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

/*
 * SPDX-License-Identifier: LGPL-2.1-or-later
 *
 * Copyright (C) 2015 Antoine Busque <abusque@efficios.com>
 */

#define _LGPL_SOURCE
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <lttng/ust-utils.h>

#include <ust-elf.h>
#include <ust-fd.h>

#include "lttng-tracer-core.h"
#include "lttng-ust-elf.h"
#include "ust-helper.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;
	int ret, fd;

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

	/* Initialize fd field to -1. 0 is a valid fd number */
	elf->fd = -1;

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

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

	ret = lttng_ust_add_fd_to_tracker(fd);
	if (ret < 0) {
		ret = close(fd);
		if (ret) {
			PERROR("close on elf->fd");
		}
		ret = -1;
		lttng_ust_unlock_fd_tracker();
		goto error;
	}
	elf->fd = ret;
	lttng_ust_unlock_fd_tracker();

	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:
	lttng_ust_elf_destroy(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)
{
	int ret;

	if (!elf) {
		return;
	}

	if (elf->fd >= 0) {
		lttng_ust_lock_fd_tracker();
		ret = close(elf->fd);
		if (!ret) {
			lttng_ust_delete_fd_from_tracker(elf->fd);
		} else {
			PERROR("close");
			abort();
		}
		lttng_ust_unlock_fd_tracker();
	}

