elf, &_filename, &_crc, shdr);
		free(shdr);

		if (ret) {
			goto error;
		}
		if (_filename) {
			break;
		}
	}

	if (_filename) {
		*filename = _filename;
		*crc = _crc;
		*found = 1;
	} else {
		*found = 0;
	}

	return 0;

error:
	free(_filename);
	return -1;
}
Commit	Line	Data
8e2aed3f AB	1	/*
	2	* Copyright (C) 2015 Antoine Busque <abusque@efficios.com>
	3	*
	4	* This library is free software; you can redistribute it and/or
	5	* modify it under the terms of the GNU Lesser General Public
	6	* License as published by the Free Software Foundation; either
	7	* version 2.1 of the License, or (at your option) any later version.
	8	*
	9	* This library is distributed in the hope that it will be useful,
	10	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	11	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	12	* Lesser General Public License for more details.
	13	*
	14	* You should have received a copy of the GNU Lesser General Public
	15	* License along with this library; if not, write to the Free Software
	16	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	17	*/
	18
aaf93c60	19	#define _GNU_SOURCE
3fbec7dc	20	#define _LGPL_SOURCE
8e2aed3f AB	21	#include <helper.h>
	22	#include <string.h>
	23	#include <lttng/align.h>
	24	#include <lttng/ust-elf.h>
405be658 MD	25	#include <sys/types.h>
	26	#include <sys/stat.h>
	27	#include <fcntl.h>
	28	#include <unistd.h>
97c7c238	29	#include <stdbool.h>
405be658 MD	30	#include "lttng-tracer-core.h"
	31
	32	#define BUF_LEN 4096
8e2aed3f	33
e9dbbd6e PP	34	#ifndef NT_GNU_BUILD_ID
	35	# define NT_GNU_BUILD_ID 3
	36	#endif
	37
8e2aed3f AB	38	/*
	39	* Retrieve the nth (where n is the `index` argument) phdr (program
	40	* header) from the given elf instance.
	41	*
	42	* A pointer to the phdr is returned on success, NULL on failure.
	43	*/
	44	static
	45	struct lttng_ust_elf_phdr lttng_ust_elf_get_phdr(struct lttng_ust_elf elf,
	46	uint16_t index)
	47	{
	48	struct lttng_ust_elf_phdr *phdr = NULL;
f5a6717a	49	off_t offset;
8e2aed3f AB	50
	51	if (!elf) {
	52	goto error;
	53	}
	54
	55	if (index >= elf->ehdr->e_phnum) {
	56	goto error;
	57	}
	58
	59	phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
	60	if (!phdr) {
	61	goto error;
	62	}
	63
f5a6717a MD	64	offset = (off_t) elf->ehdr->e_phoff
f5a6717a MD	65	+ (off_t) index * elf->ehdr->e_phentsize;
405be658	66	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	67	goto error;
	68	}
	69
	70	if (is_elf_32_bit(elf)) {
	71	Elf32_Phdr elf_phdr;
	72
405be658 MD	73	if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
405be658 MD	74	< sizeof(elf_phdr)) {
8e2aed3f AB	75	goto error;
	76	}
	77	if (!is_elf_native_endian(elf)) {
	78	bswap_phdr(elf_phdr);
	79	}
	80	copy_phdr(elf_phdr, *phdr);
	81	} else {
	82	Elf64_Phdr elf_phdr;
	83
405be658 MD	84	if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
405be658 MD	85	< sizeof(elf_phdr)) {
8e2aed3f AB	86	goto error;
	87	}
	88	if (!is_elf_native_endian(elf)) {
	89	bswap_phdr(elf_phdr);
	90	}
	91	copy_phdr(elf_phdr, *phdr);
	92	}
	93
	94	return phdr;
	95
	96	error:
	97	free(phdr);
	98	return NULL;
	99	}
	100
	101	/*
	102	* Retrieve the nth (where n is the `index` argument) shdr (section
	103	* header) from the given elf instance.
	104	*
	105	* A pointer to the shdr is returned on success, NULL on failure.
