tools/perf/util/genelf.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /*
  * genelf.c
  * Copyright (C) 2014, Google, Inc
  *
  * Contributed by:
  * 	Stephane Eranian <eranian@gmail.com>
  *
  * Released under the GPL v2. (and only v2, not any later version)
  */

 #include <sys/types.h>
 #include <stdio.h>
 #include <getopt.h>
 #include <stddef.h>
 #include <libelf.h>
 #include <string.h>
 #include <stdlib.h>
 #include <inttypes.h>
 #include <limits.h>
 #include <fcntl.h>
 #include <err.h>
 #ifdef HAVE_DWARF_SUPPORT
 #include <dwarf.h>
 #endif

 #include "perf.h"
 #include "genelf.h"
 #include "../util/jitdump.h"

 #ifndef NT_GNU_BUILD_ID
 #define NT_GNU_BUILD_ID 3
 #endif

 #define JVMTI

 #define BUILD_ID_URANDOM /* different uuid for each run */

 // FIXME, remove this and fix the deprecation warnings before its removed and
 // We'll break for good here...
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"

 #ifdef HAVE_LIBCRYPTO_SUPPORT

 #define BUILD_ID_MD5
 #undef BUILD_ID_SHA	/* does not seem to work well when linked with Java */
 #undef BUILD_ID_URANDOM /* different uuid for each run */

 #ifdef BUILD_ID_SHA
 #include <openssl/sha.h>
 #endif

 #ifdef BUILD_ID_MD5
 #include <openssl/md5.h>
 #endif
 #endif


 typedef struct {
   unsigned int namesz;  /* Size of entry's owner string */
   unsigned int descsz;  /* Size of the note descriptor */
   unsigned int type;    /* Interpretation of the descriptor */
   char         name[0]; /* Start of the name+desc data */
 } Elf_Note;

 struct options {
 	char *output;
 	int fd;
 };

 static char shd_string_table[] = {
 	0,
 	'.', 't', 'e', 'x', 't', 0,			/*  1 */
 	'.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /*  7 */
 	'.', 's', 'y', 'm', 't', 'a', 'b', 0,		/* 17 */
 	'.', 's', 't', 'r', 't', 'a', 'b', 0,		/* 25 */
 	'.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
 	'.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
 	'.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
 	'.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
 	'.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
 	'.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
 };

 static struct buildid_note {
 	Elf_Note desc;		/* descsz: size of build-id, must be multiple of 4 */
 	char	 name[4];	/* GNU\0 */
 	char	 build_id[20];
 } bnote;

 static Elf_Sym symtab[]={
 	/* symbol 0 MUST be the undefined symbol */
 	{ .st_name  = 0, /* index in sym_string table */
 	  .st_info  = ELF_ST_TYPE(STT_NOTYPE),
 	  .st_shndx = 0, /* for now */
 	  .st_value = 0x0,
 	  .st_other = ELF_ST_VIS(STV_DEFAULT),
 	  .st_size  = 0,
 	},
 	{ .st_name  = 1, /* index in sym_string table */
 	  .st_info  = ELF_ST_BIND(STB_LOCAL) | ELF_ST_TYPE(STT_FUNC),
 	  .st_shndx = 1,
 	  .st_value = 0, /* for now */
 	  .st_other = ELF_ST_VIS(STV_DEFAULT),
 	  .st_size  = 0, /* for now */
 	}
 };

 #ifdef BUILD_ID_URANDOM
 static void
 gen_build_id(struct buildid_note *note,
 	     unsigned long load_addr __maybe_unused,
 	     const void *code __maybe_unused,
 	     size_t csize __maybe_unused)
 {
 	int fd;
 	size_t sz = sizeof(note->build_id);
 	ssize_t sret;

 	fd = open("/dev/urandom", O_RDONLY);
 	if (fd == -1)
 		err(1, "cannot access /dev/urandom for builid");

 	sret = read(fd, note->build_id, sz);

 	close(fd);

 	if (sret != (ssize_t)sz)
 		memset(note->build_id, 0, sz);
 }
 #endif

 #ifdef BUILD_ID_SHA
 static void
 gen_build_id(struct buildid_note *note,
 	     unsigned long load_addr __maybe_unused,
 	     const void *code,
 	     size_t csize)
 {
 	if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
 		errx(1, "build_id too small for SHA1");

