/*
   * recordmcount.c: construct a table of the locations of calls to 'mcount'
   * so that ftrace can find them quickly.
   * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>.  All rights reserved.
   * Licensed under the GNU General Public License, version 2 (GPLv2).
   *
   * Restructured to fit Linux format, as well as other updates:
   *  Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
   */
  
  /*
   * Strategy: alter the .o file in-place.
   *
   * Append a new STRTAB that has the new section names, followed by a new array
   * ElfXX_Shdr[] that has the new section headers, followed by the section
   * contents for __mcount_loc and its relocations.  The old shstrtab strings,
   * and the old ElfXX_Shdr[] array, remain as "garbage" (commonly, a couple
   * kilobytes.)  Subsequent processing by /bin/ld (or the kernel module loader)
   * will ignore the garbage regions, because they are not designated by the
   * new .e_shoff nor the new ElfXX_Shdr[].  [In order to remove the garbage,
   * then use "ld -r" to create a new file that omits the garbage.]
   */
  
  #include <sys/types.h>
  #include <sys/mman.h>
  #include <sys/stat.h>

  #include <getopt.h>

  #include <elf.h>
  #include <fcntl.h>
  #include <setjmp.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  
  static int fd_map;	/* File descriptor for file being modified. */
  static int mmap_failed; /* Boolean flag. */
  static void *ehdr_curr; /* current ElfXX_Ehdr *  for resource cleanup */
  static char gpfx;	/* prefix for global symbol name (sometimes '_') */
  static struct stat sb;	/* Remember .st_size, etc. */
  static jmp_buf jmpenv;	/* setjmp/longjmp per-file error escape */

  static const char *altmcount;	/* alternate mcount symbol name */

  static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */

  
  /* setjmp() return values */
  enum {
  	SJ_SETJMP = 0,  /* hardwired first return */
  	SJ_FAIL,
  	SJ_SUCCEED
  };
  
  /* Per-file resource cleanup when multiple files. */
  static void
  cleanup(void)
  {
  	if (!mmap_failed)
  		munmap(ehdr_curr, sb.st_size);
  	else
  		free(ehdr_curr);
  	close(fd_map);
  }
  
  static void __attribute__((noreturn))
  fail_file(void)
  {
  	cleanup();
  	longjmp(jmpenv, SJ_FAIL);
  }
  
  static void __attribute__((noreturn))
  succeed_file(void)
  {
  	cleanup();
  	longjmp(jmpenv, SJ_SUCCEED);
  }
  
  /* ulseek, uread, ...:  Check return value for errors. */
  
  static off_t
  ulseek(int const fd, off_t const offset, int const whence)
  {
  	off_t const w = lseek(fd, offset, whence);

  	if (w == (off_t)-1) {

  		perror("lseek");
  		fail_file();
  	}
  	return w;
  }
  
  static size_t
  uread(int const fd, void *const buf, size_t const count)
  {
  	size_t const n = read(fd, buf, count);
  	if (n != count) {
  		perror("read");
  		fail_file();
  	}
  	return n;
  }
  
  static size_t
  uwrite(int const fd, void const *const buf, size_t const count)
  {
  	size_t const n = write(fd, buf, count);
  	if (n != count) {
  		perror("write");
  		fail_file();
  	}
  	return n;
  }
  
  static void *
  umalloc(size_t size)
  {
  	void *const addr = malloc(size);

  	if (addr == 0) {

  		fprintf(stderr, "malloc failed: %zu bytes
  ", size);
  		fail_file();
  	}
  	return addr;
  }

  static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
  static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
  static unsigned char *ideal_nop;
  
  static char rel_type_nop;
  
  static int (*make_nop)(void *map, size_t const offset);
  
  static int make_nop_x86(void *map, size_t const offset)
  {
  	uint32_t *ptr;
  	unsigned char *op;
  
  	/* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
  	ptr = map + offset;
  	if (*ptr != 0)
  		return -1;
  
  	op = map + offset - 1;
  	if (*op != 0xe8)
  		return -1;
  
