Quelle recordmcount.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
* 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.
*
* 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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifndef EM_AARCH64
#define EM_AARCH64 183
#define R_AARCH64_NONE  0
#define R_AARCH64_ABS64 257
#endif

#ifndef EM_LOONGARCH
#define EM_LOONGARCH  258
#define R_LARCH_32   1
#define R_LARCH_64   2
#define R_LARCH_MARK_LA   20
#define R_LARCH_SOP_PUSH_PLT_PCREL 29
#endif

#define R_ARM_PC24  1
#define R_ARM_THM_CALL  10
#define R_ARM_CALL  28

#define R_AARCH64_CALL26 283

static int fd_map; /* File descriptor for file being modified. */
static int mmap_failed; /* Boolean flag. */
static char gpfx; /* prefix for global symbol name (sometimes '_') */
static struct stat sb; /* Remember .st_size, etc. */
static const char *altmcount; /* alternate mcount symbol name */
static int warn_on_notrace_sect; /* warn when section has mcount not being recorded */
static void *file_map; /* pointer of the mapped file */
static void *file_end; /* pointer to the end of the mapped file */
static int file_updated; /* flag to state file was changed */
static void *file_ptr; /* current file pointer location */

static void *file_append; /* added to the end of the file */
static size_t file_append_size; /* how much is added to end of file */

/* Per-file resource cleanup when multiple files. */
static void file_append_cleanup(void)
{
free(file_append);
file_append = NULL;
file_append_size = 0;
file_updated = 0;
}

static void mmap_cleanup(void)
{
if (!mmap_failed)
  munmap(file_map, sb.st_size);
else
  free(file_map);
file_map = NULL;
}

/* ulseek, uwrite, ...:  Check return value for errors. */

static off_t ulseek(off_t const offset, int const whence)
{
switch (whence) {
case SEEK_SET:
  file_ptr = file_map + offset;
  break;
case SEEK_CUR:
  file_ptr += offset;
  break;
case SEEK_END:
  file_ptr = file_map + (sb.st_size - offset);
  break;
}
if (file_ptr < file_map) {
  fprintf(stderr, "lseek: seek before file\n");
  return -1;
}
return file_ptr - file_map;
}

static ssize_t uwrite(void const *const buf, size_t const count)
{
size_t cnt = count;
off_t idx = 0;
void *p = NULL;

file_updated = 1;

if (file_ptr + count >= file_end) {
  off_t aoffset = (file_ptr + count) - file_end;

  if (aoffset > file_append_size) {
   p = realloc(file_append, aoffset);
   if (!p)
    free(file_append);
   file_append = p;
   file_append_size = aoffset;
  }
  if (!file_append) {
   perror("write");
   file_append_cleanup();
   mmap_cleanup();
   return -1;
  }
  if (file_ptr < file_end) {
   cnt = file_end - file_ptr;
  } else {
   cnt = 0;
   idx = aoffset - count;
  }
}

if (cnt)
  memcpy(file_ptr, buf, cnt);

if (cnt < count)
  memcpy(file_append + idx, buf + cnt, count - cnt);

file_ptr += count;
return count;
}

static void * umalloc(size_t size)
{
void *const addr = malloc(size);
if (addr == 0) {
  fprintf(stderr, "malloc failed: %zu bytes\n", size);
  file_append_cleanup();
  mmap_cleanup();
  return NULL;
}
return addr;
}