 	SHA1(code, csize, (unsigned char *)note->build_id);
 }
 #endif

 #ifdef BUILD_ID_MD5
 static void
 gen_build_id(struct buildid_note *note, unsigned long load_addr, const void *code, size_t csize)
 {
 	MD5_CTX context;

 	if (sizeof(note->build_id) < 16)
 		errx(1, "build_id too small for MD5");

 	MD5_Init(&context);
 	MD5_Update(&context, &load_addr, sizeof(load_addr));
 	MD5_Update(&context, code, csize);
 	MD5_Final((unsigned char *)note->build_id, &context);
 }
 #endif

 static int
 jit_add_eh_frame_info(Elf *e, void* unwinding, uint64_t unwinding_header_size,
 		      uint64_t unwinding_size, uint64_t base_offset)
 {
 	Elf_Data *d;
 	Elf_Scn *scn;
 	Elf_Shdr *shdr;
 	uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;

 	/*
 	 * setup eh_frame section
 	 */
 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		return -1;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		return -1;
 	}

 	d->d_align = 8;
 	d->d_off = 0LL;
 	d->d_buf = unwinding;
 	d->d_type = ELF_T_BYTE;
 	d->d_size = unwinding_table_size;
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		return -1;
 	}

 	shdr->sh_name = 104;
 	shdr->sh_type = SHT_PROGBITS;
 	shdr->sh_addr = base_offset;
 	shdr->sh_flags = SHF_ALLOC;
 	shdr->sh_entsize = 0;

 	/*
 	 * setup eh_frame_hdr section
 	 */
 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		return -1;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		return -1;
 	}

 	d->d_align = 4;
 	d->d_off = 0LL;
 	d->d_buf = unwinding + unwinding_table_size;
 	d->d_type = ELF_T_BYTE;
 	d->d_size = unwinding_header_size;
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		return -1;
 	}

 	shdr->sh_name = 90;
 	shdr->sh_type = SHT_PROGBITS;
 	shdr->sh_addr = base_offset + unwinding_table_size;
 	shdr->sh_flags = SHF_ALLOC;
 	shdr->sh_entsize = 0;

 	return 0;
 }

 /*
  * fd: file descriptor open for writing for the output file
  * load_addr: code load address (could be zero, just used for buildid)
  * sym: function name (for native code - used as the symbol)
  * code: the native code
  * csize: the code size in bytes
  */
 int
 jit_write_elf(int fd, uint64_t load_addr, const char *sym,
 	      const void *code, int csize,
 	      void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
 	      void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
 {
 	Elf *e;
 	Elf_Data *d;
 	Elf_Scn *scn;
 	Elf_Ehdr *ehdr;
 	Elf_Shdr *shdr;
 	uint64_t eh_frame_base_offset;
 	char *strsym = NULL;
 	int symlen;
 	int retval = -1;

 	if (elf_version(EV_CURRENT) == EV_NONE) {
 		warnx("ELF initialization failed");
 		return -1;
 	}

 	e = elf_begin(fd, ELF_C_WRITE, NULL);
 	if (!e) {
 		warnx("elf_begin failed");
 		goto error;
 	}

 	/*
 	 * setup ELF header
 	 */
 	ehdr = elf_newehdr(e);
 	if (!ehdr) {
 		warnx("cannot get ehdr");
 		goto error;
 	}

 	ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
 	ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
 	ehdr->e_machine = GEN_ELF_ARCH;
 	ehdr->e_type = ET_DYN;
 	ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
 	ehdr->e_version = EV_CURRENT;
 	ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */

