root/scripts/recordmcount.h

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INCLUDED FROM

DEFINITIONS

This source file includes following definitions.
  1. fn_is_fake_mcount
  2. fn_ELF_R_SYM
  3. fn_ELF_R_INFO
  4. MIPS_is_fake_mcount
  5. append_func
  6. get_mcountsym
  7. get_sym_str_and_relp
  8. sift_rel_mcount
  9. nop_mcount
  10. find_secsym_ndx
  11. __has_rel_mcount
  12. has_rel_mcount
  13. tot_relsize
  14. do_func
/*
 * recordmcount.h
 *
 * This code was taken out of recordmcount.c written by
 * Copyright 2009 John F. Reiser <jreiser@BitWagon.com>.  All rights reserved.
 *
 * The original code had the same algorithms for both 32bit
 * and 64bit ELF files, but the code was duplicated to support
 * the difference in structures that were used. This
 * file creates a macro of everything that is different between
 * the 64 and 32 bit code, such that by including this header
 * twice we can create both sets of functions by including this
 * header once with RECORD_MCOUNT_64 undefined, and again with
 * it defined.
 *
 * This conversion to macros was done by:
 * Copyright 2010 Steven Rostedt <srostedt@redhat.com>, Red Hat Inc.
 *
 * Licensed under the GNU General Public License, version 2 (GPLv2).
 */
#undef append_func
#undef is_fake_mcount
#undef fn_is_fake_mcount
#undef MIPS_is_fake_mcount
#undef mcount_adjust
#undef sift_rel_mcount
#undef nop_mcount
#undef find_secsym_ndx
#undef __has_rel_mcount
#undef has_rel_mcount
#undef tot_relsize
#undef get_mcountsym
#undef get_sym_str_and_relp
#undef do_func
#undef Elf_Addr
#undef Elf_Ehdr
#undef Elf_Shdr
#undef Elf_Rel
#undef Elf_Rela
#undef Elf_Sym
#undef ELF_R_SYM
#undef Elf_r_sym
#undef ELF_R_INFO
#undef Elf_r_info
#undef ELF_ST_BIND
#undef ELF_ST_TYPE
#undef fn_ELF_R_SYM
#undef fn_ELF_R_INFO
#undef uint_t
#undef _w
#undef _align
#undef _size

#ifdef RECORD_MCOUNT_64
# define append_func            append64
# define sift_rel_mcount        sift64_rel_mcount
# define nop_mcount             nop_mcount_64
# define find_secsym_ndx        find64_secsym_ndx
# define __has_rel_mcount       __has64_rel_mcount
# define has_rel_mcount         has64_rel_mcount
# define tot_relsize            tot64_relsize
# define get_sym_str_and_relp   get_sym_str_and_relp_64
# define do_func                do64
# define get_mcountsym          get_mcountsym_64
# define is_fake_mcount         is_fake_mcount64
# define fn_is_fake_mcount      fn_is_fake_mcount64
# define MIPS_is_fake_mcount    MIPS64_is_fake_mcount
# define mcount_adjust          mcount_adjust_64
# define Elf_Addr               Elf64_Addr
# define Elf_Ehdr               Elf64_Ehdr
# define Elf_Shdr               Elf64_Shdr
# define Elf_Rel                Elf64_Rel
# define Elf_Rela               Elf64_Rela
# define Elf_Sym                Elf64_Sym
# define ELF_R_SYM              ELF64_R_SYM
# define Elf_r_sym              Elf64_r_sym
# define ELF_R_INFO             ELF64_R_INFO
# define Elf_r_info             Elf64_r_info
# define ELF_ST_BIND            ELF64_ST_BIND
# define ELF_ST_TYPE            ELF64_ST_TYPE
# define fn_ELF_R_SYM           fn_ELF64_R_SYM
# define fn_ELF_R_INFO          fn_ELF64_R_INFO
# define uint_t                 uint64_t
# define _w                     w8
# define _align                 7u
# define _size                  8
#else
# define append_func            append32
# define sift_rel_mcount        sift32_rel_mcount
# define nop_mcount             nop_mcount_32
# define find_secsym_ndx        find32_secsym_ndx
# define __has_rel_mcount       __has32_rel_mcount
# define has_rel_mcount         has32_rel_mcount
# define tot_relsize            tot32_relsize
# define get_sym_str_and_relp   get_sym_str_and_relp_32
# define do_func                do32
# define get_mcountsym          get_mcountsym_32
# define is_fake_mcount         is_fake_mcount32
# define fn_is_fake_mcount      fn_is_fake_mcount32
# define MIPS_is_fake_mcount    MIPS32_is_fake_mcount
# define mcount_adjust          mcount_adjust_32
# define Elf_Addr               Elf32_Addr
# define Elf_Ehdr               Elf32_Ehdr
# define Elf_Shdr               Elf32_Shdr
# define Elf_Rel                Elf32_Rel
# define Elf_Rela               Elf32_Rela
# define Elf_Sym                Elf32_Sym
# define ELF_R_SYM              ELF32_R_SYM
# define Elf_r_sym              Elf32_r_sym
# define ELF_R_INFO             ELF32_R_INFO
# define Elf_r_info             Elf32_r_info
# define ELF_ST_BIND            ELF32_ST_BIND
# define ELF_ST_TYPE            ELF32_ST_TYPE
# define fn_ELF_R_SYM           fn_ELF32_R_SYM
# define fn_ELF_R_INFO          fn_ELF32_R_INFO
# define uint_t                 uint32_t
# define _w                     w
# define _align                 3u
# define _size                  4
#endif

