path: root/scripts/recordmcount.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

#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;

	file_updated = 1;

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

		if (aoffset > file_append_size) {
			file_append = realloc(file_append, aoffset);
			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 -