 	/*
 	 * setup text section
 	 */
 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		goto error;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		goto error;
 	}

 	d->d_align = 16;
 	d->d_off = 0LL;
 	d->d_buf = (void *)code;
 	d->d_type = ELF_T_BYTE;
 	d->d_size = csize;
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		goto error;
 	}

 	shdr->sh_name = 1;
 	shdr->sh_type = SHT_PROGBITS;
 	shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
 	shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
 	shdr->sh_entsize = 0;

 	/*
 	 * Setup .eh_frame_hdr and .eh_frame
 	 */
 	if (unwinding) {
 		eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
 		retval = jit_add_eh_frame_info(e, unwinding,
 					       unwinding_header_size, unwinding_size,
 					       eh_frame_base_offset);
 		if (retval)
 			goto error;
 	}

 	/*
 	 * setup section headers string table
 	 */
 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		goto error;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		goto error;
 	}

 	d->d_align = 1;
 	d->d_off = 0LL;
 	d->d_buf = shd_string_table;
 	d->d_type = ELF_T_BYTE;
 	d->d_size = sizeof(shd_string_table);
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		goto error;
 	}

 	shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
 	shdr->sh_type = SHT_STRTAB;
 	shdr->sh_flags = 0;
 	shdr->sh_entsize = 0;

 	/*
 	 * setup symtab section
 	 */
 	symtab[1].st_size  = csize;
 	symtab[1].st_value = GEN_ELF_TEXT_OFFSET;

 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		goto error;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		goto error;
 	}

 	d->d_align = 8;
 	d->d_off = 0LL;
 	d->d_buf = symtab;
 	d->d_type = ELF_T_SYM;
 	d->d_size = sizeof(symtab);
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		goto error;
 	}

 	shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
 	shdr->sh_type = SHT_SYMTAB;
 	shdr->sh_flags = 0;
 	shdr->sh_entsize = sizeof(Elf_Sym);
 	shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */

 	/*
 	 * setup symbols string table
 	 * 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
 	 */
 	symlen = 2 + strlen(sym);
 	strsym = calloc(1, symlen);
 	if (!strsym) {
 		warnx("cannot allocate strsym");
 		goto error;
 	}
 	strcpy(strsym + 1, sym);

 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		goto error;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		goto error;
 	}

 	d->d_align = 1;
 	d->d_off = 0LL;
 	d->d_buf = strsym;
 	d->d_type = ELF_T_BYTE;
 	d->d_size = symlen;
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		goto error;
 	}

 	shdr->sh_name = 25; /* offset in shd_string_table */
 	shdr->sh_type = SHT_STRTAB;
 	shdr->sh_flags = 0;
 	shdr->sh_entsize = 0;

 	/*
 	 * setup build-id section
 	 */
 	scn = elf_newscn(e);
 	if (!scn) {
 		warnx("cannot create section");
 		goto error;
 	}

 	d = elf_newdata(scn);
 	if (!d) {
 		warnx("cannot get new data");
 		goto error;
 	}

 	/*
 	 * build-id generation
 	 */
 	gen_build_id(&bnote, load_addr, code, csize);
 	bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
 	bnote.desc.descsz = sizeof(bnote.build_id);
 	bnote.desc.type   = NT_GNU_BUILD_ID;
 	strcpy(bnote.name, "GNU");

 	d->d_align = 4;
 	d->d_off = 0LL;
 	d->d_buf = &bnote;
 	d->d_type = ELF_T_BYTE;
 	d->d_size = sizeof(bnote);
 	d->d_version = EV_CURRENT;

 	shdr = elf_getshdr(scn);
 	if (!shdr) {
 		warnx("cannot get section header");
 		goto error;
 	}

 	shdr->sh_name = 33; /* offset in shd_string_table */
 	shdr->sh_type = SHT_NOTE;
 	shdr->sh_addr = 0x0;
 	shdr->sh_flags = SHF_ALLOC;
 	shdr->sh_size = sizeof(bnote);
 	shdr->sh_entsize = 0;

