libdtrace/common/dt_link.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 * Copyright 2017-2018 Mark Johnston <markj@FreeBSD.org>
 */

#pragma ident	"%Z%%M%	%I%	%E% SMI"

#define	ELF_TARGET_ALL
#include <elf.h>

#include <sys/types.h>
#ifdef illumos
#include <sys/sysmacros.h>
#else
#define	P2ROUNDUP(x, align)		(-(-(x) & -(align)))
#endif

#include <unistd.h>
#include <strings.h>
#ifdef illumos
#include <alloca.h>
#endif
#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#ifdef illumos
#include <wait.h>
#else
#include <sys/wait.h>
#include <libelf.h>
#include <gelf.h>
#include <sys/mman.h>
#endif
#include <assert.h>
#include <sys/ipc.h>

#include <dt_impl.h>
#include <dt_provider.h>
#include <dt_program.h>
#include <dt_string.h>

#define	ESHDR_NULL	0
#define	ESHDR_SHSTRTAB	1
#define	ESHDR_DOF	2
#define	ESHDR_STRTAB	3
#define	ESHDR_SYMTAB	4
#define	ESHDR_REL	5
#define	ESHDR_NUM	6

#define	PWRITE_SCN(index, data) \
	(lseek64(fd, (off64_t)elf_file.shdr[(index)].sh_offset, SEEK_SET) != \
	(off64_t)elf_file.shdr[(index)].sh_offset || \
	dt_write(dtp, fd, (data), elf_file.shdr[(index)].sh_size) != \
	elf_file.shdr[(index)].sh_size)

static const char DTRACE_SHSTRTAB32[] = "\0"
".shstrtab\0"		/* 1 */
".SUNW_dof\0"		/* 11 */
".strtab\0"		/* 21 */
".symtab\0"		/* 29 */
#ifdef __sparc
".rela.SUNW_dof";	/* 37 */
#else
".rel.SUNW_dof";	/* 37 */
#endif

static const char DTRACE_SHSTRTAB64[] = "\0"
".shstrtab\0"		/* 1 */
".SUNW_dof\0"		/* 11 */
".strtab\0"		/* 21 */
".symtab\0"		/* 29 */
".rela.SUNW_dof";	/* 37 */

static const char DOFSTR[] = "__SUNW_dof";
static const char DOFLAZYSTR[] = "___SUNW_dof";

typedef struct dt_link_pair {
	struct dt_link_pair *dlp_next;	/* next pair in linked list */
	void *dlp_str;			/* buffer for string table */
	void *dlp_sym;			/* buffer for symbol table */
} dt_link_pair_t;

typedef struct dof_elf32 {
	uint32_t de_nrel;		/* relocation count */
#ifdef __sparc
	Elf32_Rela *de_rel;		/* array of relocations for sparc */
#else
	Elf32_Rel *de_rel;		/* array of relocations for x86 */
#endif
	uint32_t de_nsym;		/* symbol count */
	Elf32_Sym *de_sym;		/* array of symbols */
	uint32_t de_strlen;		/* size of of string table */
	char *de_strtab;		/* string table */
	uint32_t de_global;		/* index of the first global symbol */
} dof_elf32_t;

static int
prepare_elf32(dtrace_hdl_t *dtp, const dof_hdr_t *dof, dof_elf32_t *dep)
{
	dof_sec_t *dofs, *s;
	dof_relohdr_t *dofrh;
	dof_relodesc_t *dofr;
	char *strtab;
	int i, j, nrel;
	size_t strtabsz = 1;
	uint32_t count = 0;
	size_t base;
	Elf32_Sym *sym;
#ifdef __sparc
	Elf32_Rela *rel;
#else
	Elf32_Rel *rel;
#endif

	/*LINTED*/
	dofs = (dof_sec_t *)((char *)dof + dof->dofh_secoff);

	/*
	 * First compute the size of the string table and the number of
	 * relocations present in the DOF.
	 */
	for (i = 0; i < dof->dofh_secnum; i++) {
		if (dofs[i].dofs_type != DOF_SECT_URELHDR)
			continue;

		/*LINTED*/
		dofrh = (dof_relohdr_t *)((char *)dof + dofs[i].dofs_offset);

		s = &dofs[dofrh->dofr_strtab];
		strtab = (char *)dof + s->dofs_offset;
		assert(strtab[0] == '\0');
		strtabsz += s->dofs_size - 1;

		s = &dofs[dofrh->dofr_relsec];
		/*LINTED*/
		dofr = (dof_relodesc_t *)((char *)dof + s->dofs_offset);
		count += s->dofs_size / s->dofs_entsize;
	}

	dep->de_strlen = strtabsz;
	dep->de_nrel = count;
	dep->de_nsym = count + 1; /* the first symbol is always null */

	if (dtp->dt_lazyload) {
		dep->de_strlen += sizeof (DOFLAZYSTR);
		dep->de_nsym++;
	} else {
		dep->de_strlen += sizeof (DOFSTR);
		dep->de_nsym++;
	}

	if ((dep->de_rel = calloc(dep->de_nrel,
	    sizeof (dep->de_rel[0]))) == NULL) {
		return (dt_set_errno(dtp, EDT_NOMEM));
	}

	if ((dep->de_sym = calloc(dep->de_nsym, sizeof (Elf32_Sym))) == NULL) {
		free(dep->de_rel);
		return (dt_set_errno(dtp, EDT_NOMEM));
	}

	if ((dep->de_strtab = calloc(dep->de_strlen, 1)) == NULL) {
		free(dep->de_rel);
		free(dep->de_sym);
		return (dt_set_errno(dtp, EDT_NOMEM));
	}

	count = 0;
	strtabsz = 1;
	dep->de_strtab[0] = '\0';
	rel = dep->de_rel;
	sym = dep->de_sym;
	dep->de_global = 1;

	/*
	 * The first symbol table entry must be zeroed and is always ignored.
	 */
	bzero(sym, sizeof (Elf32_Sym));
	sym++;

	/*
	 * Take a second pass through the DOF sections filling in the
	 * memory we allocated.
	 */
	for (i = 0; i < dof->dofh_secnum; i++) {
		if (dofs[i].dofs_type != DOF_SECT_URELHDR)
			continue;

		/*LINTED*/
		dofrh = (dof_relohdr_t *)((char *)dof + dofs[i].dofs_offset);

		s = &dofs[dofrh->dofr_strtab];
		strtab = (char *)dof + s->dofs_offset;
		bcopy(strtab + 1, dep->de_strtab + strtabsz, s->dofs_size);
		base = strtabsz;
		strtabsz += s->dofs_size - 1;

		s = &dofs[dofrh->dofr_relsec];
		/*LINTED*/
		dofr = (dof_relodesc_t *)((char *)dof + s->dofs_offset);
		nrel = s->dofs_size / s->dofs_entsize;

		s = &dofs[dofrh->dofr_tgtsec];

		for (j = 0; j < nrel; j++) {
#if defined(__aarch64__)
			rel->r_offset = s->dofs_offset +
			    dofr[j].dofr_offset;
			rel->r_info = ELF32_R_INFO(count + dep->de_global,
			    R_ARM_REL32);
#elif defined(__arm__)
/* XXX */
			printf("%s:%s(%d): arm not implemented\n",
			    __FUNCTION__, __FILE__, __LINE__);
#elif defined(__i386) || defined(__amd64)
			rel->r_offset = s->dofs_offset +
			    dofr[j].dofr_offset;
			rel->r_info = ELF32_R_INFO(count + dep->de_global,
			    R_386_PC32);
#elif defined(__mips__)
/* XXX */
			printf("%s:%s(%d): MIPS not implemented\n",
			    __FUNCTION__, __FILE__, __LINE__);
#elif defined(__powerpc__)
			/*
			 * Add 4 bytes to hit the low half of this 64-bit
			 * big-endian address.
			 */
			rel->r_offset = s->dofs_offset +
			    dofr[j].dofr_offset + 4;
			rel->r_info = ELF32_R_INFO(count + dep->de_global,
			    R_PPC_REL32);
#elif defined(__riscv)
/* XXX */
			printf("%s:%s(%d): RISC-V not implemented\n",
			    __FUNCTION__, __FILE__, __LINE__);
#else
#error unknown ISA
#endif

			sym->st_name = base + dofr[j].dofr_name - 1;
			sym->st_value = 0;
			sym->st_size = 0;
			sym->st_info = ELF32_ST_INFO(STB_GLOBAL, STT_FUNC);
			sym->st_other = ELF32_ST_VISIBILITY(STV_HIDDEN);
			sym->st_shndx = SHN_UNDEF;

			rel++;
			sym++;
			count++;
		}
	}

	/*
	 * Add a symbol for the DOF itself. We use a different symbol for
	 * lazily and actively loaded DOF to make them easy to distinguish.
	 */
	sym->st_name = strtabsz;
	sym->st_value = 0;
	sym->st_size = dof->dofh_filesz;
	sym->st_info = ELF32_ST_INFO(STB_GLOBAL, STT_OBJECT);
	sym->st_other = ELF32_ST_VISIBILITY(STV_HIDDEN);
	sym->st_shndx = ESHDR_DOF;
	sym++;

	if (dtp->dt_lazyload) {
		bcopy(DOFLAZYSTR, dep->de_strtab + strtabsz,
		    sizeof (DOFLAZYSTR));
		strtabsz += sizeof (DOFLAZYSTR);
	} else {
		bcopy(DOFSTR, dep->de_strtab + strtabsz, sizeof (DOFSTR));
		strtabsz += sizeof (DOFSTR);
	}

	assert(count == dep->de_nrel);
	assert(strtabsz == dep->de_strlen);

	return (0);
}


typedef struct dof_elf64 {
	uint32_t de_nrel;
	Elf64_Rela *de_rel;
	uint32_t de_nsym;
	Elf64_Sym *de_sym;

	uint32_t de_strlen;
	char *de_strtab;

	uint32_t de_global;
} dof_elf64_t;

static int
prepare_elf64(dtrace_hdl_t *dtp, const dof_hdr_t *dof, dof_elf64_t *dep)
{
	dof_sec_t *dofs, *s;
	dof_relohdr_t *dofrh;
	dof_relodesc_t *dofr;
	char *strtab;
	int i, j, nrel;
	size_t strtabsz = 1;
#ifdef illumos
	uint32_t count = 0;
#else
	uint64_t count = 0;
#endif
	size_t base;
	Elf64_Sym *sym;
	Elf64_Rela *rel;