	free(elf->ehdr);
	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 += lttng_ust_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 += lttng_ust_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.
 */
static
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	1	/*
c0c0989a	2	* SPDX-License-Identifier: LGPL-2.1-or-later
8e2aed3f	3	*
c0c0989a	4	* Copyright (C) 2015 Antoine Busque <abusque@efficios.com>
8e2aed3f AB	5	*/
8e2aed3f AB	6
3fbec7dc	7	#define _LGPL_SOURCE
fb31eb73	8	#include <fcntl.h>
fb31eb73 FD	9	#include <stdbool.h>
	10	#include <stdint.h>
	11	#include <string.h>
405be658	12	#include <sys/stat.h>
fb31eb73	13	#include <sys/types.h>
405be658	14	#include <unistd.h>
fb31eb73	15
eae3c729	16	#include <lttng/ust-utils.h>
3d3a2bb8 MJ	17
3d3a2bb8 MJ	18	#include <ust-elf.h>
ba8dcc8c	19	#include <ust-fd.h>
fb31eb73	20
405be658	21	#include "lttng-tracer-core.h"
2a8db464	22	#include "lttng-ust-elf.h"
ddabe860	23	#include "ust-helper.h"
405be658 MD	24
405be658 MD	25	#define BUF_LEN 4096
8e2aed3f	26
2df586a6 PP	27	#ifndef NT_GNU_BUILD_ID
	28	# define NT_GNU_BUILD_ID 3
	29	#endif
	30
8e2aed3f AB	31	/*
	32	* Retrieve the nth (where n is the `index` argument) phdr (program
	33	* header) from the given elf instance.
	34	*
	35	* A pointer to the phdr is returned on success, NULL on failure.
	36	*/
	37	static
	38	struct lttng_ust_elf_phdr lttng_ust_elf_get_phdr(struct lttng_ust_elf elf,
	39	uint16_t index)
	40	{
	41	struct lttng_ust_elf_phdr *phdr = NULL;
f5a6717a	42	off_t offset;
8e2aed3f AB	43
	44	if (!elf) {
	45	goto error;
	46	}
	47
	48	if (index >= elf->ehdr->e_phnum) {
	49	goto error;
	50	}
	51
	52	phdr = zmalloc(sizeof(struct lttng_ust_elf_phdr));
	53	if (!phdr) {
	54	goto error;
	55	}
	56
f5a6717a MD	57	offset = (off_t) elf->ehdr->e_phoff
f5a6717a MD	58	+ (off_t) index * elf->ehdr->e_phentsize;
405be658	59	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	60	goto error;
	61	}
	62
	63	if (is_elf_32_bit(elf)) {
	64	Elf32_Phdr elf_phdr;
	65
405be658 MD	66	if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
405be658 MD	67	< sizeof(elf_phdr)) {
8e2aed3f AB	68	goto error;
	69	}
	70	if (!is_elf_native_endian(elf)) {
	71	bswap_phdr(elf_phdr);
	72	}
	73	copy_phdr(elf_phdr, *phdr);
	74	} else {
	75	Elf64_Phdr elf_phdr;
	76
405be658 MD	77	if (lttng_ust_read(elf->fd, &elf_phdr, sizeof(elf_phdr))
405be658 MD	78	< sizeof(elf_phdr)) {
8e2aed3f AB	79	goto error;
	80	}
	81	if (!is_elf_native_endian(elf)) {
	82	bswap_phdr(elf_phdr);
	83	}
	84	copy_phdr(elf_phdr, *phdr);
	85	}
	86
	87	return phdr;
	88
	89	error:
	90	free(phdr);
	91	return NULL;
	92	}
	93
	94	/*
	95	* Retrieve the nth (where n is the `index` argument) shdr (section
	96	* header) from the given elf instance.
	97	*
	98	* A pointer to the shdr is returned on success, NULL on failure.
	99	*/
	100	static
	101	struct lttng_ust_elf_shdr lttng_ust_elf_get_shdr(struct lttng_ust_elf elf,
	102	uint16_t index)
	103	{
	104	struct lttng_ust_elf_shdr *shdr = NULL;
4c5dac0d	105	off_t offset;
8e2aed3f AB	106
	107	if (!elf) {
	108	goto error;
	109	}
	110
	111	if (index >= elf->ehdr->e_shnum) {
	112	goto error;
	113	}
	114
	115	shdr = zmalloc(sizeof(struct lttng_ust_elf_shdr));
	116	if (!shdr) {
	117	goto error;
	118	}
	119
4c5dac0d	120	offset = (off_t) elf->ehdr->e_shoff