 #ifdef HAVE_DWARF_SUPPORT
 	if (debug && nr_debug_entries) {
 		retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
 		if (retval)
 			goto error;
 	} else
 #endif
 	{
 		if (elf_update(e, ELF_C_WRITE) < 0) {
 			warnx("elf_update 4 failed");
 			goto error;
 		}
 	}

 	retval = 0;
 error:
 	(void)elf_end(e);

 	free(strsym);


 	return retval;
 }

 #ifndef JVMTI

 static unsigned char x86_code[] = {
     0xBB, 0x2A, 0x00, 0x00, 0x00, /* movl $42, %ebx */
     0xB8, 0x01, 0x00, 0x00, 0x00, /* movl $1, %eax */
     0xCD, 0x80            /* int $0x80 */
 };

 static struct options options;

 int main(int argc, char **argv)
 {
 	int c, fd, ret;

 	while ((c = getopt(argc, argv, "o:h")) != -1) {
 		switch (c) {
 		case 'o':
 			options.output = optarg;
 			break;
 		case 'h':
 			printf("Usage: genelf -o output_file [-h]\n");
 			return 0;
 		default:
 			errx(1, "unknown option");
 		}
 	}

 	fd = open(options.output, O_CREAT|O_TRUNC|O_RDWR, 0666);
 	if (fd == -1)
 		err(1, "cannot create file %s", options.output);

 	ret = jit_write_elf(fd, "main", x86_code, sizeof(x86_code));
 	close(fd);

 	if (ret != 0)
 		unlink(options.output);

 	return ret;
 }
 #endif
	/*
	* genelf.c
	* Copyright (C) 2014, Google, Inc
	*
	* Contributed by:
	* Stephane Eranian <eranian@gmail.com>
	*
	* Released under the GPL v2. (and only v2, not any later version)
	*/

	#include <sys/types.h>
	#include <stdio.h>
	#include <getopt.h>
	#include <stddef.h>
	#include <libelf.h>
	#include <string.h>
	#include <stdlib.h>
	#include <inttypes.h>
	#include <limits.h>
	#include <fcntl.h>
	#include <err.h>
	#ifdef HAVE_DWARF_SUPPORT
	#include <dwarf.h>
	#endif

	#include "perf.h"
	#include "genelf.h"
	#include "../util/jitdump.h"

	#ifndef NT_GNU_BUILD_ID
	#define NT_GNU_BUILD_ID 3
	#endif

	#define JVMTI

	#define BUILD_ID_URANDOM /* different uuid for each run */

	// FIXME, remove this and fix the deprecation warnings before its removed and
	// We'll break for good here...
	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"

	#ifdef HAVE_LIBCRYPTO_SUPPORT

	#define BUILD_ID_MD5
	#undef BUILD_ID_SHA /* does not seem to work well when linked with Java */
	#undef BUILD_ID_URANDOM /* different uuid for each run */

	#ifdef BUILD_ID_SHA
	#include <openssl/sha.h>
	#endif

	#ifdef BUILD_ID_MD5
	#include <openssl/md5.h>
	#endif
	#endif


	typedef struct {
	unsigned int namesz; /* Size of entry's owner string */
	unsigned int descsz; /* Size of the note descriptor */
	unsigned int type; /* Interpretation of the descriptor */
	char name[0]; /* Start of the name+desc data */
	} Elf_Note;

	struct options {
	char *output;
	int fd;
	};

	static char shd_string_table[] = {
	0,
	'.', 't', 'e', 'x', 't', 0, /* 1 */
	'.', 's', 'h', 's', 't', 'r', 't', 'a', 'b', 0, /* 7 */
	'.', 's', 'y', 'm', 't', 'a', 'b', 0, /* 17 */
	'.', 's', 't', 'r', 't', 'a', 'b', 0, /* 25 */
	'.', 'n', 'o', 't', 'e', '.', 'g', 'n', 'u', '.', 'b', 'u', 'i', 'l', 'd', '-', 'i', 'd', 0, /* 33 */
	'.', 'd', 'e', 'b', 'u', 'g', '_', 'l', 'i', 'n', 'e', 0, /* 52 */
	'.', 'd', 'e', 'b', 'u', 'g', '_', 'i', 'n', 'f', 'o', 0, /* 64 */
	'.', 'd', 'e', 'b', 'u', 'g', '_', 'a', 'b', 'b', 'r', 'e', 'v', 0, /* 76 */
	'.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', '_', 'h', 'd', 'r', 0, /* 90 */
	'.', 'e', 'h', '_', 'f', 'r', 'a', 'm', 'e', 0, /* 104 */
	};