	/*LINTED*/
	dofs = (dof_sec_t *)((char *)dof + dof->dofh_secoff);

	/*
	 * First compute the size of the string table and the number of
	 * relocations present in the DOF.
	 */
	for (i = 0; i < dof->dofh_secnum; i++) {
		if (dofs[i].dofs_type != DOF_SECT_URELHDR)
			continue;

		/*LINTED*/
		dofrh = (dof_relohdr_t *)((char *)dof + dofs[i].dofs_offset);

		s = &dofs[dofrh->dofr_strtab];
		strtab = (char *)dof + s->dofs_offset;
		assert(strtab[0] == '\0');
		strtabsz += s->dofs_size - 1;

		s = &dofs[dofrh->dofr_relsec];
		/*LINTED*/
		dofr = (dof_relodesc_t *)((char *)dof + s->dofs_offset);
		count += s->dofs_size / s->dofs_entsize;
	}

	dep->de_strlen = strtabsz;
	dep->de_nrel = count;
	dep->de_nsym = count + 1; /* the first symbol is always null */

	if (dtp->dt_lazyload) {
		dep->de_strlen += sizeof (DOFLAZYSTR);
		dep->de_nsym++;
	} else {
		dep->de_strlen += sizeof (DOFSTR);
		dep->de_nsym++;
	}

	if ((dep->de_rel = calloc(dep->de_nrel,
	    sizeof (dep->de_rel[0]))) == NULL) {
		return (dt_set_errno(dtp, EDT_NOMEM));
	}

	if ((dep->de_sym = calloc(dep->de_nsym, sizeof (Elf64_Sym))) == NULL) {
		free(dep->de_rel);
		return (dt_set_errno(dtp, EDT_NOMEM));
	}

	if ((dep->de_strtab = calloc(dep->de_strlen, 1)) == NULL) {
		free(dep->de_rel);
		free(dep->de_sym);
		return (dt_set_errno(dtp, EDT_NOMEM));
	}

	count = 0;
	strtabsz = 1;
	dep->de_strtab[0] = '\0';
	rel = dep->de_rel;
	sym = dep->de_sym;
	dep->de_global = 1;

	/*
	 * The first symbol table entry must be zeroed and is always ignored.
	 */
	bzero(sym, sizeof (Elf64_Sym));
	sym++;

	/*
	 * Take a second pass through the DOF sections filling in the
	 * memory we allocated.
	 */
	for (i = 0; i < dof->dofh_secnum; i++) {
		if (dofs[i].dofs_type != DOF_SECT_URELHDR)
			continue;

		/*LINTED*/
		dofrh = (dof_relohdr_t *)((char *)dof + dofs[i].dofs_offset);

		s = &dofs[dofrh->dofr_strtab];
		strtab = (char *)dof + s->dofs_offset;
		bcopy(strtab + 1, dep->de_strtab + strtabsz, s->dofs_size);
		base = strtabsz;
		strtabsz += s->dofs_size - 1;

		s = &dofs[dofrh->dofr_relsec];
		/*LINTED*/
		dofr = (dof_relodesc_t *)((char *)dof + s->dofs_offset);
		nrel = s->dofs_size / s->dofs_entsize;

		s = &dofs[dofrh->dofr_tgtsec];

		for (j = 0; j < nrel; j++) {
#if defined(__aarch64__)
			rel->r_offset = s->dofs_offset +
			    dofr[j].dofr_offset;
			rel->r_info = ELF64_R_INFO(count + dep->de_global,
			    R_AARCH64_PREL64);
#elif defined(__arm__)
/* XXX */
#elif defined(__mips__)
/* XXX */
#elif defined(__powerpc__)
			rel->r_offset = s->dofs_offset +
			    dofr[j].dofr_offset;
			rel->r_info = ELF64_R_INFO(count + dep->de_global,
			    R_PPC64_REL64);
#elif defined(__riscv)
/* XXX */
#elif defined(__i386) || defined(__amd64)
			rel->r_offset = s->dofs_offset +
			    dofr[j].dofr_offset;
			rel->r_info = ELF64_R_INFO(count + dep->de_global,
			    R_X86_64_PC64);
#else
#error unknown ISA
#endif

			sym->st_name = base + dofr[j].dofr_name - 1;
			sym->st_value = 0;
			sym->st_size = 0;
			sym->st_info = GELF_ST_INFO(STB_GLOBAL, STT_FUNC);
			sym->st_other = ELF64_ST_VISIBILITY(STV_HIDDEN);
			sym->st_shndx = SHN_UNDEF;

			rel++;
			sym++;
			count++;
		}
	}

	/*
	 * Add a symbol for the DOF itself. We use a different symbol for
	 * lazily and actively loaded DOF to make them easy to distinguish.
	 */
	sym->st_name = strtabsz;
	sym->st_value = 0;
	sym->st_size = dof->dofh_filesz;
	sym->st_info = GELF_ST_INFO(STB_GLOBAL, STT_OBJECT);
	sym->st_other = ELF64_ST_VISIBILITY(STV_HIDDEN);
	sym->st_shndx = ESHDR_DOF;
	sym++;

	if (dtp->dt_lazyload) {
		bcopy(DOFLAZYSTR, dep->de_strtab + strtabsz,
		    sizeof (DOFLAZYSTR));
		strtabsz += sizeof (DOFLAZYSTR);
	} else {
		bcopy(DOFSTR, dep->de_strtab + strtabsz, sizeof (DOFSTR));
		strtabsz += sizeof (DOFSTR);
	}

	assert(count == dep->de_nrel);
	assert(strtabsz == dep->de_strlen);

	return (0);
}

/*
 * Write out an ELF32 file prologue consisting of a header, section headers,
 * and a section header string table.  The DOF data will follow this prologue
 * and complete the contents of the given ELF file.
 */
static int
dump_elf32(dtrace_hdl_t *dtp, const dof_hdr_t *dof, int fd)
{
	struct {
		Elf32_Ehdr ehdr;
		Elf32_Shdr shdr[ESHDR_NUM];
	} elf_file;

	Elf32_Shdr *shp;
	Elf32_Off off;
	dof_elf32_t de;
	int ret = 0;
	uint_t nshdr;

	if (prepare_elf32(dtp, dof, &de) != 0)
		return (-1); /* errno is set for us */

	/*
	 * If there are no relocations, we only need enough sections for
	 * the shstrtab and the DOF.
	 */
	nshdr = de.de_nrel == 0 ? ESHDR_SYMTAB + 1 : ESHDR_NUM;

	bzero(&elf_file, sizeof (elf_file));

	elf_file.ehdr.e_ident[EI_MAG0] = ELFMAG0;
	elf_file.ehdr.e_ident[EI_MAG1] = ELFMAG1;
	elf_file.ehdr.e_ident[EI_MAG2] = ELFMAG2;
	elf_file.ehdr.e_ident[EI_MAG3] = ELFMAG3;
	elf_file.ehdr.e_ident[EI_VERSION] = EV_CURRENT;
	elf_file.ehdr.e_ident[EI_CLASS] = ELFCLASS32;
#if BYTE_ORDER == _BIG_ENDIAN
	elf_file.ehdr.e_ident[EI_DATA] = ELFDATA2MSB;
#else
	elf_file.ehdr.e_ident[EI_DATA] = ELFDATA2LSB;
#endif
#if defined(__FreeBSD__)
	elf_file.ehdr.e_ident[EI_OSABI] = ELFOSABI_FREEBSD;
#endif
	elf_file.ehdr.e_type = ET_REL;
#if defined(__arm__)
	elf_file.ehdr.e_machine = EM_ARM;
#elif defined(__mips__)
	elf_file.ehdr.e_machine = EM_MIPS;
#elif defined(__powerpc__)
	elf_file.ehdr.e_machine = EM_PPC;
#elif defined(__sparc)
	elf_file.ehdr.e_machine = EM_SPARC;
#elif defined(__i386) || defined(__amd64)
	elf_file.ehdr.e_machine = EM_386;
#elif defined(__aarch64__)
	elf_file.ehdr.e_machine = EM_AARCH64;
#endif
	elf_file.ehdr.e_version = EV_CURRENT;
	elf_file.ehdr.e_shoff = sizeof (Elf32_Ehdr);
	elf_file.ehdr.e_ehsize = sizeof (Elf32_Ehdr);
	elf_file.ehdr.e_phentsize = sizeof (Elf32_Phdr);
	elf_file.ehdr.e_shentsize = sizeof (Elf32_Shdr);
	elf_file.ehdr.e_shnum = nshdr;
	elf_file.ehdr.e_shstrndx = ESHDR_SHSTRTAB;
	off = sizeof (elf_file) + nshdr * sizeof (Elf32_Shdr);