5a26ac54	121	+ (off_t) index * elf->ehdr->e_shentsize;
405be658	122	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	123	goto error;
	124	}
	125
	126	if (is_elf_32_bit(elf)) {
	127	Elf32_Shdr elf_shdr;
	128
405be658 MD	129	if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
405be658 MD	130	< sizeof(elf_shdr)) {
8e2aed3f AB	131	goto error;
	132	}
	133	if (!is_elf_native_endian(elf)) {
	134	bswap_shdr(elf_shdr);
	135	}
	136	copy_shdr(elf_shdr, *shdr);
	137	} else {
	138	Elf64_Shdr elf_shdr;
	139
405be658 MD	140	if (lttng_ust_read(elf->fd, &elf_shdr, sizeof(elf_shdr))
405be658 MD	141	< sizeof(elf_shdr)) {
8e2aed3f AB	142	goto error;
	143	}
	144	if (!is_elf_native_endian(elf)) {
	145	bswap_shdr(elf_shdr);
	146	}
	147	copy_shdr(elf_shdr, *shdr);
	148	}
	149
	150	return shdr;
	151
	152	error:
	153	free(shdr);
	154	return NULL;
	155	}
	156
	157	/*
	158	* Lookup a section's name from a given offset (usually from an shdr's
	159	* sh_name value) in bytes relative to the beginning of the section
	160	* names string table.
	161	*
	162	* If no name is found, NULL is returned.
	163	*/
	164	static
f5a6717a	165	char lttng_ust_elf_get_section_name(struct lttng_ust_elf elf, off_t offset)
8e2aed3f AB	166	{
8e2aed3f AB	167	char *name = NULL;
405be658	168	size_t len = 0, to_read; /* len does not include \0 */
8e2aed3f AB	169
	170	if (!elf) {
	171	goto error;
	172	}
	173
	174	if (offset >= elf->section_names_size) {
	175	goto error;
	176	}
	177
405be658	178	if (lseek(elf->fd, elf->section_names_offset + offset, SEEK_SET) < 0) {
8e2aed3f AB	179	goto error;
8e2aed3f AB	180	}
405be658 MD	181
	182	to_read = elf->section_names_size - offset;
	183
	184	/* Find first \0 after or at current location, remember len. */
	185	for (;;) {
	186	char buf[BUF_LEN];
	187	ssize_t read_len;
	188	size_t i;
	189
	190	if (!to_read) {
8e2aed3f	191	goto error;
8e2aed3f	192	}
405be658 MD	193	read_len = lttng_ust_read(elf->fd, buf,
	194	min_t(size_t, BUF_LEN, to_read));
	195	if (read_len <= 0) {
	196	goto error;
	197	}
	198	for (i = 0; i < read_len; i++) {
	199	if (buf[i] == '\0') {
	200	len += i;
	201	goto end;
	202	}
	203	}
	204	len += read_len;
	205	to_read -= read_len;
8e2aed3f	206	}
8e2aed3f	207	end:
405be658	208	name = zmalloc(sizeof(char) * (len + 1)); /* + 1 for \0 */
8e2aed3f AB	209	if (!name) {
	210	goto error;
	211	}
405be658 MD	212	if (lseek(elf->fd, elf->section_names_offset + offset,
405be658 MD	213	SEEK_SET) < 0) {
8e2aed3f AB	214	goto error;
8e2aed3f AB	215	}
405be658	216	if (lttng_ust_read(elf->fd, name, len + 1) < len + 1) {
8e2aed3f AB	217	goto error;
	218	}
	219
	220	return name;
	221
	222	error:
	223	free(name);
	224	return NULL;
	225	}
	226
	227	/*
	228	* Create an instance of lttng_ust_elf for the ELF file located at
	229	* `path`.
	230	*
	231	* Return a pointer to the instance on success, NULL on failure.
	232	*/
	233	struct lttng_ust_elf lttng_ust_elf_create(const char path)
	234	{
	235	uint8_t e_ident[EI_NIDENT];
	236	struct lttng_ust_elf_shdr *section_names_shdr;
405be658	237	struct lttng_ust_elf *elf = NULL;
f5c453e9	238	int ret, fd;
8e2aed3f AB	239
	240	elf = zmalloc(sizeof(struct lttng_ust_elf));
	241	if (!elf) {
	242	goto error;
	243	}
	244
1ac2e79c JR	245	/* Initialize fd field to -1. 0 is a valid fd number */
1ac2e79c JR	246	elf->fd = -1;