/* Functions and pointers that do_file() may override for specific e_machine. */
static int fn_is_fake_mcount(Elf_Rel const *rp)
{
        return 0;
}
static int (*is_fake_mcount)(Elf_Rel const *rp) = fn_is_fake_mcount;

static uint_t fn_ELF_R_SYM(Elf_Rel const *rp)
{
        return ELF_R_SYM(_w(rp->r_info));
}
static uint_t (*Elf_r_sym)(Elf_Rel const *rp) = fn_ELF_R_SYM;

static void fn_ELF_R_INFO(Elf_Rel *const rp, unsigned sym, unsigned type)
{
        rp->r_info = _w(ELF_R_INFO(sym, type));
}
static void (*Elf_r_info)(Elf_Rel *const rp, unsigned sym, unsigned type) = fn_ELF_R_INFO;

static int mcount_adjust = 0;

/*
 * MIPS mcount long call has 2 _mcount symbols, only the position of the 1st
 * _mcount symbol is needed for dynamic function tracer, with it, to disable
 * tracing(ftrace_make_nop), the instruction in the position is replaced with
 * the "b label" instruction, to enable tracing(ftrace_make_call), replace the
 * instruction back. So, here, we set the 2nd one as fake and filter it.
 *
 * c:   3c030000        lui     v1,0x0          <-->    b       label
 *              c: R_MIPS_HI16  _mcount
 *              c: R_MIPS_NONE  *ABS*
 *              c: R_MIPS_NONE  *ABS*
 * 10:  64630000        daddiu  v1,v1,0
 *              10: R_MIPS_LO16 _mcount
 *              10: R_MIPS_NONE *ABS*
 *              10: R_MIPS_NONE *ABS*
 * 14:  03e0082d        move    at,ra
 * 18:  0060f809        jalr    v1
 * label:
 */
#define MIPS_FAKEMCOUNT_OFFSET  4

static int MIPS_is_fake_mcount(Elf_Rel const *rp)
{
        static Elf_Addr old_r_offset = ~(Elf_Addr)0;
        Elf_Addr current_r_offset = _w(rp->r_offset);
        int is_fake;

        is_fake = (old_r_offset != ~(Elf_Addr)0) &&
                (current_r_offset - old_r_offset == MIPS_FAKEMCOUNT_OFFSET);
        old_r_offset = current_r_offset;

        return is_fake;
}

/* Append the new shstrtab, Elf_Shdr[], __mcount_loc and its relocations. */
static void append_func(Elf_Ehdr *const ehdr,
                        Elf_Shdr *const shstr,
                        uint_t const *const mloc0,
                        uint_t const *const mlocp,
                        Elf_Rel const *const mrel0,
                        Elf_Rel const *const mrelp,
                        unsigned int const rel_entsize,
                        unsigned int const symsec_sh_link)
{
        /* Begin constructing output file */
        Elf_Shdr mcsec;
        char const *mc_name = (sizeof(Elf_Rela) == rel_entsize)
                ? ".rela__mcount_loc"
                :  ".rel__mcount_loc";
        unsigned const old_shnum = w2(ehdr->e_shnum);
        uint_t const old_shoff = _w(ehdr->e_shoff);
        uint_t const old_shstr_sh_size   = _w(shstr->sh_size);
        uint_t const old_shstr_sh_offset = _w(shstr->sh_offset);
        uint_t t = 1 + strlen(mc_name) + _w(shstr->sh_size);
        uint_t new_e_shoff;

        shstr->sh_size = _w(t);
        shstr->sh_offset = _w(sb.st_size);
        t += sb.st_size;
        t += (_align & -t);  /* word-byte align */
        new_e_shoff = t;