	106	*/
	107	static
	108	struct lttng_ust_elf_shdr lttng_ust_elf_get_shdr(struct lttng_ust_elf elf,
	109	uint16_t index)
	110	{
	111	struct lttng_ust_elf_shdr *shdr = NULL;
4c5dac0d	112	off_t offset;
8e2aed3f AB	113
	114	if (!elf) {
	115	goto error;
	116	}
	117
	118	if (index >= elf->ehdr->e_shnum) {
	119	goto error;
	120	}
	121
	122	shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
	123	if (!shdr) {
	124	goto error;
	125	}
	126
4c5dac0d	127	offset = (off_t) elf->ehdr->e_shoff
5a26ac54	128	+ (off_t) index * elf->ehdr->e_shentsize;
405be658	129	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	130	goto error;
	131	}
	132
	133	if (is_elf_32_bit(elf)) {
	134	Elf32_Shdr elf_shdr;
	135
405be658 MD	136	if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
405be658 MD	137	< sizeof(elf_shdr)) {
8e2aed3f AB	138	goto error;
	139	}
	140	if (!is_elf_native_endian(elf)) {
	141	bswap_shdr(elf_shdr);
	142	}
	143	copy_shdr(elf_shdr, *shdr);
	144	} else {
	145	Elf64_Shdr elf_shdr;
	146
405be658 MD	147	if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
405be658 MD	148	< sizeof(elf_shdr)) {
8e2aed3f AB	149	goto error;
	150	}
	151	if (!is_elf_native_endian(elf)) {
	152	bswap_shdr(elf_shdr);
	153	}
	154	copy_shdr(elf_shdr, *shdr);
	155	}
	156
	157	return shdr;
	158
	159	error:
	160	free(shdr);
	161	return NULL;
	162	}
	163
	164	/*
	165	* Lookup a section's name from a given offset (usually from an shdr's
	166	* sh_name value) in bytes relative to the beginning of the section
	167	* names string table.
	168	*
	169	* If no name is found, NULL is returned.
	170	*/
	171	static
f5a6717a	172	char lttng_ust_elf_get_section_name(struct lttng_ust_elf elf, off_t offset)
8e2aed3f AB	173	{
8e2aed3f AB	174	char *name = NULL;
405be658	175	size_t len = 0, to_read; /* len does not include \0 */
8e2aed3f AB	176
	177	if (!elf) {
	178	goto error;
	179	}
	180
	181	if (offset >= elf->section_names_size) {
	182	goto error;
	183	}
	184
405be658	185	if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
8e2aed3f AB	186	goto error;
8e2aed3f AB	187	}
405be658 MD	188
	189	to_read = elf->section_names_size - offset;
	190
	191	/* Find first \0 after or at current location, remember len. */
	192	for (;;) {
	193	char buf[BUF_LEN];
	194	ssize_t read_len;
	195	size_t i;
	196
	197	if (!to_read) {
8e2aed3f	198	goto error;
8e2aed3f	199	}
405be658 MD	200	read_len = lttng_ust_read(elf->fd, buf,
	201	min_t(size_t, BUF_LEN, to_read));
	202	if (read_len <= 0) {
	203	goto error;
	204	}
	205	for (i = 0; i < read_len; i++) {
	206	if (buf[i] == '\0') {
	207	len += i;
	208	goto end;
	209	}
	210	}
	211	len += read_len;
	212	to_read -= read_len;
8e2aed3f	213	}
8e2aed3f	214	end:
405be658	215	name = zmalloc(sizeof(char) * (len + 1)); /* + 1 for \0 */
8e2aed3f AB	216	if (!name) {
	217	goto error;
	218	}
405be658 MD	219	if (lseek(elf->fd, elf->section_names_offset + offset,
405be658 MD	220	SEEK_SET) < 0) {
8e2aed3f AB	221	goto error;
8e2aed3f AB	222	}
405be658	223	if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
8e2aed3f AB	224	goto error;
	225	}
	226
	227	return name;
	228
	229	error:
	230	free(name);
	231	return NULL;
	232	}
	233
	234	/*
	235	* Create an instance of lttng_ust_elf for the ELF file located at
	236	* `path`.