	shp = &elf_file.shdr[ESHDR_SHSTRTAB];
	shp->sh_name = 1; /* DTRACE_SHSTRTAB32[1] = ".shstrtab" */
	shp->sh_type = SHT_STRTAB;
	shp->sh_offset = off;
	shp->sh_size = sizeof (DTRACE_SHSTRTAB32);
	shp->sh_addralign = sizeof (char);
	off = P2ROUNDUP(shp->sh_offset + shp->sh_size, 8);

	shp = &elf_file.shdr[ESHDR_DOF];
	shp->sh_name = 11; /* DTRACE_SHSTRTAB32[11] = ".SUNW_dof" */
	shp->sh_flags = SHF_ALLOC;
	shp->sh_type = SHT_SUNW_dof;
	shp->sh_offset = off;
	shp->sh_size = dof->dofh_filesz;
	shp->sh_addralign = 8;
	off = shp->sh_offset + shp->sh_size;

	shp = &elf_file.shdr[ESHDR_STRTAB];
	shp->sh_name = 21; /* DTRACE_SHSTRTAB32[21] = ".strtab" */
	shp->sh_flags = SHF_ALLOC;
	shp->sh_type = SHT_STRTAB;
	shp->sh_offset = off;
	shp->sh_size = de.de_strlen;
	shp->sh_addralign = sizeof (char);
	off = P2ROUNDUP(shp->sh_offset + shp->sh_size, 4);

	shp = &elf_file.shdr[ESHDR_SYMTAB];
	shp->sh_name = 29; /* DTRACE_SHSTRTAB32[29] = ".symtab" */
	shp->sh_flags = SHF_ALLOC;
	shp->sh_type = SHT_SYMTAB;
	shp->sh_entsize = sizeof (Elf32_Sym);
	shp->sh_link = ESHDR_STRTAB;
	shp->sh_offset = off;
	shp->sh_info = de.de_global;
	shp->sh_size = de.de_nsym * sizeof (Elf32_Sym);
	shp->sh_addralign = 4;
	off = P2ROUNDUP(shp->sh_offset + shp->sh_size, 4);

	if (de.de_nrel == 0) {
		if (dt_write(dtp, fd, &elf_file,
		    sizeof (elf_file)) != sizeof (elf_file) ||
		    PWRITE_SCN(ESHDR_SHSTRTAB, DTRACE_SHSTRTAB32) ||
		    PWRITE_SCN(ESHDR_STRTAB, de.de_strtab) ||
		    PWRITE_SCN(ESHDR_SYMTAB, de.de_sym) ||
		    PWRITE_SCN(ESHDR_DOF, dof)) {
			ret = dt_set_errno(dtp, errno);
		}
	} else {
		shp = &elf_file.shdr[ESHDR_REL];
		shp->sh_name = 37; /* DTRACE_SHSTRTAB32[37] = ".rel.SUNW_dof" */
		shp->sh_flags = SHF_ALLOC;
#ifdef __sparc
		shp->sh_type = SHT_RELA;
#else
		shp->sh_type = SHT_REL;
#endif
		shp->sh_entsize = sizeof (de.de_rel[0]);
		shp->sh_link = ESHDR_SYMTAB;
		shp->sh_info = ESHDR_DOF;
		shp->sh_offset = off;
		shp->sh_size = de.de_nrel * sizeof (de.de_rel[0]);
		shp->sh_addralign = 4;

		if (dt_write(dtp, fd, &elf_file,
		    sizeof (elf_file)) != sizeof (elf_file) ||
		    PWRITE_SCN(ESHDR_SHSTRTAB, DTRACE_SHSTRTAB32) ||
		    PWRITE_SCN(ESHDR_STRTAB, de.de_strtab) ||
		    PWRITE_SCN(ESHDR_SYMTAB, de.de_sym) ||
		    PWRITE_SCN(ESHDR_REL, de.de_rel) ||
		    PWRITE_SCN(ESHDR_DOF, dof)) {
			ret = dt_set_errno(dtp, errno);
		}
	}

	free(de.de_strtab);
	free(de.de_sym);
	free(de.de_rel);

	return (ret);
}

/*
 * Write out an ELF64 file prologue consisting of a header, section headers,
 * and a section header string table.  The DOF data will follow this prologue
 * and complete the contents of the given ELF file.
 */
static int
dump_elf64(dtrace_hdl_t *dtp, const dof_hdr_t *dof, int fd)
{
	struct {
		Elf64_Ehdr ehdr;
		Elf64_Shdr shdr[ESHDR_NUM];
	} elf_file;

	Elf64_Shdr *shp;
	Elf64_Off off;
	dof_elf64_t de;
	int ret = 0;
	uint_t nshdr;

	if (prepare_elf64(dtp, dof, &de) != 0)
		return (-1); /* errno is set for us */

	/*
	 * If there are no relocations, we only need enough sections for
	 * the shstrtab and the DOF.
	 */
	nshdr = de.de_nrel == 0 ? ESHDR_SYMTAB + 1 : ESHDR_NUM;

	bzero(&elf_file, sizeof (elf_file));

	elf_file.ehdr.e_ident[EI_MAG0] = ELFMAG0;
	elf_file.ehdr.e_ident[EI_MAG1] = ELFMAG1;
	elf_file.ehdr.e_ident[EI_MAG2] = ELFMAG2;
	elf_file.ehdr.e_ident[EI_MAG3] = ELFMAG3;
	elf_file.ehdr.e_ident[EI_VERSION] = EV_CURRENT;
	elf_file.ehdr.e_ident[EI_CLASS] = ELFCLASS64;
#if BYTE_ORDER == _BIG_ENDIAN
	elf_file.ehdr.e_ident[EI_DATA] = ELFDATA2MSB;
#else
	elf_file.ehdr.e_ident[EI_DATA] = ELFDATA2LSB;
#endif
#if defined(__FreeBSD__)
	elf_file.ehdr.e_ident[EI_OSABI] = ELFOSABI_FREEBSD;
#endif
	elf_file.ehdr.e_type = ET_REL;
#if defined(__arm__)
	elf_file.ehdr.e_machine = EM_ARM;
#elif defined(__mips__)
	elf_file.ehdr.e_machine = EM_MIPS;
#elif defined(__powerpc64__)
	elf_file.ehdr.e_machine = EM_PPC64;
#elif defined(__sparc)
	elf_file.ehdr.e_machine = EM_SPARCV9;
#elif defined(__i386) || defined(__amd64)
	elf_file.ehdr.e_machine = EM_AMD64;
#elif defined(__aarch64__)
	elf_file.ehdr.e_machine = EM_AARCH64;
#endif
	elf_file.ehdr.e_version = EV_CURRENT;
	elf_file.ehdr.e_shoff = sizeof (Elf64_Ehdr);
	elf_file.ehdr.e_ehsize = sizeof (Elf64_Ehdr);
	elf_file.ehdr.e_phentsize = sizeof (Elf64_Phdr);
	elf_file.ehdr.e_shentsize = sizeof (Elf64_Shdr);
	elf_file.ehdr.e_shnum = nshdr;
	elf_file.ehdr.e_shstrndx = ESHDR_SHSTRTAB;
	off = sizeof (elf_file) + nshdr * sizeof (Elf64_Shdr);

	shp = &elf_file.shdr[ESHDR_SHSTRTAB];
	shp->sh_name = 1; /* DTRACE_SHSTRTAB64[1] = ".shstrtab" */
	shp->sh_type = SHT_STRTAB;
	shp->sh_offset = off;
	shp->sh_size = sizeof (DTRACE_SHSTRTAB64);
	shp->sh_addralign = sizeof (char);
	off = P2ROUNDUP(shp->sh_offset + shp->sh_size, 8);

	shp = &elf_file.shdr[ESHDR_DOF];
	shp->sh_name = 11; /* DTRACE_SHSTRTAB64[11] = ".SUNW_dof" */
	shp->sh_flags = SHF_ALLOC;
	shp->sh_type = SHT_SUNW_dof;
	shp->sh_offset = off;
	shp->sh_size = dof->dofh_filesz;
	shp->sh_addralign = 8;
	off = shp->sh_offset + shp->sh_size;