	static struct buildid_note {
	Elf_Note desc; /* descsz: size of build-id, must be multiple of 4 */
	char name[4]; /* GNU\0 */
	char build_id[20];
	} bnote;

	static Elf_Sym symtab[]={
	/* symbol 0 MUST be the undefined symbol */
	{ .st_name = 0, /* index in sym_string table */
	.st_info = ELF_ST_TYPE(STT_NOTYPE),
	.st_shndx = 0, /* for now */
	.st_value = 0x0,
	.st_other = ELF_ST_VIS(STV_DEFAULT),
	.st_size = 0,
	},
	{ .st_name = 1, /* index in sym_string table */
	.st_info = ELF_ST_BIND(STB_LOCAL) \| ELF_ST_TYPE(STT_FUNC),
	.st_shndx = 1,
	.st_value = 0, /* for now */
	.st_other = ELF_ST_VIS(STV_DEFAULT),
	.st_size = 0, /* for now */
	}
	};

	#ifdef BUILD_ID_URANDOM
	static void
	gen_build_id(struct buildid_note *note,
	unsigned long load_addr __maybe_unused,
	const void *code __maybe_unused,
	size_t csize __maybe_unused)
	{
	int fd;
	size_t sz = sizeof(note->build_id);
	ssize_t sret;

	fd = open("/dev/urandom", O_RDONLY);
	if (fd == -1)
	err(1, "cannot access /dev/urandom for builid");

	sret = read(fd, note->build_id, sz);

	close(fd);

	if (sret != (ssize_t)sz)
	memset(note->build_id, 0, sz);
	}
	#endif

	#ifdef BUILD_ID_SHA
	static void
	gen_build_id(struct buildid_note *note,
	unsigned long load_addr __maybe_unused,
	const void *code,
	size_t csize)
	{
	if (sizeof(note->build_id) < SHA_DIGEST_LENGTH)
	errx(1, "build_id too small for SHA1");

	SHA1(code, csize, (unsigned char *)note->build_id);
	}
	#endif

	#ifdef BUILD_ID_MD5
	static void
	gen_build_id(struct buildid_note note, unsigned long load_addr, const void code, size_t csize)
	{
	MD5_CTX context;

	if (sizeof(note->build_id) < 16)
	errx(1, "build_id too small for MD5");

	MD5_Init(&context);
	MD5_Update(&context, &load_addr, sizeof(load_addr));
	MD5_Update(&context, code, csize);
	MD5_Final((unsigned char *)note->build_id, &context);
	}
	#endif

	static int
	jit_add_eh_frame_info(Elf e, void unwinding, uint64_t unwinding_header_size,
	uint64_t unwinding_size, uint64_t base_offset)
	{
	Elf_Data *d;
	Elf_Scn *scn;
	Elf_Shdr *shdr;
	uint64_t unwinding_table_size = unwinding_size - unwinding_header_size;

	/*
	* setup eh_frame section
	*/
	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	return -1;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	return -1;
	}

	d->d_align = 8;
	d->d_off = 0LL;
	d->d_buf = unwinding;
	d->d_type = ELF_T_BYTE;
	d->d_size = unwinding_table_size;
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	return -1;
	}

	shdr->sh_name = 104;
	shdr->sh_type = SHT_PROGBITS;
	shdr->sh_addr = base_offset;
	shdr->sh_flags = SHF_ALLOC;
	shdr->sh_entsize = 0;