ba8dcc8c	247
8e2aed3f AB	248	elf->path = strdup(path);
	249	if (!elf->path) {
	250	goto error;
	251	}
	252
ba8dcc8c	253	lttng_ust_lock_fd_tracker();
f5c453e9 JR	254	fd = open(elf->path, O_RDONLY \| O_CLOEXEC);
f5c453e9 JR	255	if (fd < 0) {
ba8dcc8c	256	lttng_ust_unlock_fd_tracker();
8e2aed3f AB	257	goto error;
8e2aed3f AB	258	}
f5c453e9 JR	259
	260	ret = lttng_ust_add_fd_to_tracker(fd);
	261	if (ret < 0) {
	262	ret = close(fd);
	263	if (ret) {
	264	PERROR("close on elf->fd");
	265	}
	266	ret = -1;
	267	lttng_ust_unlock_fd_tracker();
	268	goto error;
	269	}
	270	elf->fd = ret;
ba8dcc8c	271	lttng_ust_unlock_fd_tracker();
8e2aed3f	272
405be658	273	if (lttng_ust_read(elf->fd, e_ident, EI_NIDENT) < EI_NIDENT) {
8e2aed3f AB	274	goto error;
	275	}
	276	elf->bitness = e_ident[EI_CLASS];
	277	elf->endianness = e_ident[EI_DATA];
405be658 MD	278
	279	if (lseek(elf->fd, 0, SEEK_SET) < 0) {
	280	goto error;
	281	}
8e2aed3f AB	282
	283	elf->ehdr = zmalloc(sizeof(struct lttng_ust_elf_ehdr));
	284	if (!elf->ehdr) {
	285	goto error;
	286	}
	287
	288	if (is_elf_32_bit(elf)) {
	289	Elf32_Ehdr elf_ehdr;
	290
405be658 MD	291	if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
405be658 MD	292	< sizeof(elf_ehdr)) {
8e2aed3f AB	293	goto error;
	294	}
	295	if (!is_elf_native_endian(elf)) {
	296	bswap_ehdr(elf_ehdr);
	297	}
	298	copy_ehdr(elf_ehdr, *(elf->ehdr));
	299	} else {
	300	Elf64_Ehdr elf_ehdr;
	301
405be658 MD	302	if (lttng_ust_read(elf->fd, &elf_ehdr, sizeof(elf_ehdr))
405be658 MD	303	< sizeof(elf_ehdr)) {
8e2aed3f AB	304	goto error;
	305	}
	306	if (!is_elf_native_endian(elf)) {
	307	bswap_ehdr(elf_ehdr);
	308	}
	309	copy_ehdr(elf_ehdr, *(elf->ehdr));
	310	}
	311
	312	section_names_shdr = lttng_ust_elf_get_shdr(elf, elf->ehdr->e_shstrndx);
	313	if (!section_names_shdr) {
	314	goto error;
	315	}
	316
	317	elf->section_names_offset = section_names_shdr->sh_offset;
	318	elf->section_names_size = section_names_shdr->sh_size;
	319
	320	free(section_names_shdr);
8e2aed3f AB	321	return elf;
	322
	323	error:
ba8dcc8c	324	lttng_ust_elf_destroy(elf);
8e2aed3f AB	325	return NULL;
	326	}
	327
f5eb039d AB	328	/*
	329	* Test whether the ELF file is position independent code (PIC)
	330	*/
	331	uint8_t lttng_ust_elf_is_pic(struct lttng_ust_elf *elf)
	332	{
	333	/*
	334	* PIC has and e_type value of ET_DYN, see ELF specification
	335	* version 1.1 p. 1-3.
	336	*/
	337	return elf->ehdr->e_type == ET_DYN;
	338	}
	339
8e2aed3f AB	340	/*
	341	* Destroy the given lttng_ust_elf instance.
	342	*/
	343	void lttng_ust_elf_destroy(struct lttng_ust_elf *elf)
	344	{
ba8dcc8c JR	345	int ret;
ba8dcc8c JR	346
8e2aed3f AB	347	if (!elf) {
	348	return;
	349	}
	350
ba8dcc8c JR	351	if (elf->fd >= 0) {
	352	lttng_ust_lock_fd_tracker();
	353	ret = close(elf->fd);
	354	if (!ret) {
	355	lttng_ust_delete_fd_from_tracker(elf->fd);
	356	} else {
	357	PERROR("close");
	358	abort();
	359	}
	360	lttng_ust_unlock_fd_tracker();
405be658	361	}
ba8dcc8c JR	362
ba8dcc8c JR	363	free(elf->ehdr);
8e2aed3f AB	364	free(elf->path);
	365	free(elf);
	366	}
	367
	368	/*
	369	* Compute the total in-memory size of the ELF file, in bytes.
	370	*
	371	* Returns 0 if successful, -1 if not. On success, the memory size is
	372	* returned through the out parameter `memsz`.
	373	*/