        /* body for new shstrtab */
        ulseek(fd_map, sb.st_size, SEEK_SET);
        uwrite(fd_map, old_shstr_sh_offset + (void *)ehdr, old_shstr_sh_size);
        uwrite(fd_map, mc_name, 1 + strlen(mc_name));

        /* old(modified) Elf_Shdr table, word-byte aligned */
        ulseek(fd_map, t, SEEK_SET);
        t += sizeof(Elf_Shdr) * old_shnum;
        uwrite(fd_map, old_shoff + (void *)ehdr,
               sizeof(Elf_Shdr) * old_shnum);

        /* new sections __mcount_loc and .rel__mcount_loc */
        t += 2*sizeof(mcsec);
        mcsec.sh_name = w((sizeof(Elf_Rela) == rel_entsize) + strlen(".rel")
                + old_shstr_sh_size);
        mcsec.sh_type = w(SHT_PROGBITS);
        mcsec.sh_flags = _w(SHF_ALLOC);
        mcsec.sh_addr = 0;
        mcsec.sh_offset = _w(t);
        mcsec.sh_size = _w((void *)mlocp - (void *)mloc0);
        mcsec.sh_link = 0;
        mcsec.sh_info = 0;
        mcsec.sh_addralign = _w(_size);
        mcsec.sh_entsize = _w(_size);
        uwrite(fd_map, &mcsec, sizeof(mcsec));

        mcsec.sh_name = w(old_shstr_sh_size);
        mcsec.sh_type = (sizeof(Elf_Rela) == rel_entsize)
                ? w(SHT_RELA)
                : w(SHT_REL);
        mcsec.sh_flags = 0;
        mcsec.sh_addr = 0;
        mcsec.sh_offset = _w((void *)mlocp - (void *)mloc0 + t);
        mcsec.sh_size   = _w((void *)mrelp - (void *)mrel0);
        mcsec.sh_link = w(symsec_sh_link);
        mcsec.sh_info = w(old_shnum);
        mcsec.sh_addralign = _w(_size);
        mcsec.sh_entsize = _w(rel_entsize);
        uwrite(fd_map, &mcsec, sizeof(mcsec));

        uwrite(fd_map, mloc0, (void *)mlocp - (void *)mloc0);
        uwrite(fd_map, mrel0, (void *)mrelp - (void *)mrel0);

        ehdr->e_shoff = _w(new_e_shoff);
        ehdr->e_shnum = w2(2 + w2(ehdr->e_shnum));  /* {.rel,}__mcount_loc */
        ulseek(fd_map, 0, SEEK_SET);
        uwrite(fd_map, ehdr, sizeof(*ehdr));
}

static unsigned get_mcountsym(Elf_Sym const *const sym0,
                              Elf_Rel const *relp,
                              char const *const str0)
{
        unsigned mcountsym = 0;

        Elf_Sym const *const symp =
                &sym0[Elf_r_sym(relp)];
        char const *symname = &str0[w(symp->st_name)];
        char const *mcount = gpfx == '_' ? "_mcount" : "mcount";
        char const *fentry = "__fentry__";

        if (symname[0] == '.')
                ++symname;  /* ppc64 hack */
        if (strcmp(mcount, symname) == 0 ||
            (altmcount && strcmp(altmcount, symname) == 0) ||
            (strcmp(fentry, symname) == 0))
                mcountsym = Elf_r_sym(relp);

        return mcountsym;
}

static void get_sym_str_and_relp(Elf_Shdr const *const relhdr,
                                 Elf_Ehdr const *const ehdr,
                                 Elf_Sym const **sym0,
                                 char const **str0,
                                 Elf_Rel const **relp)
{
        Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
                + (void *)ehdr);
        unsigned const symsec_sh_link = w(relhdr->sh_link);
        Elf_Shdr const *const symsec = &shdr0[symsec_sh_link];
        Elf_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
        Elf_Rel const *const rel0 = (Elf_Rel const *)(_w(relhdr->sh_offset)
                + (void *)ehdr);

        *sym0 = (Elf_Sym const *)(_w(symsec->sh_offset)
                                  + (void *)ehdr);

        *str0 = (char const *)(_w(strsec->sh_offset)
                               + (void *)ehdr);