	237	*
	238	* Return a pointer to the instance on success, NULL on failure.
	239	*/
	240	struct lttng_ust_elf lttng_ust_elf_create(const char path)
	241	{
	242	uint8_t e_ident[EI_NIDENT];
	243	struct lttng_ust_elf_shdr *section_names_shdr;
405be658	244	struct lttng_ust_elf *elf = NULL;
8e2aed3f AB	245
	246	elf = zmalloc(sizeof(struct lttng_ust_elf));
	247	if (!elf) {
	248	goto error;
	249	}
	250
	251	elf->path = strdup(path);
	252	if (!elf->path) {
	253	goto error;
	254	}
	255
405be658 MD	256	elf->fd = open(elf->path, O_RDONLY \| O_CLOEXEC);
405be658 MD	257	if (elf->fd < 0) {
8e2aed3f AB	258	goto error;
	259	}
	260
405be658	261	if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
8e2aed3f AB	262	goto error;
	263	}
	264	elf->bitness = e_ident[EI_CLASS];
	265	elf->endianness = e_ident[EI_DATA];
405be658 MD	266
	267	if (lseek(elf->fd, 0, SEEK_SET) < 0) {
	268	goto error;
	269	}
8e2aed3f AB	270
	271	elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
	272	if (!elf->ehdr) {
	273	goto error;
	274	}
	275
	276	if (is_elf_32_bit(elf)) {
	277	Elf32_Ehdr elf_ehdr;
	278
405be658 MD	279	if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
405be658 MD	280	< sizeof(elf_ehdr)) {
8e2aed3f AB	281	goto error;
	282	}
	283	if (!is_elf_native_endian(elf)) {
	284	bswap_ehdr(elf_ehdr);
	285	}
	286	copy_ehdr(elf_ehdr, *(elf->ehdr));
	287	} else {
	288	Elf64_Ehdr elf_ehdr;
	289
405be658 MD	290	if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
405be658 MD	291	< sizeof(elf_ehdr)) {
8e2aed3f AB	292	goto error;
	293	}
	294	if (!is_elf_native_endian(elf)) {
	295	bswap_ehdr(elf_ehdr);
	296	}
	297	copy_ehdr(elf_ehdr, *(elf->ehdr));
	298	}
	299
	300	section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
	301	if (!section_names_shdr) {
	302	goto error;
	303	}
	304
	305	elf->section_names_offset = section_names_shdr->sh_offset;
	306	elf->section_names_size = section_names_shdr->sh_size;
	307
	308	free(section_names_shdr);
8e2aed3f AB	309	return elf;
	310
	311	error:
	312	if (elf) {
	313	free(elf->ehdr);
405be658 MD	314	if (elf->fd >= 0) {
	315	if (close(elf->fd)) {
	316	abort();
	317	}
	318	}
8e2aed3f	319	free(elf->path);
405be658	320	free(elf);
8e2aed3f	321	}
8e2aed3f AB	322	return NULL;
	323	}
	324
f5eb039d AB	325	/*
	326	* Test whether the ELF file is position independent code (PIC)
	327	*/
	328	uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
	329	{
	330	/*
	331	* PIC has and e_type value of ET_DYN, see ELF specification
	332	* version 1.1 p. 1-3.
	333	*/
	334	return elf->ehdr->e_type == ET_DYN;
	335	}
	336
8e2aed3f AB	337	/*
	338	* Destroy the given lttng_ust_elf instance.
	339	*/
	340	void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
	341	{
	342	if (!elf) {
	343	return;
	344	}
	345
	346	free(elf->ehdr);
405be658 MD	347	if (close(elf->fd)) {
	348	abort();
	349	}
8e2aed3f AB	350	free(elf->path);
	351	free(elf);
	352	}
	353
	354	/*
	355	* Compute the total in-memory size of the ELF file, in bytes.
	356	*
	357	* Returns 0 if successful, -1 if not. On success, the memory size is
	358	* returned through the out parameter `memsz`.
