/*
 * 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 <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 */

/* 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 ((off_t)-1 == w) {
                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 (0 == addr) {
                fprintf(stderr, "malloc failed: %zu bytes\n", size);
                fail_file();
        }
        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)
{
        void *addr;

        fd_map = open(fname, O_RDWR);
        if (0 > fd_map || 0 > fstat(fd_map, &sb)) {
                perror(fname);
                fail_file();
        }
        if (!S_ISREG(sb.st_mode)) {
                fprintf(stderr, "not a regular file: %s\n", fname);
                fail_file();
        }
        addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE,
                    fd_map, 0);
        mmap_failed = 0;
        if (MAP_FAILED == addr) {
                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 0 == strcmp(".text",          txtname) ||
                0 == strcmp(".sched.text",    txtname) ||
                0 == strcmp(".spinlock.text", txtname) ||
                0 == strcmp(".irqentry.text", txtname) ||
                0 == strcmp(".text.unlikely", txtname);
}

/* 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\n",
                        ehdr->e_ident[EI_DATA], fname);
                fail_file();
        } break;
        case ELFDATA2LSB: {
                if (1 != *(unsigned char const *)&endian) {
                        /* main() is big endian, file.o is little endian. */
                        w = w4rev;
                        w2 = w2rev;
                        w8 = w8rev;
                }
        } break;
        case ELFDATA2MSB: {
                if (0 != *(unsigned char const *)&endian) {
                        /* main() is little endian, file.o is big endian. */
                        w = w4rev;
                        w2 = w2rev;
                        w8 = w8rev;
                }
        } break;
        }  /* end switch */
        if (0 != memcmp(ELFMAG, ehdr->e_ident, SELFMAG)
        ||  ET_REL != w2(ehdr->e_type)
        ||  EV_CURRENT != ehdr->e_ident[EI_VERSION]) {
                fprintf(stderr, "unrecognized ET_REL file %s\n", fname);
                fail_file();
        }

        gpfx = 0;
        switch (w2(ehdr->e_machine)) {
        default: {
                fprintf(stderr, "unrecognized e_machine %d %s\n",
                        w2(ehdr->e_machine), fname);
                fail_file();
        } break;
        case EM_386:     reltype = R_386_32;                   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:  reltype = R_X86_64_64;                break;
        }  /* end switch */

        switch (ehdr->e_ident[EI_CLASS]) {
        default: {
                fprintf(stderr, "unrecognized ELF class %d %s\n",
                        ehdr->e_ident[EI_CLASS], fname);
                fail_file();
        } break;
        case ELFCLASS32: {
                if (sizeof(Elf32_Ehdr) != w2(ehdr->e_ehsize)
                ||  sizeof(Elf32_Shdr) != w2(ehdr->e_shentsize)) {
                        fprintf(stderr,
                                "unrecognized ET_REL file: %s\n", fname);
                        fail_file();
                }
                if (EM_S390 == w2(ehdr->e_machine))
                        reltype = R_390_32;
                if (EM_MIPS == w2(ehdr->e_machine)) {
                        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 (sizeof(Elf64_Ehdr) != w2(ghdr->e_ehsize)
                ||  sizeof(Elf64_Shdr) != w2(ghdr->e_shentsize)) {
                        fprintf(stderr,
                                "unrecognized ET_REL file: %s\n", fname);
                        fail_file();
                }
                if (EM_S390 == w2(ghdr->e_machine))
                        reltype = R_390_64;
                if (EM_MIPS == w2(ghdr->e_machine)) {
                        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 const *argv[])
{
        const char ftrace[] = "/ftrace.o";
        int ftrace_size = sizeof(ftrace) - 1;
        int n_error = 0;  /* gcc-4.3.0 false positive complaint */

        if (argc <= 1) {
                fprintf(stderr, "usage: recordmcount file.o...\n");
                return 0;
        }

        /* Process each file in turn, allowing deep failure. */
        for (--argc, ++argv; 0 < argc; --argc, ++argv) {
                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(argv[0]);
                if (len >= ftrace_size &&
                    strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
                        continue;

                switch (sjval) {
                default: {
                        fprintf(stderr, "internal error: %s\n", argv[0]);
                        exit(1);
                } break;
                case SJ_SETJMP: {  /* normal sequence */
                        /* Avoid problems if early cleanup() */
                        fd_map = -1;
                        ehdr_curr = NULL;
                        mmap_failed = 1;
                        do_file(argv[0]);
                } 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;
}