        *relp = rel0;
}

/*
 * Look at the relocations in order to find the calls to mcount.
 * Accumulate the section offsets that are found, and their relocation info,
 * onto the end of the existing arrays.
 */
static uint_t *sift_rel_mcount(uint_t *mlocp,
                               unsigned const offbase,
                               Elf_Rel **const mrelpp,
                               Elf_Shdr const *const relhdr,
                               Elf_Ehdr const *const ehdr,
                               unsigned const recsym,
                               uint_t const recval,
                               unsigned const reltype)
{
        uint_t *const mloc0 = mlocp;
        Elf_Rel *mrelp = *mrelpp;
        Elf_Sym const *sym0;
        char const *str0;
        Elf_Rel const *relp;
        unsigned rel_entsize = _w(relhdr->sh_entsize);
        unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
        unsigned mcountsym = 0;
        unsigned t;

        get_sym_str_and_relp(relhdr, ehdr, &sym0, &str0, &relp);

        for (t = nrel; t; --t) {
                if (!mcountsym)
                        mcountsym = get_mcountsym(sym0, relp, str0);

                if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) {
                        uint_t const addend =
                                _w(_w(relp->r_offset) - recval + mcount_adjust);
                        mrelp->r_offset = _w(offbase
                                + ((void *)mlocp - (void *)mloc0));
                        Elf_r_info(mrelp, recsym, reltype);
                        if (rel_entsize == sizeof(Elf_Rela)) {
                                ((Elf_Rela *)mrelp)->r_addend = addend;
                                *mlocp++ = 0;
                        } else
                                *mlocp++ = addend;

                        mrelp = (Elf_Rel *)(rel_entsize + (void *)mrelp);
                }
                relp = (Elf_Rel const *)(rel_entsize + (void *)relp);
        }
        *mrelpp = mrelp;
        return mlocp;
}

/*
 * Read the relocation table again, but this time its called on sections
 * that are not going to be traced. The mcount calls here will be converted
 * into nops.
 */
static void nop_mcount(Elf_Shdr const *const relhdr,
                       Elf_Ehdr const *const ehdr,
                       const char *const txtname)
{
        Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
                + (void *)ehdr);
        Elf_Sym const *sym0;
        char const *str0;
        Elf_Rel const *relp;
        Elf_Shdr const *const shdr = &shdr0[w(relhdr->sh_info)];
        unsigned rel_entsize = _w(relhdr->sh_entsize);
        unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
        unsigned mcountsym = 0;
        unsigned t;
        int once = 0;

        get_sym_str_and_relp(relhdr, ehdr, &sym0, &str0, &relp);

        for (t = nrel; t; --t) {
                int ret = -1;

                if (!mcountsym)
                        mcountsym = get_mcountsym(sym0, relp, str0);

                if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) {
                        if (make_nop)
                                ret = make_nop((void *)ehdr, shdr->sh_offset + relp->r_offset);
                        if (warn_on_notrace_sect && !once) {
                                printf("Section %s has mcount callers being ignored\n",
                                       txtname);
                                once = 1;
                                /* just warn? */
                                if (!make_nop)
                                        return;
                        }
                }

                /*
                 * If we successfully removed the mcount, mark the relocation
                 * as a nop (don't do anything with it).
                 */
                if (!ret) {
                        Elf_Rel rel;
                        rel = *(Elf_Rel *)relp;
                        Elf_r_info(&rel, Elf_r_sym(relp), rel_type_nop);
                        ulseek(fd_map, (void *)relp - (void *)ehdr, SEEK_SET);
                        uwrite(fd_map, &rel, sizeof(rel));
                }
                relp = (Elf_Rel const *)(rel_entsize + (void *)relp);
        }
}


/*
 * Find a symbol in the given section, to be used as the base for relocating
 * the table of offsets of calls to mcount.  A local or global symbol suffices,
 * but avoid a Weak symbol because it may be overridden; the change in value
 * would invalidate the relocations of the offsets of the calls to mcount.
 * Often the found symbol will be the unnamed local symbol generated by
 * GNU 'as' for the start of each section.  For example:
 *    Num:    Value  Size Type    Bind   Vis      Ndx Name
 *      2: 00000000     0 SECTION LOCAL  DEFAULT    1
 */
static unsigned find_secsym_ndx(unsigned const txtndx,
                                char const *const txtname,
                                uint_t *const recvalp,
                                Elf_Shdr const *const symhdr,
                                Elf_Ehdr const *const ehdr)
{
        Elf_Sym const *const sym0 = (Elf_Sym const *)(_w(symhdr->sh_offset)
                + (void *)ehdr);
        unsigned const nsym = _w(symhdr->sh_size) / _w(symhdr->sh_entsize);
        Elf_Sym const *symp;
        unsigned t;

        for (symp = sym0, t = nsym; t; --t, ++symp) {
                unsigned int const st_bind = ELF_ST_BIND(symp->st_info);

                if (txtndx == w2(symp->st_shndx)
                        /* avoid STB_WEAK */
                    && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
                        /* function symbols on ARM have quirks, avoid them */
                        if (w2(ehdr->e_machine) == EM_ARM
                            && ELF_ST_TYPE(symp->st_info) == STT_FUNC)
                                continue;