	/*
	* setup eh_frame_hdr section
	*/
	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	return -1;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	return -1;
	}

	d->d_align = 4;
	d->d_off = 0LL;
	d->d_buf = unwinding + unwinding_table_size;
	d->d_type = ELF_T_BYTE;
	d->d_size = unwinding_header_size;
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	return -1;
	}

	shdr->sh_name = 90;
	shdr->sh_type = SHT_PROGBITS;
	shdr->sh_addr = base_offset + unwinding_table_size;
	shdr->sh_flags = SHF_ALLOC;
	shdr->sh_entsize = 0;

	return 0;
	}

	/*
	* fd: file descriptor open for writing for the output file
	* load_addr: code load address (could be zero, just used for buildid)
	* sym: function name (for native code - used as the symbol)
	* code: the native code
	* csize: the code size in bytes
	*/
	int
	jit_write_elf(int fd, uint64_t load_addr, const char *sym,
	const void *code, int csize,
	void *debug __maybe_unused, int nr_debug_entries __maybe_unused,
	void *unwinding, uint64_t unwinding_header_size, uint64_t unwinding_size)
	{
	Elf *e;
	Elf_Data *d;
	Elf_Scn *scn;
	Elf_Ehdr *ehdr;
	Elf_Shdr *shdr;
	uint64_t eh_frame_base_offset;
	char *strsym = NULL;
	int symlen;
	int retval = -1;

	if (elf_version(EV_CURRENT) == EV_NONE) {
	warnx("ELF initialization failed");
	return -1;
	}

	e = elf_begin(fd, ELF_C_WRITE, NULL);
	if (!e) {
	warnx("elf_begin failed");
	goto error;
	}

	/*
	* setup ELF header
	*/
	ehdr = elf_newehdr(e);
	if (!ehdr) {
	warnx("cannot get ehdr");
	goto error;
	}

	ehdr->e_ident[EI_DATA] = GEN_ELF_ENDIAN;
	ehdr->e_ident[EI_CLASS] = GEN_ELF_CLASS;
	ehdr->e_machine = GEN_ELF_ARCH;
	ehdr->e_type = ET_DYN;
	ehdr->e_entry = GEN_ELF_TEXT_OFFSET;
	ehdr->e_version = EV_CURRENT;
	ehdr->e_shstrndx= unwinding ? 4 : 2; /* shdr index for section name */

	/*
	* setup text section
	*/
	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	goto error;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	goto error;
	}

	d->d_align = 16;
	d->d_off = 0LL;
	d->d_buf = (void *)code;
	d->d_type = ELF_T_BYTE;
	d->d_size = csize;
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	goto error;
	}

	shdr->sh_name = 1;
	shdr->sh_type = SHT_PROGBITS;
	shdr->sh_addr = GEN_ELF_TEXT_OFFSET;
	shdr->sh_flags = SHF_EXECINSTR \| SHF_ALLOC;
	shdr->sh_entsize = 0;

	/*
	* Setup .eh_frame_hdr and .eh_frame
	*/
	if (unwinding) {
	eh_frame_base_offset = ALIGN_8(GEN_ELF_TEXT_OFFSET + csize);
	retval = jit_add_eh_frame_info(e, unwinding,
	unwinding_header_size, unwinding_size,
	eh_frame_base_offset);
	if (retval)
	goto error;
	}

	/*
	* setup section headers string table
	*/
	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	goto error;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	goto error;
	}

	d->d_align = 1;
	d->d_off = 0LL;
	d->d_buf = shd_string_table;
	d->d_type = ELF_T_BYTE;
	d->d_size = sizeof(shd_string_table);
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	goto error;
	}

	shdr->sh_name = 7; /* offset of '.shstrtab' in shd_string_table */
	shdr->sh_type = SHT_STRTAB;
	shdr->sh_flags = 0;
	shdr->sh_entsize = 0;

	/*
	* setup symtab section
	*/
	symtab[1].st_size = csize;
	symtab[1].st_value = GEN_ELF_TEXT_OFFSET;