  	/* convert to nop */
  	ulseek(fd_map, offset - 1, SEEK_SET);
  	uwrite(fd_map, ideal_nop, 5);
  	return 0;
  }

  /*
   * Get the whole file as a programming convenience in order to avoid
   * malloc+lseek+read+free of many pieces.  If successful, then mmap
   * avoids copying unused pieces; else just read the whole file.
   * Open for both read and write; new info will be appended to the file.
   * Use MAP_PRIVATE so that a few changes to the in-memory ElfXX_Ehdr
   * do not propagate to the file until an explicit overwrite at the last.
   * This preserves most aspects of consistency (all except .st_size)
   * for simultaneous readers of the file while we are appending to it.
   * However, multiple writers still are bad.  We choose not to use
   * locking because it is expensive and the use case of kernel build
   * makes multiple writers unlikely.
   */
  static void *mmap_file(char const *fname)
  {
  	void *addr;
  
  	fd_map = open(fname, O_RDWR);

  	if (fd_map < 0 || fstat(fd_map, &sb) < 0) {

  		perror(fname);
  		fail_file();
  	}
  	if (!S_ISREG(sb.st_mode)) {
  		fprintf(stderr, "not a regular file: %s
  ", fname);
  		fail_file();
  	}
  	addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
  		    fd_map, 0);
  	mmap_failed = 0;

  	if (addr == MAP_FAILED) {

  		mmap_failed = 1;
  		addr = umalloc(sb.st_size);
  		uread(fd_map, addr, sb.st_size);
  	}
  	return addr;
  }
  
  /* w8rev, w8nat, ...: Handle endianness. */
  
  static uint64_t w8rev(uint64_t const x)
  {
  	return   ((0xff & (x >> (0 * 8))) << (7 * 8))
  	       | ((0xff & (x >> (1 * 8))) << (6 * 8))
  	       | ((0xff & (x >> (2 * 8))) << (5 * 8))
  	       | ((0xff & (x >> (3 * 8))) << (4 * 8))
  	       | ((0xff & (x >> (4 * 8))) << (3 * 8))
  	       | ((0xff & (x >> (5 * 8))) << (2 * 8))
  	       | ((0xff & (x >> (6 * 8))) << (1 * 8))
  	       | ((0xff & (x >> (7 * 8))) << (0 * 8));
  }
  
  static uint32_t w4rev(uint32_t const x)
  {
  	return   ((0xff & (x >> (0 * 8))) << (3 * 8))
  	       | ((0xff & (x >> (1 * 8))) << (2 * 8))
  	       | ((0xff & (x >> (2 * 8))) << (1 * 8))
  	       | ((0xff & (x >> (3 * 8))) << (0 * 8));
  }
  
  static uint32_t w2rev(uint16_t const x)
  {
  	return   ((0xff & (x >> (0 * 8))) << (1 * 8))
  	       | ((0xff & (x >> (1 * 8))) << (0 * 8));
  }
  
  static uint64_t w8nat(uint64_t const x)
  {
  	return x;
  }
  
  static uint32_t w4nat(uint32_t const x)
  {
  	return x;
  }
  
  static uint32_t w2nat(uint16_t const x)
  {
  	return x;
  }
  
  static uint64_t (*w8)(uint64_t);
  static uint32_t (*w)(uint32_t);
  static uint32_t (*w2)(uint16_t);
  
  /* Names of the sections that could contain calls to mcount. */
  static int
  is_mcounted_section_name(char const *const txtname)
  {

  	return strcmp(".text",           txtname) == 0 ||
  		strcmp(".ref.text",      txtname) == 0 ||
  		strcmp(".sched.text",    txtname) == 0 ||
  		strcmp(".spinlock.text", txtname) == 0 ||
  		strcmp(".irqentry.text", txtname) == 0 ||

  		strcmp(".kprobes.text", txtname) == 0 ||

  		strcmp(".text.unlikely", txtname) == 0;