	359	*/
	360	int lttng_ust_elf_get_memsz(struct lttng_ust_elf elf, uint64_t memsz)
	361	{
	362	uint16_t i;
e1f0c569	363	uint64_t low_addr = UINT64_MAX, high_addr = 0;
8e2aed3f AB	364
	365	if (!elf \|\| !memsz) {
	366	goto error;
	367	}
	368
	369	for (i = 0; i < elf->ehdr->e_phnum; ++i) {
	370	struct lttng_ust_elf_phdr *phdr;
8e2aed3f AB	371
	372	phdr = lttng_ust_elf_get_phdr(elf, i);
	373	if (!phdr) {
	374	goto error;
	375	}
	376
	377	/*
	378	* Only PT_LOAD segments contribute to memsz. Skip
	379	* other segments.
	380	*/
	381	if (phdr->p_type != PT_LOAD) {
	382	goto next_loop;
	383	}
	384
8886accb MD	385	low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
	386	high_addr = max_t(uint64_t, high_addr,
	387	phdr->p_vaddr + phdr->p_memsz);
8e2aed3f AB	388	next_loop:
	389	free(phdr);
	390	}
	391
e1f0c569 AB	392	if (high_addr < low_addr) {
	393	/* No PT_LOAD segments or corrupted data. */
	394	goto error;
	395	}
	396
	397	*memsz = high_addr - low_addr;
8e2aed3f AB	398	return 0;
	399	error:
	400	return -1;
	401	}
	402
	403	/*
	404	* Internal method used to try and get the build_id from a PT_NOTE
	405	* segment ranging from `offset` to `segment_end`.
	406	*
	407	* If the function returns successfully, the out parameter `found`
	408	* indicates whether the build id information was present in the
	409	* segment or not. If `found` is not 0, the out parameters `build_id`
	410	* and `length` will both have been set with the retrieved
	411	* information.
	412	*
	413	* Returns 0 on success, -1 if an error occurred.
	414	*/
	415	static
	416	int lttng_ust_elf_get_build_id_from_segment(
	417	struct lttng_ust_elf elf, uint8_t build_id, size_t length,
82ee1ee4	418	off_t offset, off_t segment_end)
8e2aed3f	419	{
814d07b1 MD	420	uint8_t _build_id = NULL; / Silence old gcc warning. */
814d07b1 MD	421	size_t _length = 0; /* Silence old gcc warning. */
8e2aed3f AB	422
	423	while (offset < segment_end) {
	424	struct lttng_ust_elf_nhdr nhdr;
405be658	425	size_t read_len;
8e2aed3f AB	426
	427	/* Align start of note entry */
	428	offset += offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
	429	if (offset >= segment_end) {
	430	break;
	431	}
	432	/*
	433	* We seek manually because if the note isn't the
	434	* build id the data following the header will not
	435	* have been read.
	436	*/
405be658	437	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	438	goto error;
8e2aed3f AB	439	}
405be658 MD	440	if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
405be658 MD	441	< sizeof(nhdr)) {
8e2aed3f AB	442	goto error;
	443	}
	444
	445	if (!is_elf_native_endian(elf)) {
	446	nhdr.n_namesz = bswap_32(nhdr.n_namesz);
	447	nhdr.n_descsz = bswap_32(nhdr.n_descsz);
	448	nhdr.n_type = bswap_32(nhdr.n_type);
	449	}
	450
	451	offset += sizeof(nhdr) + nhdr.n_namesz;
	452	/* Align start of desc entry */
	453	offset += offset_align(offset, ELF_NOTE_DESC_ALIGN);
	454
	455	if (nhdr.n_type != NT_GNU_BUILD_ID) {
	456	/*
	457	* Ignore non build id notes but still
	458	* increase the offset.