	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	goto error;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	goto error;
	}

	d->d_align = 8;
	d->d_off = 0LL;
	d->d_buf = symtab;
	d->d_type = ELF_T_SYM;
	d->d_size = sizeof(symtab);
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	goto error;
	}

	shdr->sh_name = 17; /* offset of '.symtab' in shd_string_table */
	shdr->sh_type = SHT_SYMTAB;
	shdr->sh_flags = 0;
	shdr->sh_entsize = sizeof(Elf_Sym);
	shdr->sh_link = unwinding ? 6 : 4; /* index of .strtab section */

	/*
	* setup symbols string table
	* 2 = 1 for 0 in 1st entry, 1 for the 0 at end of symbol for 2nd entry
	*/
	symlen = 2 + strlen(sym);
	strsym = calloc(1, symlen);
	if (!strsym) {
	warnx("cannot allocate strsym");
	goto error;
	}
	strcpy(strsym + 1, sym);

	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	goto error;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	goto error;
	}

	d->d_align = 1;
	d->d_off = 0LL;
	d->d_buf = strsym;
	d->d_type = ELF_T_BYTE;
	d->d_size = symlen;
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	goto error;
	}

	shdr->sh_name = 25; /* offset in shd_string_table */
	shdr->sh_type = SHT_STRTAB;
	shdr->sh_flags = 0;
	shdr->sh_entsize = 0;

	/*
	* setup build-id section
	*/
	scn = elf_newscn(e);
	if (!scn) {
	warnx("cannot create section");
	goto error;
	}

	d = elf_newdata(scn);
	if (!d) {
	warnx("cannot get new data");
	goto error;
	}

	/*
	* build-id generation
	*/
	gen_build_id(&bnote, load_addr, code, csize);
	bnote.desc.namesz = sizeof(bnote.name); /* must include 0 termination */
	bnote.desc.descsz = sizeof(bnote.build_id);
	bnote.desc.type = NT_GNU_BUILD_ID;
	strcpy(bnote.name, "GNU");

	d->d_align = 4;
	d->d_off = 0LL;
	d->d_buf = &bnote;
	d->d_type = ELF_T_BYTE;
	d->d_size = sizeof(bnote);
	d->d_version = EV_CURRENT;

	shdr = elf_getshdr(scn);
	if (!shdr) {
	warnx("cannot get section header");
	goto error;
	}

	shdr->sh_name = 33; /* offset in shd_string_table */
	shdr->sh_type = SHT_NOTE;
	shdr->sh_addr = 0x0;
	shdr->sh_flags = SHF_ALLOC;
	shdr->sh_size = sizeof(bnote);
	shdr->sh_entsize = 0;

	#ifdef HAVE_DWARF_SUPPORT
	if (debug && nr_debug_entries) {
	retval = jit_add_debug_info(e, load_addr, debug, nr_debug_entries);
	if (retval)
	goto error;
	} else
	#endif
	{
	if (elf_update(e, ELF_C_WRITE) < 0) {
	warnx("elf_update 4 failed");
	goto error;
	}
	}

	retval = 0;
	error:
	(void)elf_end(e);

	free(strsym);


	return retval;
	}

	#ifndef JVMTI

	static unsigned char x86_code[] = {
	0xBB, 0x2A, 0x00, 0x00, 0x00, /* movl $42, %ebx */
	0xB8, 0x01, 0x00, 0x00, 0x00, /* movl $1, %eax */
	0xCD, 0x80 /* int $0x80 */
	};

	static struct options options;

	int main(int argc, char **argv)
	{
	int c, fd, ret;

	while ((c = getopt(argc, argv, "o:h")) != -1) {
	switch (c) {
	case 'o':
	options.output = optarg;
	break;
	case 'h':
	printf("Usage: genelf -o output_file [-h]\n");
	return 0;
	default:
	errx(1, "unknown option");
	}
	}

	fd = open(options.output, O_CREAT\|O_TRUNC\|O_RDWR, 0666);
	if (fd == -1)
	err(1, "cannot create file %s", options.output);

	ret = jit_write_elf(fd, "main", x86_code, sizeof(x86_code));
	close(fd);

	if (ret != 0)
	unlink(options.output);

	return ret;
	}
	#endif