	shp = &elf_file.shdr[ESHDR_STRTAB];
	shp->sh_name = 21; /* DTRACE_SHSTRTAB64[21] = ".strtab" */
	shp->sh_flags = SHF_ALLOC;
	shp->sh_type = SHT_STRTAB;
	shp->sh_offset = off;
	shp->sh_size = de.de_strlen;
	shp->sh_addralign = sizeof (char);
	off = P2ROUNDUP(shp->sh_offset + shp->sh_size, 8);

	shp = &elf_file.shdr[ESHDR_SYMTAB];
	shp->sh_name = 29; /* DTRACE_SHSTRTAB64[29] = ".symtab" */
	shp->sh_flags = SHF_ALLOC;
	shp->sh_type = SHT_SYMTAB;
	shp->sh_entsize = sizeof (Elf64_Sym);
	shp->sh_link = ESHDR_STRTAB;
	shp->sh_offset = off;
	shp->sh_info = de.de_global;
	shp->sh_size = de.de_nsym * sizeof (Elf64_Sym);
	shp->sh_addralign = 8;
	off = P2ROUNDUP(shp->sh_offset + shp->sh_size, 8);

	if (de.de_nrel == 0) {
		if (dt_write(dtp, fd, &elf_file,
		    sizeof (elf_file)) != sizeof (elf_file) ||
		    PWRITE_SCN(ESHDR_SHSTRTAB, DTRACE_SHSTRTAB64) ||
		    PWRITE_SCN(ESHDR_STRTAB, de.de_strtab) ||
		    PWRITE_SCN(ESHDR_SYMTAB, de.de_sym) ||
		    PWRITE_SCN(ESHDR_DOF, dof)) {
			ret = dt_set_errno(dtp, errno);
		}
	} else {
		shp = &elf_file.shdr[ESHDR_REL];
		shp->sh_name = 37; /* DTRACE_SHSTRTAB64[37] = ".rel.SUNW_dof" */
		shp->sh_flags = SHF_ALLOC;
		shp->sh_type = SHT_RELA;
		shp->sh_entsize = sizeof (de.de_rel[0]);
		shp->sh_link = ESHDR_SYMTAB;
		shp->sh_info = ESHDR_DOF;
		shp->sh_offset = off;
		shp->sh_size = de.de_nrel * sizeof (de.de_rel[0]);
		shp->sh_addralign = 8;

		if (dt_write(dtp, fd, &elf_file,
		    sizeof (elf_file)) != sizeof (elf_file) ||
		    PWRITE_SCN(ESHDR_SHSTRTAB, DTRACE_SHSTRTAB64) ||
		    PWRITE_SCN(ESHDR_STRTAB, de.de_strtab) ||
		    PWRITE_SCN(ESHDR_SYMTAB, de.de_sym) ||
		    PWRITE_SCN(ESHDR_REL, de.de_rel) ||
		    PWRITE_SCN(ESHDR_DOF, dof)) {
			ret = dt_set_errno(dtp, errno);
		}
	}

	free(de.de_strtab);
	free(de.de_sym);
	free(de.de_rel);

	return (ret);
}

static int
dt_symtab_lookup(Elf_Data *data_sym, int start, int end, uintptr_t addr,
    uint_t shn, GElf_Sym *sym, int uses_funcdesc, Elf *elf)
{
	Elf64_Addr symval;
	Elf_Scn *opd_scn;
	Elf_Data *opd_desc;
	int i;

	for (i = start; i < end && gelf_getsym(data_sym, i, sym) != NULL; i++) {
		if (GELF_ST_TYPE(sym->st_info) == STT_FUNC) {
			symval = sym->st_value;
			if (uses_funcdesc) {
				opd_scn = elf_getscn(elf, sym->st_shndx);
				opd_desc = elf_rawdata(opd_scn, NULL);
				symval =
				    *(uint64_t*)((char *)opd_desc->d_buf + symval);
			}
			if ((uses_funcdesc || shn == sym->st_shndx) &&
			    symval <= addr && addr < symval + sym->st_size)
				return (0);
		}
	}

	return (-1);
}

#if defined(__aarch64__)
#define	DT_OP_NOP		0xd503201f
#define	DT_OP_RET		0xd65f03c0
#define	DT_OP_CALL26		0x94000000
#define	DT_OP_JUMP26		0x14000000

static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	uint32_t *ip;

	/*
	 * Ensure that the offset is aligned on an instruction boundary.
	 */
	if ((rela->r_offset & (sizeof (uint32_t) - 1)) != 0)
		return (-1);

	/*
	 * We only know about some specific relocation types.
	 * We also recognize relocation type NONE, since that gets used for
	 * relocations of USDT probes, and we might be re-processing a file.
	 */
	if (GELF_R_TYPE(rela->r_info) != R_AARCH64_CALL26 &&
	    GELF_R_TYPE(rela->r_info) != R_AARCH64_JUMP26 &&
	    GELF_R_TYPE(rela->r_info) != R_AARCH64_NONE)
		return (-1);

	ip = (uint32_t *)(p + rela->r_offset);

	/*
	 * We may have already processed this object file in an earlier linker
	 * invocation. Check to see if the present instruction sequence matches
	 * the one we would install below.
	 */
	if (ip[0] == DT_OP_NOP || ip[0] == DT_OP_RET)
		return (0);

	/*
	 * We only expect call instructions with a displacement of 0, or a jump
	 * instruction acting as a tail call.
	 */
	if (ip[0] != DT_OP_CALL26 && ip[0] != DT_OP_JUMP26) {
		dt_dprintf("found %x instead of a call or jmp instruction at "
		    "%llx\n", ip[0], (u_longlong_t)rela->r_offset);
		return (-1);
	}

	/*
	 * On arm64, we do not have to differentiate between regular probes and
	 * is-enabled probes.  Both cases are encoded as a regular branch for
	 * non-tail call locations, and a jump for tail call locations.  Calls
	 * are to be converted into a no-op whereas jumps should become a
	 * return.
	 */
	if (ip[0] == DT_OP_CALL26)
		ip[0] = DT_OP_NOP;
	else
		ip[0] = DT_OP_RET;

	return (0);
}
#elif defined(__arm__)
/* XXX */
static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	printf("%s:%s(%d): arm not implemented\n", __FUNCTION__, __FILE__,
	    __LINE__);
	return (-1);
}
#elif defined(__mips__)
/* XXX */
static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	printf("%s:%s(%d): MIPS not implemented\n", __FUNCTION__, __FILE__,
	    __LINE__);
	return (-1);
}
#elif defined(__powerpc__)
/* The sentinel is 'xor r3,r3,r3'. */
#define DT_OP_XOR_R3	0x7c631a78

#define DT_OP_NOP		0x60000000
#define DT_OP_BLR		0x4e800020

/* This captures all forms of branching to address. */
#define DT_IS_BRANCH(inst)	((inst & 0xfc000000) == 0x48000000)
#define DT_IS_BL(inst)	(DT_IS_BRANCH(inst) && (inst & 0x01))

/* XXX */
static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	uint32_t *ip;

	if ((rela->r_offset & (sizeof (uint32_t) - 1)) != 0)
		return (-1);

	/*LINTED*/
	ip = (uint32_t *)(p + rela->r_offset);

	/*
	 * We only know about some specific relocation types.
	 */
	if (GELF_R_TYPE(rela->r_info) != R_PPC_REL24 &&
	    GELF_R_TYPE(rela->r_info) != R_PPC_PLTREL24)
		return (-1);

	/*
	 * We may have already processed this object file in an earlier linker
	 * invocation. Check to see if the present instruction sequence matches
	 * the one we would install below.
	 */
	if (isenabled) {
		if (ip[0] == DT_OP_XOR_R3) {
			(*off) += sizeof (ip[0]);
			return (0);
		}
	} else {
		if (ip[0] == DT_OP_NOP) {
			(*off) += sizeof (ip[0]);
			return (0);
		}
	}

	/*
	 * We only expect branch to address instructions.
	 */
	if (!DT_IS_BRANCH(ip[0])) {
		dt_dprintf("found %x instead of a branch instruction at %llx\n",
		    ip[0], (u_longlong_t)rela->r_offset);
		return (-1);
	}

	if (isenabled) {
		/*
		 * It would necessarily indicate incorrect usage if an is-
		 * enabled probe were tail-called so flag that as an error.
		 * It's also potentially (very) tricky to handle gracefully,
		 * but could be done if this were a desired use scenario.
		 */
		if (!DT_IS_BL(ip[0])) {
			dt_dprintf("tail call to is-enabled probe at %llx\n",
			    (u_longlong_t)rela->r_offset);
			return (-1);
		}

		ip[0] = DT_OP_XOR_R3;
		(*off) += sizeof (ip[0]);
	} else {
		if (DT_IS_BL(ip[0]))
			ip[0] = DT_OP_NOP;
		else
			ip[0] = DT_OP_BLR;
	}

	return (0);
}
#elif defined(__riscv)
/* XXX */
static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	printf("%s:%s(%d): RISC-V implementation required\n", __FUNCTION__,
	    __FILE__, __LINE__);
	return (-1);
}
#elif defined(__sparc)

#define	DT_OP_RET		0x81c7e008
#define	DT_OP_NOP		0x01000000
#define	DT_OP_CALL		0x40000000
#define	DT_OP_CLR_O0		0x90102000