                        *recvalp = _w(symp->st_value);
                        return symp - sym0;
                }
        }
        fprintf(stderr, "Cannot find symbol for section %d: %s.\n",
                txtndx, txtname);
        fail_file();
}


/* Evade ISO C restriction: no declaration after statement in has_rel_mcount. */
static char const *
__has_rel_mcount(Elf_Shdr const *const relhdr,  /* is SHT_REL or SHT_RELA */
                 Elf_Shdr const *const shdr0,
                 char const *const shstrtab,
                 char const *const fname)
{
        /* .sh_info depends on .sh_type == SHT_REL[,A] */
        Elf_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
        char const *const txtname = &shstrtab[w(txthdr->sh_name)];

        if (strcmp("__mcount_loc", txtname) == 0) {
                fprintf(stderr, "warning: __mcount_loc already exists: %s\n",
                        fname);
                succeed_file();
        }
        if (w(txthdr->sh_type) != SHT_PROGBITS ||
            !(_w(txthdr->sh_flags) & SHF_EXECINSTR))
                return NULL;
        return txtname;
}

static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
                                  Elf_Shdr const *const shdr0,
                                  char const *const shstrtab,
                                  char const *const fname)
{
        if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
                return NULL;
        return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);
}


static unsigned tot_relsize(Elf_Shdr const *const shdr0,
                            unsigned nhdr,
                            const char *const shstrtab,
                            const char *const fname)
{
        unsigned totrelsz = 0;
        Elf_Shdr const *shdrp = shdr0;
        char const *txtname;

        for (; nhdr; --nhdr, ++shdrp) {
                txtname = has_rel_mcount(shdrp, shdr0, shstrtab, fname);
                if (txtname && is_mcounted_section_name(txtname))
                        totrelsz += _w(shdrp->sh_size);
        }
        return totrelsz;
}


/* Overall supervision for Elf32 ET_REL file. */
static void
do_func(Elf_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
{
        Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
                + (void *)ehdr);
        unsigned const nhdr = w2(ehdr->e_shnum);
        Elf_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
        char const *const shstrtab = (char const *)(_w(shstr->sh_offset)
                + (void *)ehdr);

        Elf_Shdr const *relhdr;
        unsigned k;

        /* Upper bound on space: assume all relevant relocs are for mcount. */
        unsigned const totrelsz = tot_relsize(shdr0, nhdr, shstrtab, fname);
        Elf_Rel *const mrel0 = umalloc(totrelsz);
        Elf_Rel *      mrelp = mrel0;

        /* 2*sizeof(address) <= sizeof(Elf_Rel) */
        uint_t *const mloc0 = umalloc(totrelsz>>1);
        uint_t *      mlocp = mloc0;

        unsigned rel_entsize = 0;
        unsigned symsec_sh_link = 0;

        for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
                char const *const txtname = has_rel_mcount(relhdr, shdr0,
                        shstrtab, fname);
                if (txtname && is_mcounted_section_name(txtname)) {
                        uint_t recval = 0;
                        unsigned const recsym = find_secsym_ndx(
                                w(relhdr->sh_info), txtname, &recval,
                                &shdr0[symsec_sh_link = w(relhdr->sh_link)],
                                ehdr);

                        rel_entsize = _w(relhdr->sh_entsize);
                        mlocp = sift_rel_mcount(mlocp,
                                (void *)mlocp - (void *)mloc0, &mrelp,
                                relhdr, ehdr, recsym, recval, reltype);
                } else if (txtname && (warn_on_notrace_sect || make_nop)) {
                        /*
                         * This section is ignored by ftrace, but still
                         * has mcount calls. Convert them to nops now.
                         */
                        nop_mcount(relhdr, ehdr, txtname);
                }
        }
        if (mloc0 != mlocp) {
                append_func(ehdr, shstr, mloc0, mlocp, mrel0, mrelp,
                            rel_entsize, symsec_sh_link);
        }
        free(mrel0);
        free(mloc0);
}
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