	459	*/
	460	offset += nhdr.n_descsz;
	461	continue;
	462	}
	463
	464	_length = nhdr.n_descsz;
	465	_build_id = zmalloc(sizeof(uint8_t) * _length);
5ada26b4	466	if (!_build_id) {
8e2aed3f AB	467	goto error;
	468	}
	469
405be658	470	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	471	goto error;
8e2aed3f AB	472	}
405be658 MD	473	read_len = sizeof(_build_id) _length;
405be658 MD	474	if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
8e2aed3f AB	475	goto error;
	476	}
	477
8e2aed3f AB	478	break;
	479	}
	480
82ee1ee4	481	if (_build_id) {
8e2aed3f AB	482	*build_id = _build_id;
	483	*length = _length;
	484	}
	485
8e2aed3f AB	486	return 0;
8e2aed3f AB	487	error:
83215d66	488	free(_build_id);
8e2aed3f AB	489	return -1;
	490	}
	491
	492	/*
	493	* Retrieve a build ID (an array of bytes) from the corresponding
	494	* section in the ELF file. The length of the build ID can be either
	495	* 16 or 20 bytes depending on the method used to generate it, hence
	496	* the length out parameter.
	497	*
	498	* If the function returns successfully, the out parameter `found`
	499	* indicates whether the build id information was present in the ELF
	500	* file or not. If `found` is not 0, the out parameters `build_id` and
	501	* `length` will both have been set with the retrieved information.
	502	*
	503	* Returns 0 on success, -1 if an error occurred.
	504	*/
	505	int lttng_ust_elf_get_build_id(struct lttng_ust_elf elf, uint8_t *build_id,
	506	size_t length, int found)
	507	{
	508	uint16_t i;
8c83dbda MD	509	uint8_t _build_id = NULL; / Silence old gcc warning. */
8c83dbda MD	510	size_t _length = 0; /* Silence old gcc warning. */
8e2aed3f AB	511
	512	if (!elf \|\| !build_id \|\| !length \|\| !found) {
	513	goto error;
	514	}
	515
	516	for (i = 0; i < elf->ehdr->e_phnum; ++i) {
f5a6717a	517	off_t offset, segment_end;
8e2aed3f	518	struct lttng_ust_elf_phdr *phdr;
5b3bbf98	519	int ret = 0;
8e2aed3f AB	520
	521	phdr = lttng_ust_elf_get_phdr(elf, i);
	522	if (!phdr) {
	523	goto error;
	524	}
	525
	526	/* Build ID will be contained in a PT_NOTE segment. */
	527	if (phdr->p_type != PT_NOTE) {
	528	goto next_loop;
	529	}
	530
	531	offset = phdr->p_offset;
	532	segment_end = offset + phdr->p_filesz;
	533	ret = lttng_ust_elf_get_build_id_from_segment(
82ee1ee4	534	elf, &_build_id, &_length, offset, segment_end);
8e2aed3f AB	535	next_loop:
	536	free(phdr);
	537	if (ret) {
	538	goto error;
	539	}
82ee1ee4	540	if (_build_id) {
8e2aed3f AB	541	break;
	542	}
	543	}
	544
82ee1ee4	545	if (_build_id) {
8e2aed3f AB	546	*build_id = _build_id;
8e2aed3f AB	547	*length = _length;
82ee1ee4 AB	548	*found = 1;
	549	} else {
	550	*found = 0;
8e2aed3f AB	551	}
8e2aed3f AB	552
8e2aed3f AB	553	return 0;
8e2aed3f AB	554	error:
99b7132d	555	free(_build_id);
8e2aed3f AB	556	return -1;
	557	}
	558
	559	/*
	560	* Try to retrieve filename and CRC from given ELF section `shdr`.
	561	*
	562	* If the function returns successfully, the out parameter `found`
	563	* indicates whether the debug link information was present in the ELF
	564	* section or not. If `found` is not 0, the out parameters `filename` and
	565	* `crc` will both have been set with the retrieved information.
	566	*
	567	* Returns 0 on success, -1 if an error occurred.