#define	DT_IS_MOV_O7(inst)	(((inst) & 0xffffe000) == 0x9e100000)
#define	DT_IS_RESTORE(inst)	(((inst) & 0xc1f80000) == 0x81e80000)
#define	DT_IS_RETL(inst)	(((inst) & 0xfff83fff) == 0x81c02008)

#define	DT_RS2(inst)		((inst) & 0x1f)
#define	DT_MAKE_RETL(reg)	(0x81c02008 | ((reg) << 14))

/*ARGSUSED*/
static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	uint32_t *ip;

	if ((rela->r_offset & (sizeof (uint32_t) - 1)) != 0)
		return (-1);

	/*LINTED*/
	ip = (uint32_t *)(p + rela->r_offset);

	/*
	 * We only know about some specific relocation types.
	 */
	if (GELF_R_TYPE(rela->r_info) != R_SPARC_WDISP30 &&
	    GELF_R_TYPE(rela->r_info) != R_SPARC_WPLT30)
		return (-1);

	/*
	 * We may have already processed this object file in an earlier linker
	 * invocation. Check to see if the present instruction sequence matches
	 * the one we would install below.
	 */
	if (isenabled) {
		if (ip[0] == DT_OP_NOP) {
			(*off) += sizeof (ip[0]);
			return (0);
		}
	} else {
		if (DT_IS_RESTORE(ip[1])) {
			if (ip[0] == DT_OP_RET) {
				(*off) += sizeof (ip[0]);
				return (0);
			}
		} else if (DT_IS_MOV_O7(ip[1])) {
			if (DT_IS_RETL(ip[0]))
				return (0);
		} else {
			if (ip[0] == DT_OP_NOP) {
				(*off) += sizeof (ip[0]);
				return (0);
			}
		}
	}

	/*
	 * We only expect call instructions with a displacement of 0.
	 */
	if (ip[0] != DT_OP_CALL) {
		dt_dprintf("found %x instead of a call instruction at %llx\n",
		    ip[0], (u_longlong_t)rela->r_offset);
		return (-1);
	}

	if (isenabled) {
		/*
		 * It would necessarily indicate incorrect usage if an is-
		 * enabled probe were tail-called so flag that as an error.
		 * It's also potentially (very) tricky to handle gracefully,
		 * but could be done if this were a desired use scenario.
		 */
		if (DT_IS_RESTORE(ip[1]) || DT_IS_MOV_O7(ip[1])) {
			dt_dprintf("tail call to is-enabled probe at %llx\n",
			    (u_longlong_t)rela->r_offset);
			return (-1);
		}


		/*
		 * On SPARC, we take advantage of the fact that the first
		 * argument shares the same register as for the return value.
		 * The macro handles the work of zeroing that register so we
		 * don't need to do anything special here. We instrument the
		 * instruction in the delay slot as we'll need to modify the
		 * return register after that instruction has been emulated.
		 */
		ip[0] = DT_OP_NOP;
		(*off) += sizeof (ip[0]);
	} else {
		/*
		 * If the call is followed by a restore, it's a tail call so
		 * change the call to a ret. If the call if followed by a mov
		 * of a register into %o7, it's a tail call in leaf context
		 * so change the call to a retl-like instruction that returns
		 * to that register value + 8 (rather than the typical %o7 +
		 * 8); the delay slot instruction is left, but should have no
		 * effect. Otherwise we change the call to be a nop. We
		 * identify the subsequent instruction as the probe point in
		 * all but the leaf tail-call case to ensure that arguments to
		 * the probe are complete and consistent. An astute, though
		 * largely hypothetical, observer would note that there is the
		 * possibility of a false-positive probe firing if the function
		 * contained a branch to the instruction in the delay slot of
		 * the call. Fixing this would require significant in-kernel
		 * modifications, and isn't worth doing until we see it in the
		 * wild.
		 */
		if (DT_IS_RESTORE(ip[1])) {
			ip[0] = DT_OP_RET;
			(*off) += sizeof (ip[0]);
		} else if (DT_IS_MOV_O7(ip[1])) {
			ip[0] = DT_MAKE_RETL(DT_RS2(ip[1]));
		} else {
			ip[0] = DT_OP_NOP;
			(*off) += sizeof (ip[0]);
		}
	}

	return (0);
}

#elif defined(__i386) || defined(__amd64)

#define	DT_OP_NOP		0x90
#define	DT_OP_RET		0xc3
#define	DT_OP_CALL		0xe8
#define	DT_OP_JMP32		0xe9
#define	DT_OP_REX_RAX		0x48
#define	DT_OP_XOR_EAX_0		0x33
#define	DT_OP_XOR_EAX_1		0xc0

static int
dt_modtext(dtrace_hdl_t *dtp, char *p, int isenabled, GElf_Rela *rela,
    uint32_t *off)
{
	uint8_t *ip = (uint8_t *)(p + rela->r_offset - 1);
	uint8_t ret;

	/*
	 * On x86, the first byte of the instruction is the call opcode and
	 * the next four bytes are the 32-bit address; the relocation is for
	 * the address operand. We back up the offset to the first byte of
	 * the instruction. For is-enabled probes, we later advance the offset
	 * so that it hits the first nop in the instruction sequence.
	 */
	(*off) -= 1;

	/*
	 * We only know about some specific relocation types. Luckily
	 * these types have the same values on both 32-bit and 64-bit
	 * x86 architectures.
	 */
	if (GELF_R_TYPE(rela->r_info) != R_386_PC32 &&
	    GELF_R_TYPE(rela->r_info) != R_386_PLT32)
		return (-1);

	/*
	 * We may have already processed this object file in an earlier linker
	 * invocation. Check to see if the present instruction sequence matches
	 * the one we would install. For is-enabled probes, we advance the
	 * offset to the first nop instruction in the sequence to match the
	 * text modification code below.
	 */
	if (!isenabled) {
		if ((ip[0] == DT_OP_NOP || ip[0] == DT_OP_RET) &&
		    ip[1] == DT_OP_NOP && ip[2] == DT_OP_NOP &&
		    ip[3] == DT_OP_NOP && ip[4] == DT_OP_NOP)
			return (0);
	} else if (dtp->dt_oflags & DTRACE_O_LP64) {
		if (ip[0] == DT_OP_REX_RAX &&
		    ip[1] == DT_OP_XOR_EAX_0 && ip[2] == DT_OP_XOR_EAX_1 &&
		    (ip[3] == DT_OP_NOP || ip[3] == DT_OP_RET) &&
		    ip[4] == DT_OP_NOP) {
			(*off) += 3;
			return (0);
		}
	} else {
		if (ip[0] == DT_OP_XOR_EAX_0 && ip[1] == DT_OP_XOR_EAX_1 &&
		    (ip[2] == DT_OP_NOP || ip[2] == DT_OP_RET) &&
		    ip[3] == DT_OP_NOP && ip[4] == DT_OP_NOP) {
			(*off) += 2;
			return (0);
		}
	}

	/*
	 * We expect either a call instrution with a 32-bit displacement or a
	 * jmp instruction with a 32-bit displacement acting as a tail-call.
	 */
	if (ip[0] != DT_OP_CALL && ip[0] != DT_OP_JMP32) {
		dt_dprintf("found %x instead of a call or jmp instruction at "
		    "%llx\n", ip[0], (u_longlong_t)rela->r_offset);
		return (-1);
	}

	ret = (ip[0] == DT_OP_JMP32) ? DT_OP_RET : DT_OP_NOP;

	/*
	 * Establish the instruction sequence -- all nops for probes, and an
	 * instruction to clear the return value register (%eax/%rax) followed
	 * by nops for is-enabled probes. For is-enabled probes, we advance
	 * the offset to the first nop. This isn't stricly necessary but makes
	 * for more readable disassembly when the probe is enabled.
	 */
	if (!isenabled) {
		ip[0] = ret;
		ip[1] = DT_OP_NOP;
		ip[2] = DT_OP_NOP;
		ip[3] = DT_OP_NOP;
		ip[4] = DT_OP_NOP;
	} else if (dtp->dt_oflags & DTRACE_O_LP64) {
		ip[0] = DT_OP_REX_RAX;
		ip[1] = DT_OP_XOR_EAX_0;
		ip[2] = DT_OP_XOR_EAX_1;
		ip[3] = ret;
		ip[4] = DT_OP_NOP;
		(*off) += 3;
	} else {
		ip[0] = DT_OP_XOR_EAX_0;
		ip[1] = DT_OP_XOR_EAX_1;
		ip[2] = ret;
		ip[3] = DT_OP_NOP;
		ip[4] = DT_OP_NOP;
		(*off) += 2;
	}

	return (0);
}

#else
#error unknown ISA
#endif

/*PRINTFLIKE5*/
static int
dt_link_error(dtrace_hdl_t *dtp, Elf *elf, int fd, dt_link_pair_t *bufs,
    const char *format, ...)
{
	va_list ap;
	dt_link_pair_t *pair;

	va_start(ap, format);
	dt_set_errmsg(dtp, NULL, NULL, NULL, 0, format, ap);
	va_end(ap);

	if (elf != NULL)
		(void) elf_end(elf);

	if (fd >= 0)
		(void) close(fd);