	374	int lttng_ust_elf_get_memsz(struct lttng_ust_elf elf, uint64_t memsz)
	375	{
	376	uint16_t i;
e1f0c569	377	uint64_t low_addr = UINT64_MAX, high_addr = 0;
8e2aed3f AB	378
	379	if (!elf \|\| !memsz) {
	380	goto error;
	381	}
	382
	383	for (i = 0; i < elf->ehdr->e_phnum; ++i) {
	384	struct lttng_ust_elf_phdr *phdr;
8e2aed3f AB	385
	386	phdr = lttng_ust_elf_get_phdr(elf, i);
	387	if (!phdr) {
	388	goto error;
	389	}
	390
	391	/*
	392	* Only PT_LOAD segments contribute to memsz. Skip
	393	* other segments.
	394	*/
	395	if (phdr->p_type != PT_LOAD) {
	396	goto next_loop;
	397	}
	398
8886accb MD	399	low_addr = min_t(uint64_t, low_addr, phdr->p_vaddr);
	400	high_addr = max_t(uint64_t, high_addr,
	401	phdr->p_vaddr + phdr->p_memsz);
8e2aed3f AB	402	next_loop:
	403	free(phdr);
	404	}
	405
e1f0c569 AB	406	if (high_addr < low_addr) {
	407	/* No PT_LOAD segments or corrupted data. */
	408	goto error;
	409	}
	410
	411	*memsz = high_addr - low_addr;
8e2aed3f AB	412	return 0;
	413	error:
	414	return -1;
	415	}
	416
	417	/*
	418	* Internal method used to try and get the build_id from a PT_NOTE
	419	* segment ranging from `offset` to `segment_end`.
	420	*
	421	* If the function returns successfully, the out parameter `found`
	422	* indicates whether the build id information was present in the
	423	* segment or not. If `found` is not 0, the out parameters `build_id`
	424	* and `length` will both have been set with the retrieved
	425	* information.
	426	*
	427	* Returns 0 on success, -1 if an error occurred.
	428	*/
	429	static
	430	int lttng_ust_elf_get_build_id_from_segment(
	431	struct lttng_ust_elf elf, uint8_t build_id, size_t length,
82ee1ee4	432	off_t offset, off_t segment_end)
8e2aed3f	433	{
814d07b1 MD	434	uint8_t _build_id = NULL; / Silence old gcc warning. */
814d07b1 MD	435	size_t _length = 0; /* Silence old gcc warning. */
8e2aed3f AB	436
	437	while (offset < segment_end) {
	438	struct lttng_ust_elf_nhdr nhdr;
405be658	439	size_t read_len;
8e2aed3f AB	440
8e2aed3f AB	441	/* Align start of note entry */
b72687b8	442	offset += lttng_ust_offset_align(offset, ELF_NOTE_ENTRY_ALIGN);
8e2aed3f AB	443	if (offset >= segment_end) {
	444	break;
	445	}
	446	/*
	447	* We seek manually because if the note isn't the
	448	* build id the data following the header will not
	449	* have been read.
	450	*/
405be658	451	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	452	goto error;
8e2aed3f AB	453	}
405be658 MD	454	if (lttng_ust_read(elf->fd, &nhdr, sizeof(nhdr))
405be658 MD	455	< sizeof(nhdr)) {
8e2aed3f AB	456	goto error;
	457	}
	458
	459	if (!is_elf_native_endian(elf)) {
	460	nhdr.n_namesz = bswap_32(nhdr.n_namesz);
	461	nhdr.n_descsz = bswap_32(nhdr.n_descsz);
	462	nhdr.n_type = bswap_32(nhdr.n_type);
	463	}
	464
	465	offset += sizeof(nhdr) + nhdr.n_namesz;
	466	/* Align start of desc entry */
b72687b8	467	offset += lttng_ust_offset_align(offset, ELF_NOTE_DESC_ALIGN);
8e2aed3f AB	468
	469	if (nhdr.n_type != NT_GNU_BUILD_ID) {
	470	/*
	471	* Ignore non build id notes but still
	472	* increase the offset.
	473	*/
	474	offset += nhdr.n_descsz;
	475	continue;
	476	}
	477
	478	_length = nhdr.n_descsz;
	479	_build_id = zmalloc(sizeof(uint8_t) * _length);
5ada26b4	480	if (!_build_id) {
8e2aed3f AB	481	goto error;
	482	}
	483
405be658	484	if (lseek(elf->fd, offset, SEEK_SET) < 0) {