  }

  /* 32 bit and 64 bit are very similar */
  #include "recordmcount.h"
  #define RECORD_MCOUNT_64
  #include "recordmcount.h"

  /* 64-bit EM_MIPS has weird ELF64_Rela.r_info.
   * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf
   * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40]
   * to imply the order of the members; the spec does not say so.
   *	typedef unsigned char Elf64_Byte;
   * fails on MIPS64 because their <elf.h> already has it!
   */
  
  typedef uint8_t myElf64_Byte;		/* Type for a 8-bit quantity.  */
  
  union mips_r_info {
  	Elf64_Xword r_info;
  	struct {
  		Elf64_Word r_sym;		/* Symbol index.  */
  		myElf64_Byte r_ssym;		/* Special symbol.  */
  		myElf64_Byte r_type3;		/* Third relocation.  */
  		myElf64_Byte r_type2;		/* Second relocation.  */
  		myElf64_Byte r_type;		/* First relocation.  */
  	} r_mips;
  };
  
  static uint64_t MIPS64_r_sym(Elf64_Rel const *rp)
  {
  	return w(((union mips_r_info){ .r_info = rp->r_info }).r_mips.r_sym);
  }
  
  static void MIPS64_r_info(Elf64_Rel *const rp, unsigned sym, unsigned type)
  {
  	rp->r_info = ((union mips_r_info){
  		.r_mips = { .r_sym = w(sym), .r_type = type }
  	}).r_info;
  }

  static void
  do_file(char const *const fname)
  {
  	Elf32_Ehdr *const ehdr = mmap_file(fname);
  	unsigned int reltype = 0;
  
  	ehdr_curr = ehdr;
  	w = w4nat;
  	w2 = w2nat;
  	w8 = w8nat;
  	switch (ehdr->e_ident[EI_DATA]) {
  		static unsigned int const endian = 1;

  	default:

  		fprintf(stderr, "unrecognized ELF data encoding %d: %s
  ",
  			ehdr->e_ident[EI_DATA], fname);
  		fail_file();

  		break;
  	case ELFDATA2LSB:

  		if (*(unsigned char const *)&endian != 1) {

  			/* main() is big endian, file.o is little endian. */
  			w = w4rev;
  			w2 = w2rev;
  			w8 = w8rev;
  		}

  		break;
  	case ELFDATA2MSB:

  		if (*(unsigned char const *)&endian != 0) {

  			/* main() is little endian, file.o is big endian. */
  			w = w4rev;
  			w2 = w2rev;
  			w8 = w8rev;
  		}

  		break;

  	}  /* end switch */

  	if (memcmp(ELFMAG, ehdr->e_ident, SELFMAG) != 0
  	||  w2(ehdr->e_type) != ET_REL
  	||  ehdr->e_ident[EI_VERSION] != EV_CURRENT) {

  		fprintf(stderr, "unrecognized ET_REL file %s
  ", fname);
  		fail_file();
  	}
  
  	gpfx = 0;
  	switch (w2(ehdr->e_machine)) {

  	default:

  		fprintf(stderr, "unrecognized e_machine %d %s
  ",
  			w2(ehdr->e_machine), fname);
  		fail_file();

  		break;

  	case EM_386:
  		reltype = R_386_32;
  		make_nop = make_nop_x86;
  		ideal_nop = ideal_nop5_x86_32;

  		mcount_adjust_32 = -1;

  		break;

  	case EM_ARM:	 reltype = R_ARM_ABS32;
  			 altmcount = "__gnu_mcount_nc";
  			 break;

  	case EM_IA_64:	 reltype = R_IA64_IMM64;   gpfx = '_'; break;

  	case EM_MIPS:	 /* reltype: e_class    */ gpfx = '_'; break;

  	case EM_PPC:	 reltype = R_PPC_ADDR32;   gpfx = '_'; break;
  	case EM_PPC64:	 reltype = R_PPC64_ADDR64; gpfx = '_'; break;
  	case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
  	case EM_SH:	 reltype = R_SH_DIR32;                 break;
  	case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;

  	case EM_X86_64:
  		make_nop = make_nop_x86;
  		ideal_nop = ideal_nop5_x86_64;
  		reltype = R_X86_64_64;

  		mcount_adjust_64 = -1;

  		break;