	while ((pair = bufs) != NULL) {
		bufs = pair->dlp_next;
		dt_free(dtp, pair->dlp_str);
		dt_free(dtp, pair->dlp_sym);
		dt_free(dtp, pair);
	}

	return (dt_set_errno(dtp, EDT_COMPILER));
}

static int
process_obj(dtrace_hdl_t *dtp, const char *obj, int *eprobesp)
{
	static const char dt_prefix[] = "__dtrace";
	static const char dt_enabled[] = "enabled";
	static const char dt_symprefix[] = "$dtrace";
	static const char dt_symfmt[] = "%s%ld.%s";
	static const char dt_weaksymfmt[] = "%s.%s";
	char probename[DTRACE_NAMELEN];
	int fd, i, ndx, eprobe, mod = 0;
	Elf *elf = NULL;
	GElf_Ehdr ehdr;
	Elf_Scn *scn_rel, *scn_sym, *scn_str, *scn_tgt;
	Elf_Data *data_rel, *data_sym, *data_str, *data_tgt;
	GElf_Shdr shdr_rel, shdr_sym, shdr_str, shdr_tgt;
	GElf_Sym rsym, fsym, dsym;
	GElf_Rela rela;
	char *s, *p, *r;
	char pname[DTRACE_PROVNAMELEN];
	dt_provider_t *pvp;
	dt_probe_t *prp;
	uint32_t off, eclass, emachine1, emachine2;
	size_t symsize, osym, nsym, isym, istr, len;
	key_t objkey;
	dt_link_pair_t *pair, *bufs = NULL;
	dt_strtab_t *strtab;
	void *tmp;

	if ((fd = open64(obj, O_RDWR)) == -1) {
		return (dt_link_error(dtp, elf, fd, bufs,
		    "failed to open %s: %s", obj, strerror(errno)));
	}

	if ((elf = elf_begin(fd, ELF_C_RDWR, NULL)) == NULL) {
		return (dt_link_error(dtp, elf, fd, bufs,
		    "failed to process %s: %s", obj, elf_errmsg(elf_errno())));
	}

	switch (elf_kind(elf)) {
	case ELF_K_ELF:
		break;
	case ELF_K_AR:
		return (dt_link_error(dtp, elf, fd, bufs, "archives are not "
		    "permitted; use the contents of the archive instead: %s",
		    obj));
	default:
		return (dt_link_error(dtp, elf, fd, bufs,
		    "invalid file type: %s", obj));
	}

	if (gelf_getehdr(elf, &ehdr) == NULL) {
		return (dt_link_error(dtp, elf, fd, bufs, "corrupt file: %s",
		    obj));
	}

	if (dtp->dt_oflags & DTRACE_O_LP64) {
		eclass = ELFCLASS64;
#if defined(__mips__)
		emachine1 = emachine2 = EM_MIPS;
#elif defined(__powerpc__)
		emachine1 = emachine2 = EM_PPC64;
#elif defined(__sparc)
		emachine1 = emachine2 = EM_SPARCV9;
#elif defined(__i386) || defined(__amd64)
		emachine1 = emachine2 = EM_AMD64;
#elif defined(__aarch64__)
		emachine1 = emachine2 = EM_AARCH64;
#endif
		symsize = sizeof (Elf64_Sym);
	} else {
		eclass = ELFCLASS32;
#if defined(__arm__)
		emachine1 = emachine2 = EM_ARM;
#elif defined(__mips__)
		emachine1 = emachine2 = EM_MIPS;
#elif defined(__powerpc__)
		emachine1 = emachine2 = EM_PPC;
#elif defined(__sparc)
		emachine1 = EM_SPARC;
		emachine2 = EM_SPARC32PLUS;
#elif defined(__i386) || defined(__amd64)
		emachine1 = emachine2 = EM_386;
#endif
		symsize = sizeof (Elf32_Sym);
	}

	if (ehdr.e_ident[EI_CLASS] != eclass) {
		return (dt_link_error(dtp, elf, fd, bufs,
		    "incorrect ELF class for object file: %s", obj));
	}

	if (ehdr.e_machine != emachine1 && ehdr.e_machine != emachine2) {
		return (dt_link_error(dtp, elf, fd, bufs,
		    "incorrect ELF machine type for object file: %s", obj));
	}

	/*
	 * We use this token as a relatively unique handle for this file on the
	 * system in order to disambiguate potential conflicts between files of
	 * the same name which contain identially named local symbols.
	 */
	if ((objkey = ftok(obj, 0)) == (key_t)-1) {
		return (dt_link_error(dtp, elf, fd, bufs,
		    "failed to generate unique key for object file: %s", obj));
	}

	scn_rel = NULL;
	while ((scn_rel = elf_nextscn(elf, scn_rel)) != NULL) {
		if (gelf_getshdr(scn_rel, &shdr_rel) == NULL)
			goto err;

		/*
		 * Skip any non-relocation sections.
		 */
		if (shdr_rel.sh_type != SHT_RELA && shdr_rel.sh_type != SHT_REL)
			continue;

		if ((data_rel = elf_getdata(scn_rel, NULL)) == NULL)
			goto err;

		/*
		 * Grab the section, section header and section data for the
		 * symbol table that this relocation section references.
		 */
		if ((scn_sym = elf_getscn(elf, shdr_rel.sh_link)) == NULL ||
		    gelf_getshdr(scn_sym, &shdr_sym) == NULL ||
		    (data_sym = elf_getdata(scn_sym, NULL)) == NULL)
			goto err;

		/*
		 * Ditto for that symbol table's string table.
		 */
		if ((scn_str = elf_getscn(elf, shdr_sym.sh_link)) == NULL ||
		    gelf_getshdr(scn_str, &shdr_str) == NULL ||
		    (data_str = elf_getdata(scn_str, NULL)) == NULL)
			goto err;

		/*
		 * Grab the section, section header and section data for the
		 * target section for the relocations. For the relocations
		 * we're looking for -- this will typically be the text of the
		 * object file.
		 */
		if ((scn_tgt = elf_getscn(elf, shdr_rel.sh_info)) == NULL ||
		    gelf_getshdr(scn_tgt, &shdr_tgt) == NULL ||
		    (data_tgt = elf_getdata(scn_tgt, NULL)) == NULL)
			goto err;

		/*
		 * We're looking for relocations to symbols matching this form:
		 *
		 *   __dtrace[enabled]_<prov>___<probe>
		 *
		 * For the generated object, we need to record the location
		 * identified by the relocation, and create a new relocation
		 * in the generated object that will be resolved at link time
		 * to the location of the function in which the probe is
		 * embedded. In the target object, we change the matched symbol
		 * so that it will be ignored at link time, and we modify the
		 * target (text) section to replace the call instruction with
		 * one or more nops.
		 *
		 * To avoid runtime overhead, the relocations added to the
		 * generated object should be resolved at static link time. We
		 * therefore create aliases for the functions that contain
		 * probes. An alias is global (so that the relocation from the
		 * generated object can be resolved), and hidden (so that its
		 * address is known at static link time). Such aliases have this
		 * form:
		 *
		 *   $dtrace<key>.<function>
		 *
		 * We take a first pass through all the relocations to
		 * populate our string table and count the number of extra
		 * symbols we'll require.
		 */
		strtab = dt_strtab_create(1);
		nsym = 0;
		isym = data_sym->d_size / symsize;
		istr = data_str->d_size;

		for (i = 0; i < shdr_rel.sh_size / shdr_rel.sh_entsize; i++) {

			if (shdr_rel.sh_type == SHT_RELA) {
				if (gelf_getrela(data_rel, i, &rela) == NULL)
					continue;
			} else {
				GElf_Rel rel;
				if (gelf_getrel(data_rel, i, &rel) == NULL)
					continue;
				rela.r_offset = rel.r_offset;
				rela.r_info = rel.r_info;
				rela.r_addend = 0;
			}

			if (gelf_getsym(data_sym, GELF_R_SYM(rela.r_info),
			    &rsym) == NULL) {
				dt_strtab_destroy(strtab);
				goto err;
			}

			s = (char *)data_str->d_buf + rsym.st_name;

			if (strncmp(s, dt_prefix, sizeof (dt_prefix) - 1) != 0)
				continue;

			if (dt_symtab_lookup(data_sym, 0, isym, rela.r_offset,
			    shdr_rel.sh_info, &fsym, (emachine1 == EM_PPC64),
			    elf) != 0) {
				dt_strtab_destroy(strtab);
				goto err;
			}

			if (fsym.st_name > data_str->d_size) {
				dt_strtab_destroy(strtab);
				goto err;
			}

			s = (char *)data_str->d_buf + fsym.st_name;

			/*
			 * If this symbol isn't of type function, we've really
			 * driven off the rails or the object file is corrupt.
			 */
			if (GELF_ST_TYPE(fsym.st_info) != STT_FUNC) {
				dt_strtab_destroy(strtab);
				return (dt_link_error(dtp, elf, fd, bufs,
				    "expected %s to be of type function", s));
			}