/*
* 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)
{
/* Avoid problems if early cleanup() */
fd_map = -1;
mmap_failed = 1;
file_map = NULL;
file_ptr = NULL;
file_updated = 0;
sb.st_size = 0;

fd_map = open(fname, O_RDONLY);
if (fd_map < 0) {
  perror(fname);
  return NULL;
}
if (fstat(fd_map, &sb) < 0) {
  perror(fname);
  goto out;
}
if (!S_ISREG(sb.st_mode)) {
  fprintf(stderr, "not a regular file: %s\n", fname);
  goto out;
}
file_map = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
   fd_map, 0);
if (file_map == MAP_FAILED) {
  mmap_failed = 1;
  file_map = umalloc(sb.st_size);
  if (!file_map) {
   perror(fname);
   goto out;
  }
  if (read(fd_map, file_map, sb.st_size) != sb.st_size) {
   perror(fname);
   free(file_map);
   file_map = NULL;
   goto out;
  }
} else
  mmap_failed = 0;
out:
close(fd_map);
fd_map = -1;

file_end = file_map + sb.st_size;

return file_map;
}

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 */
if (ulseek(offset - 1, SEEK_SET) < 0)
  return -1;
if (uwrite(ideal_nop, 5) < 0)
  return -1;
return 0;
}

static unsigned char ideal_nop4_arm_le[4] = { 0x00, 0x00, 0xa0, 0xe1 }; /* mov r0, r0 */
static unsigned char ideal_nop4_arm_be[4] = { 0xe1, 0xa0, 0x00, 0x00 }; /* mov r0, r0 */
static unsigned char *ideal_nop4_arm;

static unsigned char bl_mcount_arm_le[4] = { 0xfe, 0xff, 0xff, 0xeb }; /* bl */
static unsigned char bl_mcount_arm_be[4] = { 0xeb, 0xff, 0xff, 0xfe }; /* bl */
static unsigned char *bl_mcount_arm;

static unsigned char push_arm_le[4] = { 0x04, 0xe0, 0x2d, 0xe5 }; /* push {lr} */
static unsigned char push_arm_be[4] = { 0xe5, 0x2d, 0xe0, 0x04 }; /* push {lr} */
static unsigned char *push_arm;

static unsigned char ideal_nop2_thumb_le[2] = { 0x00, 0xbf }; /* nop */
static unsigned char ideal_nop2_thumb_be[2] = { 0xbf, 0x00 }; /* nop */
static unsigned char *ideal_nop2_thumb;

static unsigned char push_bl_mcount_thumb_le[6] = { 0x00, 0xb5, 0xff, 0xf7, 0xfe, 0xff }; /* push {lr}, bl */
static unsigned char push_bl_mcount_thumb_be[6] = { 0xb5, 0x00, 0xf7, 0xff, 0xff, 0xfe }; /* push {lr}, bl */
static unsigned char *push_bl_mcount_thumb;

static int make_nop_arm(void *map, size_t const offset)
{
char *ptr;
int cnt = 1;
int nop_size;
size_t off = offset;

ptr = map + offset;
if (memcmp(ptr, bl_mcount_arm, 4) == 0) {
  if (memcmp(ptr - 4, push_arm, 4) == 0) {
   off -= 4;
   cnt = 2;
  }
  ideal_nop = ideal_nop4_arm;
  nop_size = 4;
} else if (memcmp(ptr - 2, push_bl_mcount_thumb, 6) == 0) {
  cnt = 3;
  nop_size = 2;
  off -= 2;
  ideal_nop = ideal_nop2_thumb;
} else
  return -1;

/* Convert to nop */
if (ulseek(off, SEEK_SET) < 0)
  return -1;

do {
  if (uwrite(ideal_nop, nop_size) < 0)
   return -1;
} while (--cnt > 0);

return 0;
}

static unsigned char ideal_nop4_arm64[4] = {0x1f, 0x20, 0x03, 0xd5};
static int make_nop_arm64(void *map, size_t const offset)
{
uint32_t *ptr;

ptr = map + offset;
/* bl <_mcount> is 0x94000000 before relocation */
if (*ptr != 0x94000000)
  return -1;

/* Convert to nop */
if (ulseek(offset, SEEK_SET) < 0)
  return -1;
if (uwrite(ideal_nop, 4) < 0)
  return -1;
return 0;
}

static int write_file(const char *fname)
{
char tmp_file[strlen(fname) + 4];
size_t n;

if (!file_updated)
  return 0;

sprintf(tmp_file, "%s.rc", fname);