8e2aed3f AB	485	goto error;
8e2aed3f AB	486	}
405be658 MD	487	read_len = sizeof(_build_id) _length;
405be658 MD	488	if (lttng_ust_read(elf->fd, _build_id, read_len) < read_len) {
8e2aed3f AB	489	goto error;
	490	}
	491
8e2aed3f AB	492	break;
	493	}
	494
82ee1ee4	495	if (_build_id) {
8e2aed3f AB	496	*build_id = _build_id;
	497	*length = _length;
	498	}
	499
8e2aed3f AB	500	return 0;
8e2aed3f AB	501	error:
83215d66	502	free(_build_id);
8e2aed3f AB	503	return -1;
	504	}
	505
	506	/*
	507	* Retrieve a build ID (an array of bytes) from the corresponding
	508	* section in the ELF file. The length of the build ID can be either
	509	* 16 or 20 bytes depending on the method used to generate it, hence
	510	* the length out parameter.
	511	*
	512	* If the function returns successfully, the out parameter `found`
	513	* indicates whether the build id information was present in the ELF
	514	* file or not. If `found` is not 0, the out parameters `build_id` and
	515	* `length` will both have been set with the retrieved information.
	516	*
	517	* Returns 0 on success, -1 if an error occurred.
	518	*/
	519	int lttng_ust_elf_get_build_id(struct lttng_ust_elf elf, uint8_t *build_id,
	520	size_t length, int found)
	521	{
	522	uint16_t i;
8c83dbda MD	523	uint8_t _build_id = NULL; / Silence old gcc warning. */
8c83dbda MD	524	size_t _length = 0; /* Silence old gcc warning. */
8e2aed3f AB	525
	526	if (!elf \|\| !build_id \|\| !length \|\| !found) {
	527	goto error;
	528	}
	529
	530	for (i = 0; i < elf->ehdr->e_phnum; ++i) {
f5a6717a	531	off_t offset, segment_end;
8e2aed3f	532	struct lttng_ust_elf_phdr *phdr;
5b3bbf98	533	int ret = 0;
8e2aed3f AB	534
	535	phdr = lttng_ust_elf_get_phdr(elf, i);
	536	if (!phdr) {
	537	goto error;
	538	}
	539
	540	/* Build ID will be contained in a PT_NOTE segment. */
	541	if (phdr->p_type != PT_NOTE) {
	542	goto next_loop;
	543	}
	544
	545	offset = phdr->p_offset;
	546	segment_end = offset + phdr->p_filesz;
	547	ret = lttng_ust_elf_get_build_id_from_segment(
82ee1ee4	548	elf, &_build_id, &_length, offset, segment_end);
8e2aed3f AB	549	next_loop:
	550	free(phdr);
	551	if (ret) {
	552	goto error;
	553	}
82ee1ee4	554	if (_build_id) {
8e2aed3f AB	555	break;
	556	}
	557	}
	558
82ee1ee4	559	if (_build_id) {
8e2aed3f AB	560	*build_id = _build_id;
8e2aed3f AB	561	*length = _length;
82ee1ee4 AB	562	*found = 1;
	563	} else {
	564	*found = 0;
8e2aed3f AB	565	}
8e2aed3f AB	566
8e2aed3f AB	567	return 0;
8e2aed3f AB	568	error:
99b7132d	569	free(_build_id);
8e2aed3f AB	570	return -1;
	571	}
	572
	573	/*
	574	* Try to retrieve filename and CRC from given ELF section `shdr`.
	575	*
	576	* If the function returns successfully, the out parameter `found`
	577	* indicates whether the debug link information was present in the ELF
	578	* section or not. If `found` is not 0, the out parameters `filename` and
	579	* `crc` will both have been set with the retrieved information.
	580	*
	581	* Returns 0 on success, -1 if an error occurred.
	582	*/
4b4a1337	583	static
8e2aed3f AB	584	int lttng_ust_elf_get_debug_link_from_section(struct lttng_ust_elf *elf,
8e2aed3f AB	585	char *filename, uint32_t crc,
8e2aed3f AB	586	struct lttng_ust_elf_shdr *shdr)
8e2aed3f AB	587	{
8c83dbda	588	char _filename = NULL; / Silence old gcc warning. */