  	}  /* end switch */
  
  	switch (ehdr->e_ident[EI_CLASS]) {

  	default:

  		fprintf(stderr, "unrecognized ELF class %d %s
  ",
  			ehdr->e_ident[EI_CLASS], fname);
  		fail_file();

  		break;
  	case ELFCLASS32:

  		if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
  		||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {

  			fprintf(stderr,
  				"unrecognized ET_REL file: %s
  ", fname);
  			fail_file();
  		}

  		if (w2(ehdr->e_machine) == EM_S390) {

  			reltype = R_390_32;

  			mcount_adjust_32 = -4;
  		}

  		if (w2(ehdr->e_machine) == EM_MIPS) {

  			reltype = R_MIPS_32;

  			is_fake_mcount32 = MIPS32_is_fake_mcount;
  		}

  		do32(ehdr, fname, reltype);

  		break;

  	case ELFCLASS64: {
  		Elf64_Ehdr *const ghdr = (Elf64_Ehdr *)ehdr;

  		if (w2(ghdr->e_ehsize) != sizeof(Elf64_Ehdr)
  		||  w2(ghdr->e_shentsize) != sizeof(Elf64_Shdr)) {

  			fprintf(stderr,
  				"unrecognized ET_REL file: %s
  ", fname);
  			fail_file();
  		}

  		if (w2(ghdr->e_machine) == EM_S390) {

  			reltype = R_390_64;

  			mcount_adjust_64 = -8;
  		}

  		if (w2(ghdr->e_machine) == EM_MIPS) {

  			reltype = R_MIPS_64;
  			Elf64_r_sym = MIPS64_r_sym;
  			Elf64_r_info = MIPS64_r_info;

  			is_fake_mcount64 = MIPS64_is_fake_mcount;

  		}

  		do64(ghdr, fname, reltype);

  		break;
  	}

  	}  /* end switch */
  
  	cleanup();
  }
  
  int

  main(int argc, char *argv[])

  {

  	const char ftrace[] = "/ftrace.o";

  	int ftrace_size = sizeof(ftrace) - 1;

  	int n_error = 0;  /* gcc-4.3.0 false positive complaint */

  	int c;
  	int i;

  	while ((c = getopt(argc, argv, "w")) >= 0) {
  		switch (c) {
  		case 'w':
  			warn_on_notrace_sect = 1;
  			break;
  		default:
  			fprintf(stderr, "usage: recordmcount [-w] file.o...
  ");
  			return 0;
  		}
  	}
  
  	if ((argc - optind) < 1) {
  		fprintf(stderr, "usage: recordmcount [-w] file.o...
  ");

  		return 0;
  	}
  
  	/* Process each file in turn, allowing deep failure. */

  	for (i = optind; i < argc; i++) {
  		char *file = argv[i];

  		int const sjval = setjmp(jmpenv);

  		int len;
  
  		/*
  		 * The file kernel/trace/ftrace.o references the mcount
  		 * function but does not call it. Since ftrace.o should
  		 * not be traced anyway, we just skip it.
  		 */

  		len = strlen(file);

  		if (len >= ftrace_size &&

  		    strcmp(file + (len - ftrace_size), ftrace) == 0)

  			continue;

  		switch (sjval) {

  		default:

  			fprintf(stderr, "internal error: %s
  ", file);

  			exit(1);

  			break;
  		case SJ_SETJMP:    /* normal sequence */

  			/* Avoid problems if early cleanup() */
  			fd_map = -1;
  			ehdr_curr = NULL;
  			mmap_failed = 1;

  			do_file(file);

  			break;
  		case SJ_FAIL:    /* error in do_file or below */

  			++n_error;

  			break;
  		case SJ_SUCCEED:    /* premature success */

  			/* do nothing */

  			break;

  		}  /* end switch */
  	}
  	return !!n_error;
  }