			/*
			 * Aliases of weak symbols don't get a uniquifier.
			 */
			if (GELF_ST_BIND(fsym.st_info) == STB_WEAK)
				len = snprintf(NULL, 0, dt_weaksymfmt,
				    dt_symprefix, s) + 1;
			else
				len = snprintf(NULL, 0, dt_symfmt, dt_symprefix,
				    objkey, s) + 1;
			if ((p = dt_alloc(dtp, len)) == NULL) {
				dt_strtab_destroy(strtab);
				goto err;
			}
			(void) snprintf(p, len, dt_symfmt, dt_symprefix,
			    objkey, s);

			if (dt_strtab_index(strtab, p) == -1) {
				nsym++;
				(void) dt_strtab_insert(strtab, p);
			}

			dt_free(dtp, p);
		}

		/*
		 * If any probes were found, allocate the additional space for
		 * the symbol table and string table, copying the old data into
		 * the new buffers, and marking the buffers as dirty. We inject
		 * those newly allocated buffers into the libelf data
		 * structures, but are still responsible for freeing them once
		 * we're done with the elf handle.
		 */
		if (nsym > 0) {
			/*
			 * The first byte of the string table is reserved for
			 * the \0 entry.
			 */
			len = dt_strtab_size(strtab) - 1;

			assert(len > 0);
			assert(dt_strtab_index(strtab, "") == 0);

			dt_strtab_destroy(strtab);

			if ((pair = dt_alloc(dtp, sizeof (*pair))) == NULL)
				goto err;

			if ((pair->dlp_str = dt_alloc(dtp, data_str->d_size +
			    len)) == NULL) {
				dt_free(dtp, pair);
				goto err;
			}

			if ((pair->dlp_sym = dt_alloc(dtp, data_sym->d_size +
			    nsym * symsize)) == NULL) {
				dt_free(dtp, pair->dlp_str);
				dt_free(dtp, pair);
				goto err;
			}

			pair->dlp_next = bufs;
			bufs = pair;

			bcopy(data_str->d_buf, pair->dlp_str, data_str->d_size);
			tmp = data_str->d_buf;
			data_str->d_buf = pair->dlp_str;
			pair->dlp_str = tmp;
			data_str->d_size += len;
			(void) elf_flagdata(data_str, ELF_C_SET, ELF_F_DIRTY);

			shdr_str.sh_size += len;
			(void) gelf_update_shdr(scn_str, &shdr_str);

			bcopy(data_sym->d_buf, pair->dlp_sym, data_sym->d_size);
			tmp = data_sym->d_buf;
			data_sym->d_buf = pair->dlp_sym;
			pair->dlp_sym = tmp;
			data_sym->d_size += nsym * symsize;
			(void) elf_flagdata(data_sym, ELF_C_SET, ELF_F_DIRTY);

			shdr_sym.sh_size += nsym * symsize;
			(void) gelf_update_shdr(scn_sym, &shdr_sym);

			osym = isym;
			nsym += isym;
		} else {
			dt_strtab_destroy(strtab);
			continue;
		}

		/*
		 * Now that the tables have been allocated, perform the
		 * modifications described above.
		 */
		for (i = 0; i < shdr_rel.sh_size / shdr_rel.sh_entsize; i++) {

			if (shdr_rel.sh_type == SHT_RELA) {
				if (gelf_getrela(data_rel, i, &rela) == NULL)
					continue;
			} else {
				GElf_Rel rel;
				if (gelf_getrel(data_rel, i, &rel) == NULL)
					continue;
				rela.r_offset = rel.r_offset;
				rela.r_info = rel.r_info;
				rela.r_addend = 0;
			}

			ndx = GELF_R_SYM(rela.r_info);

			if (gelf_getsym(data_sym, ndx, &rsym) == NULL ||
			    rsym.st_name > data_str->d_size)
				goto err;

			s = (char *)data_str->d_buf + rsym.st_name;

			if (strncmp(s, dt_prefix, sizeof (dt_prefix) - 1) != 0)
				continue;

			s += sizeof (dt_prefix) - 1;

			/*
			 * Check to see if this is an 'is-enabled' check as
			 * opposed to a normal probe.
			 */
			if (strncmp(s, dt_enabled,
			    sizeof (dt_enabled) - 1) == 0) {
				s += sizeof (dt_enabled) - 1;
				eprobe = 1;
				*eprobesp = 1;
				dt_dprintf("is-enabled probe\n");
			} else {
				eprobe = 0;
				dt_dprintf("normal probe\n");
			}

			if (*s++ != '_')
				goto err;

			if ((p = strstr(s, "___")) == NULL ||
			    p - s >= sizeof (pname))
				goto err;

			bcopy(s, pname, p - s);
			pname[p - s] = '\0';

			if (dt_symtab_lookup(data_sym, osym, isym,
			    rela.r_offset, shdr_rel.sh_info, &fsym,
			    (emachine1 == EM_PPC64), elf) == 0) {
				if (fsym.st_name > data_str->d_size)
					goto err;

				r = s = (char *) data_str->d_buf + fsym.st_name;
				assert(strstr(s, dt_symprefix) == s);
				s = strchr(s, '.') + 1;
			} else if (dt_symtab_lookup(data_sym, 0, osym,
			    rela.r_offset, shdr_rel.sh_info, &fsym,
			    (emachine1 == EM_PPC64), elf) == 0) {
				u_int bind;

				bind = GELF_ST_BIND(fsym.st_info) == STB_WEAK ?
				    STB_WEAK : STB_GLOBAL;

				/*
				 * Emit an alias for the symbol. It needs to be
				 * non-preemptible so that .SUNW_dof relocations
				 * may be resolved at static link time. Aliases
				 * of weak symbols are given a non-unique name
				 * so that they may be merged by the linker.
				 */
				dsym = fsym;
				dsym.st_name = istr;
				dsym.st_info = GELF_ST_INFO(bind, STT_FUNC);
				dsym.st_other = GELF_ST_VISIBILITY(STV_HIDDEN);
				(void) gelf_update_sym(data_sym, isym, &dsym);
				r = (char *) data_str->d_buf + istr;
				s = (char *) data_str->d_buf + fsym.st_name;
				if (bind == STB_WEAK)
					istr += sprintf(r, dt_weaksymfmt,
					    dt_symprefix, s);
				else
					istr += sprintf(r, dt_symfmt,
					    dt_symprefix, objkey, s);
				istr++;
				isym++;
				assert(isym <= nsym);
			} else
				goto err;

			if ((pvp = dt_provider_lookup(dtp, pname)) == NULL) {
				return (dt_link_error(dtp, elf, fd, bufs,
				    "no such provider %s", pname));
			}

			if (strlcpy(probename, p + 3, sizeof (probename)) >=
			    sizeof (probename))
				return (dt_link_error(dtp, elf, fd, bufs,
				    "invalid probe name %s", probename));
			(void) strhyphenate(probename);
			if ((prp = dt_probe_lookup(pvp, probename)) == NULL)
				return (dt_link_error(dtp, elf, fd, bufs,
				    "no such probe %s", probename));

			assert(fsym.st_value <= rela.r_offset);

			off = rela.r_offset - fsym.st_value;
			if (dt_modtext(dtp, data_tgt->d_buf, eprobe,
			    &rela, &off) != 0)
				goto err;

			if (dt_probe_define(pvp, prp, s, r, off, eprobe) != 0) {
				return (dt_link_error(dtp, elf, fd, bufs,
				    "failed to allocate space for probe"));
			}
#ifndef illumos
			/*
			 * Our linker doesn't understand the SUNW_IGNORE ndx and
			 * will try to use this relocation when we build the
			 * final executable. Since we are done processing this
			 * relocation, mark it as inexistant and let libelf
			 * remove it from the file.
			 * If this wasn't done, we would have garbage added to
			 * the executable file as the symbol is going to be
			 * change from UND to ABS.
			 */
			if (shdr_rel.sh_type == SHT_RELA) {
				rela.r_offset = 0;
				rela.r_info  = 0;
				rela.r_addend = 0;
				(void) gelf_update_rela(data_rel, i, &rela);
			} else {
				GElf_Rel rel;
				rel.r_offset = 0;
				rel.r_info = 0;
				(void) gelf_update_rel(data_rel, i, &rel);
			}
#endif

			mod = 1;
			(void) elf_flagdata(data_tgt, ELF_C_SET, ELF_F_DIRTY);

			/*
			 * This symbol may already have been marked to
			 * be ignored by another relocation referencing
			 * the same symbol or if this object file has
			 * already been processed by an earlier link
			 * invocation.
			 */
#ifndef illumos
#define SHN_SUNW_IGNORE	SHN_ABS
#endif
			if (rsym.st_shndx != SHN_SUNW_IGNORE) {
				rsym.st_shndx = SHN_SUNW_IGNORE;
				(void) gelf_update_sym(data_sym, ndx, &rsym);
			}
		}
	}

	if (mod && elf_update(elf, ELF_C_WRITE) == -1)
		goto err;