	568	*/
8e2aed3f AB	569	int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
8e2aed3f AB	570	char *filename, uint32_t crc,
8e2aed3f AB	571	struct lttng_ust_elf_shdr *shdr)
8e2aed3f AB	572	{
8c83dbda	573	char _filename = NULL; / Silence old gcc warning. */
405be658	574	size_t filename_len;
8e2aed3f	575	char *section_name = NULL;
8c83dbda	576	uint32_t _crc = 0; /* Silence old gcc warning. */
8e2aed3f	577
82ee1ee4	578	if (!elf \|\| !filename \|\| !crc \|\| !shdr) {
8e2aed3f AB	579	goto error;
	580	}
	581
	582	/*
	583	* The .gnu_debuglink section is of type SHT_PROGBITS,
	584	* skip the other sections.
	585	*/
	586	if (shdr->sh_type != SHT_PROGBITS) {
	587	goto end;
	588	}
	589
	590	section_name = lttng_ust_elf_get_section_name(elf,
	591	shdr->sh_name);
	592	if (!section_name) {
	593	goto end;
	594	}
	595	if (strcmp(section_name, ".gnu_debuglink")) {
	596	goto end;
	597	}
	598
	599	/*
	600	* The length of the filename is the sh_size excluding the CRC
	601	* which comes after it in the section.
	602	*/
	603	_filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
	604	if (!_filename) {
	605	goto error;
	606	}
405be658	607	if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
8e2aed3f AB	608	goto error;
8e2aed3f AB	609	}
405be658 MD	610	filename_len = sizeof(_filename) (shdr->sh_size - ELF_CRC_SIZE);
405be658 MD	611	if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
8e2aed3f AB	612	goto error;
8e2aed3f AB	613	}
405be658	614	if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
8e2aed3f AB	615	goto error;
	616	}
	617	if (!is_elf_native_endian(elf)) {
	618	_crc = bswap_32(_crc);
	619	}
	620
8e2aed3f AB	621	end:
8e2aed3f AB	622	free(section_name);
82ee1ee4	623	if (_filename) {
8e2aed3f AB	624	*filename = _filename;
	625	*crc = _crc;
	626	}
8e2aed3f AB	627
	628	return 0;
	629
	630	error:
83215d66 MD	631	free(_filename);
83215d66 MD	632	free(section_name);
8e2aed3f AB	633	return -1;
	634	}
	635
	636	/*
	637	* Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
	638	*
	639	* If the function returns successfully, the out parameter `found`
	640	* indicates whether the debug link information was present in the ELF
	641	* file or not. If `found` is not 0, the out parameters `filename` and
	642	* `crc` will both have been set with the retrieved information.
	643	*
	644	* Returns 0 on success, -1 if an error occurred.
	645	*/
	646	int lttng_ust_elf_get_debug_link(struct lttng_ust_elf elf, char *filename,
	647	uint32_t crc, int found)
	648	{
	649	int ret;
	650	uint16_t i;
8c83dbda MD	651	char _filename = NULL; / Silence old gcc warning. */
8c83dbda MD	652	uint32_t _crc = 0; /* Silence old gcc warning. */
8e2aed3f AB	653
	654	if (!elf \|\| !filename \|\| !crc \|\| !found) {
	655	goto error;
	656	}
	657
	658	for (i = 0; i < elf->ehdr->e_shnum; ++i) {
	659	struct lttng_ust_elf_shdr *shdr = NULL;
	660
	661	shdr = lttng_ust_elf_get_shdr(elf, i);
	662	if (!shdr) {
	663	goto error;
	664	}
	665
	666	ret = lttng_ust_elf_get_debug_link_from_section(
82ee1ee4	667	elf, &_filename, &_crc, shdr);
8e2aed3f AB	668	free(shdr);
	669
	670	if (ret) {
	671	goto error;
	672	}
82ee1ee4	673	if (_filename) {
8e2aed3f AB	674	break;
	675	}
	676	}
	677
82ee1ee4	678	if (_filename) {
8e2aed3f AB	679	*filename = _filename;
8e2aed3f AB	680	*crc = _crc;
82ee1ee4 AB	681	*found = 1;
	682	} else {
	683	*found = 0;
8e2aed3f AB	684	}
8e2aed3f AB	685
8e2aed3f	686	return 0;
82ee1ee4	687
8e2aed3f	688	error:
99b7132d	689	free(_filename);
8e2aed3f AB	690	return -1;
8e2aed3f AB	691	}