/*
* After reading the entire file into memory, delete it
* and write it back, to prevent weird side effects of modifying
* an object file in place.
*/
fd_map = open(tmp_file, O_WRONLY | O_TRUNC | O_CREAT, sb.st_mode);
if (fd_map < 0) {
  perror(fname);
  return -1;
}
n = write(fd_map, file_map, sb.st_size);
if (n != sb.st_size) {
  perror("write");
  close(fd_map);
  return -1;
}
if (file_append_size) {
  n = write(fd_map, file_append, file_append_size);
  if (n != file_append_size) {
   perror("write");
   close(fd_map);
   return -1;
  }
}
close(fd_map);
if (rename(tmp_file, fname) < 0) {
  perror(fname);
  return -1;
}
return 0;
}

/* 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 strncmp(".text",          txtname, 5) == 0 ||
  strcmp(".init.text",     txtname) == 0 ||
  strcmp(".ref.text",      txtname) == 0 ||
  strcmp(".sched.text",    txtname) == 0 ||
  strcmp(".spinlock.text", txtname) == 0 ||
  strcmp(".irqentry.text", txtname) == 0 ||
  strcmp(".softirqentry.text", txtname) == 0 ||
  strcmp(".kprobes.text", txtname) == 0 ||
  strcmp(".cpuidle.text", txtname) == 0;
}

static char const *already_has_rel_mcount = "success"; /* our work here is done! */

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

static int arm_is_fake_mcount(Elf32_Rel const *rp)
{
switch (ELF32_R_TYPE(w(rp->r_info))) {
case R_ARM_THM_CALL:
case R_ARM_CALL:
case R_ARM_PC24:
  return 0;
}

return 1;
}

static int arm64_is_fake_mcount(Elf64_Rel const *rp)
{
return ELF64_R_TYPE(w8(rp->r_info)) != R_AARCH64_CALL26;
}

static int LARCH32_is_fake_mcount(Elf32_Rel const *rp)
{
switch (ELF64_R_TYPE(w(rp->r_info))) {
case R_LARCH_MARK_LA:
case R_LARCH_SOP_PUSH_PLT_PCREL:
  return 0;
}

return 1;
}

static int LARCH64_is_fake_mcount(Elf64_Rel const *rp)
{
switch (ELF64_R_TYPE(w(rp->r_info))) {
case R_LARCH_MARK_LA:
case R_LARCH_SOP_PUSH_PLT_PCREL:
  return 0;
}

return 1;
}

/* 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 int do_file(char const *const fname)
{
unsigned int reltype = 0;
Elf32_Ehdr *ehdr;
int rc = -1;

ehdr = mmap_file(fname);
if (!ehdr)
  goto out;

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\n",
   ehdr->e_ident[EI_DATA], fname);
  goto out;
case ELFDATA2LSB:
  if (*(unsigned char const *)&endian != 1) {
   /* main() is big endian, file.o is little endian. */
   w = w4rev;
   w2 = w2rev;
   w8 = w8rev;
  }
  ideal_nop4_arm = ideal_nop4_arm_le;
  bl_mcount_arm = bl_mcount_arm_le;
  push_arm = push_arm_le;
  ideal_nop2_thumb = ideal_nop2_thumb_le;
  push_bl_mcount_thumb = push_bl_mcount_thumb_le;
  break;
case ELFDATA2MSB:
  if (*(unsigned char const *)&endian != 0) {
   /* main() is little endian, file.o is big endian. */
   w = w4rev;
   w2 = w2rev;
   w8 = w8rev;
  }
  ideal_nop4_arm = ideal_nop4_arm_be;
  bl_mcount_arm = bl_mcount_arm_be;
  push_arm = push_arm_be;
  ideal_nop2_thumb = ideal_nop2_thumb_be;
  push_bl_mcount_thumb = push_bl_mcount_thumb_be;
  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\n", fname);
  goto out;
}