	(void) elf_end(elf);
	(void) close(fd);

	while ((pair = bufs) != NULL) {
		bufs = pair->dlp_next;
		dt_free(dtp, pair->dlp_str);
		dt_free(dtp, pair->dlp_sym);
		dt_free(dtp, pair);
	}

	return (0);

err:
	return (dt_link_error(dtp, elf, fd, bufs,
	    "an error was encountered while processing %s", obj));
}

int
dtrace_program_link(dtrace_hdl_t *dtp, dtrace_prog_t *pgp, uint_t dflags,
    const char *file, int objc, char *const objv[])
{
#ifndef illumos
	char tfile[PATH_MAX];
#endif
	char drti[PATH_MAX];
	dof_hdr_t *dof;
	int fd, status, i, cur;
	char *cmd, tmp;
	size_t len;
	int eprobes = 0, ret = 0;

#ifndef illumos
	if (access(file, R_OK) == 0) {
		fprintf(stderr, "dtrace: target object (%s) already exists. "
		    "Please remove the target\ndtrace: object and rebuild all "
		    "the source objects if you wish to run the DTrace\n"
		    "dtrace: linking process again\n", file);
		/*
		 * Several build infrastructures run DTrace twice (e.g.
		 * postgres) and we don't want the build to fail. Return
		 * 0 here since this isn't really a fatal error.
		 */
		return (0);
	}
#endif

	/*
	 * A NULL program indicates a special use in which we just link
	 * together a bunch of object files specified in objv and then
	 * unlink(2) those object files.
	 */
	if (pgp == NULL) {
		const char *fmt = "%s -o %s -r";

		len = snprintf(&tmp, 1, fmt, dtp->dt_ld_path, file) + 1;

		for (i = 0; i < objc; i++)
			len += strlen(objv[i]) + 1;

		cmd = alloca(len);

		cur = snprintf(cmd, len, fmt, dtp->dt_ld_path, file);

		for (i = 0; i < objc; i++)
			cur += snprintf(cmd + cur, len - cur, " %s", objv[i]);

		if ((status = system(cmd)) == -1) {
			return (dt_link_error(dtp, NULL, -1, NULL,
			    "failed to run %s: %s", dtp->dt_ld_path,
			    strerror(errno)));
		}

		if (WIFSIGNALED(status)) {
			return (dt_link_error(dtp, NULL, -1, NULL,
			    "failed to link %s: %s failed due to signal %d",
			    file, dtp->dt_ld_path, WTERMSIG(status)));
		}

		if (WEXITSTATUS(status) != 0) {
			return (dt_link_error(dtp, NULL, -1, NULL,
			    "failed to link %s: %s exited with status %d\n",
			    file, dtp->dt_ld_path, WEXITSTATUS(status)));
		}

		for (i = 0; i < objc; i++) {
			if (strcmp(objv[i], file) != 0)
				(void) unlink(objv[i]);
		}

		return (0);
	}

	for (i = 0; i < objc; i++) {
		if (process_obj(dtp, objv[i], &eprobes) != 0)
			return (-1); /* errno is set for us */
	}

	/*
	 * If there are is-enabled probes then we need to force use of DOF
	 * version 2.
	 */
	if (eprobes && pgp->dp_dofversion < DOF_VERSION_2)
		pgp->dp_dofversion = DOF_VERSION_2;

	if ((dof = dtrace_dof_create(dtp, pgp, dflags)) == NULL)
		return (-1); /* errno is set for us */

#ifdef illumos
	/*
	 * Create a temporary file and then unlink it if we're going to
	 * combine it with drti.o later.  We can still refer to it in child
	 * processes as /dev/fd/<fd>.
	 */
	if ((fd = open64(file, O_RDWR | O_CREAT | O_TRUNC, 0666)) == -1) {
		return (dt_link_error(dtp, NULL, -1, NULL,
		    "failed to open %s: %s", file, strerror(errno)));
	}
#else
	snprintf(tfile, sizeof(tfile), "%s.XXXXXX", file);
	if ((fd = mkostemp(tfile, O_CLOEXEC)) == -1)
		return (dt_link_error(dtp, NULL, -1, NULL,
		    "failed to create temporary file %s: %s",
		    tfile, strerror(errno)));
#endif

	/*
	 * If -xlinktype=DOF has been selected, just write out the DOF.
	 * Otherwise proceed to the default of generating and linking ELF.
	 */
	switch (dtp->dt_linktype) {
	case DT_LTYP_DOF:
		if (dt_write(dtp, fd, dof, dof->dofh_filesz) < dof->dofh_filesz)
			ret = errno;

		if (close(fd) != 0 && ret == 0)
			ret = errno;

		if (ret != 0) {
			return (dt_link_error(dtp, NULL, -1, NULL,
			    "failed to write %s: %s", file, strerror(ret)));
		}

		return (0);

	case DT_LTYP_ELF:
		break; /* fall through to the rest of dtrace_program_link() */

	default:
		return (dt_link_error(dtp, NULL, -1, NULL,
		    "invalid link type %u\n", dtp->dt_linktype));
	}


#ifdef illumos
	if (!dtp->dt_lazyload)
		(void) unlink(file);
#endif

	if (dtp->dt_oflags & DTRACE_O_LP64)
		status = dump_elf64(dtp, dof, fd);
	else
		status = dump_elf32(dtp, dof, fd);

#ifdef illumos
	if (status != 0 || lseek(fd, 0, SEEK_SET) != 0) {
		return (dt_link_error(dtp, NULL, -1, NULL,
		    "failed to write %s: %s", file, strerror(errno)));
	}
#else
	if (status != 0)
		return (dt_link_error(dtp, NULL, -1, NULL,
		    "failed to write %s: %s", tfile,
		    strerror(dtrace_errno(dtp))));
#endif

	if (!dtp->dt_lazyload) {
#ifdef illumos
		const char *fmt = "%s -o %s -r -Blocal -Breduce /dev/fd/%d %s";

		if (dtp->dt_oflags & DTRACE_O_LP64) {
			(void) snprintf(drti, sizeof (drti),
			    "%s/64/drti.o", _dtrace_libdir);
		} else {
			(void) snprintf(drti, sizeof (drti),
			    "%s/drti.o", _dtrace_libdir);
		}

		len = snprintf(&tmp, 1, fmt, dtp->dt_ld_path, file, fd,
		    drti) + 1;

		cmd = alloca(len);

		(void) snprintf(cmd, len, fmt, dtp->dt_ld_path, file, fd, drti);
#else
		const char *fmt = "%s -o %s -r %s %s";
		dt_dirpath_t *dp = dt_list_next(&dtp->dt_lib_path);

		(void) snprintf(drti, sizeof (drti), "%s/drti.o", dp->dir_path);

		len = snprintf(&tmp, 1, fmt, dtp->dt_ld_path, file, tfile,
		    drti) + 1;

		cmd = alloca(len);

		(void) snprintf(cmd, len, fmt, dtp->dt_ld_path, file, tfile,
		    drti);
#endif
		if ((status = system(cmd)) == -1) {
			ret = dt_link_error(dtp, NULL, fd, NULL,
			    "failed to run %s: %s", dtp->dt_ld_path,
			    strerror(errno));
			goto done;
		}

		if (WIFSIGNALED(status)) {
			ret = dt_link_error(dtp, NULL, fd, NULL,
			    "failed to link %s: %s failed due to signal %d",
			    file, dtp->dt_ld_path, WTERMSIG(status));
			goto done;
		}

		if (WEXITSTATUS(status) != 0) {
			ret = dt_link_error(dtp, NULL, fd, NULL,
			    "failed to link %s: %s exited with status %d\n",
			    file, dtp->dt_ld_path, WEXITSTATUS(status));
			goto done;
		}
		(void) close(fd); /* release temporary file */

#ifdef __FreeBSD__
		/*
		 * Now that we've linked drti.o, reduce the global __SUNW_dof
		 * symbol to a local symbol. This is needed to so that multiple
		 * generated object files (for different providers, for
		 * instance) can be linked together. This is accomplished using
		 * the -Blocal flag with Sun's linker, but GNU ld doesn't appear
		 * to have an equivalent option.
		 */
		asprintf(&cmd, "%s --localize-hidden %s", dtp->dt_objcopy_path,
		    file);
		if ((status = system(cmd)) == -1) {
			ret = dt_link_error(dtp, NULL, -1, NULL,
			    "failed to run %s: %s", dtp->dt_objcopy_path,
			    strerror(errno));
			free(cmd);
			goto done;
		}
		free(cmd);

		if (WIFSIGNALED(status)) {
			ret = dt_link_error(dtp, NULL, -1, NULL,
			    "failed to link %s: %s failed due to signal %d",
			    file, dtp->dt_objcopy_path, WTERMSIG(status));
			goto done;
		}

		if (WEXITSTATUS(status) != 0) {
			ret = dt_link_error(dtp, NULL, -1, NULL,
			    "failed to link %s: %s exited with status %d\n",
			    file, dtp->dt_objcopy_path, WEXITSTATUS(status));
			goto done;
		}
#endif
	} else {
#ifdef __FreeBSD__
		if (rename(tfile, file) != 0) {
			ret = dt_link_error(dtp, NULL, fd, NULL,
			    "failed to rename %s to %s: %s", tfile, file,
			    strerror(errno));
			goto done;
		}
#endif
		(void) close(fd);
	}

done:
	dtrace_dof_destroy(dtp, dof);

#ifdef __FreeBSD__
	if (!dtp->dt_lazyload)
		(void) unlink(tfile);
#endif
	return (ret);
}