405be658	589	size_t filename_len;
8e2aed3f	590	char *section_name = NULL;
8c83dbda	591	uint32_t _crc = 0; /* Silence old gcc warning. */
8e2aed3f	592
82ee1ee4	593	if (!elf \|\| !filename \|\| !crc \|\| !shdr) {
8e2aed3f AB	594	goto error;
	595	}
	596
	597	/*
	598	* The .gnu_debuglink section is of type SHT_PROGBITS,
	599	* skip the other sections.
	600	*/
	601	if (shdr->sh_type != SHT_PROGBITS) {
	602	goto end;
	603	}
	604
	605	section_name = lttng_ust_elf_get_section_name(elf,
	606	shdr->sh_name);
	607	if (!section_name) {
	608	goto end;
	609	}
	610	if (strcmp(section_name, ".gnu_debuglink")) {
	611	goto end;
	612	}
	613
	614	/*
	615	* The length of the filename is the sh_size excluding the CRC
	616	* which comes after it in the section.
	617	*/
	618	_filename = zmalloc(sizeof(char) * (shdr->sh_size - ELF_CRC_SIZE));
	619	if (!_filename) {
	620	goto error;
	621	}
405be658	622	if (lseek(elf->fd, shdr->sh_offset, SEEK_SET) < 0) {
8e2aed3f AB	623	goto error;
8e2aed3f AB	624	}
405be658 MD	625	filename_len = sizeof(_filename) (shdr->sh_size - ELF_CRC_SIZE);
405be658 MD	626	if (lttng_ust_read(elf->fd, _filename, filename_len) < filename_len) {
8e2aed3f AB	627	goto error;
8e2aed3f AB	628	}
405be658	629	if (lttng_ust_read(elf->fd, &_crc, sizeof(_crc)) < sizeof(_crc)) {
8e2aed3f AB	630	goto error;
	631	}
	632	if (!is_elf_native_endian(elf)) {
	633	_crc = bswap_32(_crc);
	634	}
	635
8e2aed3f AB	636	end:
8e2aed3f AB	637	free(section_name);
82ee1ee4	638	if (_filename) {
8e2aed3f AB	639	*filename = _filename;
	640	*crc = _crc;
	641	}
8e2aed3f AB	642
	643	return 0;
	644
	645	error:
83215d66 MD	646	free(_filename);
83215d66 MD	647	free(section_name);
8e2aed3f AB	648	return -1;
	649	}
	650
	651	/*
	652	* Retrieve filename and CRC from ELF's .gnu_debuglink section, if any.
	653	*
	654	* If the function returns successfully, the out parameter `found`
	655	* indicates whether the debug link information was present in the ELF
	656	* file or not. If `found` is not 0, the out parameters `filename` and
	657	* `crc` will both have been set with the retrieved information.
	658	*
	659	* Returns 0 on success, -1 if an error occurred.
	660	*/
	661	int lttng_ust_elf_get_debug_link(struct lttng_ust_elf elf, char *filename,
	662	uint32_t crc, int found)
	663	{
	664	int ret;
	665	uint16_t i;
8c83dbda MD	666	char _filename = NULL; / Silence old gcc warning. */
8c83dbda MD	667	uint32_t _crc = 0; /* Silence old gcc warning. */
8e2aed3f AB	668
	669	if (!elf \|\| !filename \|\| !crc \|\| !found) {
	670	goto error;
	671	}
	672
	673	for (i = 0; i < elf->ehdr->e_shnum; ++i) {
	674	struct lttng_ust_elf_shdr *shdr = NULL;
	675
	676	shdr = lttng_ust_elf_get_shdr(elf, i);
	677	if (!shdr) {
	678	goto error;
	679	}
	680
	681	ret = lttng_ust_elf_get_debug_link_from_section(
82ee1ee4	682	elf, &_filename, &_crc, shdr);
8e2aed3f AB	683	free(shdr);
	684
	685	if (ret) {
	686	goto error;
	687	}
82ee1ee4	688	if (_filename) {
8e2aed3f AB	689	break;
	690	}
	691	}
	692
82ee1ee4	693	if (_filename) {
8e2aed3f AB	694	*filename = _filename;
8e2aed3f AB	695	*crc = _crc;
82ee1ee4 AB	696	*found = 1;
	697	} else {
	698	*found = 0;
8e2aed3f AB	699	}
8e2aed3f AB	700
8e2aed3f	701	return 0;
82ee1ee4	702
8e2aed3f	703	error:
99b7132d	704	free(_filename);
8e2aed3f AB	705	return -1;
8e2aed3f AB	706	}