gpfx = '_';
switch (w2(ehdr->e_machine)) {
default:
  fprintf(stderr, "unrecognized e_machine %u %s\n",
   w2(ehdr->e_machine), fname);
  goto out;
case EM_386:
  reltype = R_386_32;
  rel_type_nop = R_386_NONE;
  make_nop = make_nop_x86;
  ideal_nop = ideal_nop5_x86_32;
  mcount_adjust_32 = -1;
  gpfx = 0;
  break;
case EM_ARM:
  reltype = R_ARM_ABS32;
  altmcount = "__gnu_mcount_nc";
  make_nop = make_nop_arm;
  rel_type_nop = R_ARM_NONE;
  is_fake_mcount32 = arm_is_fake_mcount;
  gpfx = 0;
  break;
case EM_AARCH64:
  reltype = R_AARCH64_ABS64;
  make_nop = make_nop_arm64;
  rel_type_nop = R_AARCH64_NONE;
  ideal_nop = ideal_nop4_arm64;
  is_fake_mcount64 = arm64_is_fake_mcount;
  break;
case EM_MIPS: /* reltype: e_class    */ break;
case EM_LOONGARCH: /* reltype: e_class    */ break;
case EM_PPC: reltype = R_PPC_ADDR32; break;
case EM_PPC64: reltype = R_PPC64_ADDR64; break;
case EM_S390: /* reltype: e_class    */ break;
case EM_SH: reltype = R_SH_DIR32; gpfx = 0; break;
case EM_SPARCV9: reltype = R_SPARC_64; break;
case EM_X86_64:
  make_nop = make_nop_x86;
  ideal_nop = ideal_nop5_x86_64;
  reltype = R_X86_64_64;
  rel_type_nop = R_X86_64_NONE;
  mcount_adjust_64 = -1;
  gpfx = 0;
  break;
}  /* end switch */

switch (ehdr->e_ident[EI_CLASS]) {
default:
  fprintf(stderr, "unrecognized ELF class %d %s\n",
   ehdr->e_ident[EI_CLASS], fname);
  goto out;
case ELFCLASS32:
  if (w2(ehdr->e_ehsize) != sizeof(Elf32_Ehdr)
  ||  w2(ehdr->e_shentsize) != sizeof(Elf32_Shdr)) {
   fprintf(stderr,
    "unrecognized ET_REL file: %s\n", fname);
   goto out;
  }
  if (w2(ehdr->e_machine) == EM_MIPS) {
   reltype = R_MIPS_32;
   is_fake_mcount32 = MIPS32_is_fake_mcount;
  }
  if (w2(ehdr->e_machine) == EM_LOONGARCH) {
   reltype = R_LARCH_32;
   is_fake_mcount32 = LARCH32_is_fake_mcount;
  }
  if (do32(ehdr, fname, reltype) < 0)
   goto out;
  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\n", fname);
   goto out;
  }
  if (w2(ghdr->e_machine) == EM_S390) {
   reltype = R_390_64;
   mcount_adjust_64 = -14;
  }
  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;
  }
  if (w2(ghdr->e_machine) == EM_LOONGARCH) {
   reltype = R_LARCH_64;
   is_fake_mcount64 = LARCH64_is_fake_mcount;
  }
  if (do64(ghdr, fname, reltype) < 0)
   goto out;
  break;
}
}  /* end switch */

rc = write_file(fname);
out:
file_append_cleanup();
mmap_cleanup();
return rc;
}

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...\n");
   return 0;
  }
}

if ((argc - optind) < 1) {
  fprintf(stderr, "usage: recordmcount [-w] file.o...\n");
  return 0;
}

/* Process each file in turn, allowing deep failure. */
for (i = optind; i < argc; i++) {
  char *file = argv[i];
  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;

  if (do_file(file)) {
   fprintf(stderr, "%s: failed\n", file);
   ++n_error;
  }
}
return !!n_error;
}

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