/*
 * Copyright 2015 Mentor Graphics Corporation.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; version 2 of the
 * License.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * vdsomunge - Host program which produces a shared object
 * architecturally specified to be usable by both soft- and hard-float
 * programs.
 *
 * The Procedure Call Standard for the ARM Architecture (ARM IHI
 * 0042E) says:
 *
 *      6.4.1 VFP and Base Standard Compatibility
 *
 *      Code compiled for the VFP calling standard is compatible with
 *      the base standard (and vice-versa) if no floating-point or
 *      containerized vector arguments or results are used.
 *
 * And ELF for the ARM Architecture (ARM IHI 0044E) (Table 4-2) says:
 *
 *      If both EF_ARM_ABI_FLOAT_XXXX bits are clear, conformance to the
 *      base procedure-call standard is implied.
 *
 * The VDSO is built with -msoft-float, as with the rest of the ARM
 * kernel, and uses no floating point arguments or results.  The build
 * process will produce a shared object that may or may not have the
 * EF_ARM_ABI_FLOAT_SOFT flag set (it seems to depend on the binutils
 * version; binutils starting with 2.24 appears to set it).  The
 * EF_ARM_ABI_FLOAT_HARD flag should definitely not be set, and this
 * program will error out if it is.
 *
 * If the soft-float flag is set, this program clears it.  That's all
 * it does.
 */

#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#define swab16(x) \
        ((((x) & 0x00ff) << 8) | \
         (((x) & 0xff00) >> 8))

#define swab32(x) \
        ((((x) & 0x000000ff) << 24) | \
         (((x) & 0x0000ff00) <<  8) | \
         (((x) & 0x00ff0000) >>  8) | \
         (((x) & 0xff000000) >> 24))

#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
#define HOST_ORDER ELFDATA2LSB
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define HOST_ORDER ELFDATA2MSB
#endif

/* Some of the ELF constants we'd like to use were added to <elf.h>
 * relatively recently.
 */
#ifndef EF_ARM_EABI_VER5
#define EF_ARM_EABI_VER5 0x05000000
#endif

#ifndef EF_ARM_ABI_FLOAT_SOFT
#define EF_ARM_ABI_FLOAT_SOFT 0x200
#endif

#ifndef EF_ARM_ABI_FLOAT_HARD
#define EF_ARM_ABI_FLOAT_HARD 0x400
#endif

static int failed;
static const char *argv0;
static const char *outfile;

static void fail(const char *fmt, ...)
{
        va_list ap;

        failed = 1;
        fprintf(stderr, "%s: ", argv0);
        va_start(ap, fmt);
        vfprintf(stderr, fmt, ap);
        va_end(ap);
        exit(EXIT_FAILURE);
}

static void cleanup(void)
{
        if (failed && outfile != NULL)
                unlink(outfile);
}

static Elf32_Word read_elf_word(Elf32_Word word, bool swap)
{
        return swap ? swab32(word) : word;
}

static Elf32_Half read_elf_half(Elf32_Half half, bool swap)
{
        return swap ? swab16(half) : half;
}

static void write_elf_word(Elf32_Word val, Elf32_Word *dst, bool swap)
{
        *dst = swap ? swab32(val) : val;
}

int main(int argc, char **argv)
{
        const Elf32_Ehdr *inhdr;
        bool clear_soft_float;
        const char *infile;
        Elf32_Word e_flags;
        const void *inbuf;
        struct stat stat;
        void *outbuf;
        bool swap;
        int outfd;
        int infd;

        atexit(cleanup);
        argv0 = argv[0];

        if (argc != 3)
                fail("Usage: %s [infile] [outfile]\n", argv[0]);

        infile = argv[1];
        outfile = argv[2];

        infd = open(infile, O_RDONLY);
        if (infd < 0)
                fail("Cannot open %s: %s\n", infile, strerror(errno));

        if (fstat(infd, &stat) != 0)
                fail("Failed stat for %s: %s\n", infile, strerror(errno));

        inbuf = mmap(NULL, stat.st_size, PROT_READ, MAP_PRIVATE, infd, 0);
        if (inbuf == MAP_FAILED)
                fail("Failed to map %s: %s\n", infile, strerror(errno));

        close(infd);

        inhdr = inbuf;

        if (memcmp(&inhdr->e_ident, ELFMAG, SELFMAG) != 0)
                fail("Not an ELF file\n");

        if (inhdr->e_ident[EI_CLASS] != ELFCLASS32)
                fail("Unsupported ELF class\n");

        swap = inhdr->e_ident[EI_DATA] != HOST_ORDER;

        if (read_elf_half(inhdr->e_type, swap) != ET_DYN)
                fail("Not a shared object\n");

        if (read_elf_half(inhdr->e_machine, swap) != EM_ARM)
                fail("Unsupported architecture %#x\n", inhdr->e_machine);

        e_flags = read_elf_word(inhdr->e_flags, swap);

        if (EF_ARM_EABI_VERSION(e_flags) != EF_ARM_EABI_VER5) {
                fail("Unsupported EABI version %#x\n",
                     EF_ARM_EABI_VERSION(e_flags));
        }

        if (e_flags & EF_ARM_ABI_FLOAT_HARD)
                fail("Unexpected hard-float flag set in e_flags\n");

        clear_soft_float = !!(e_flags & EF_ARM_ABI_FLOAT_SOFT);

        outfd = open(outfile, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
        if (outfd < 0)
                fail("Cannot open %s: %s\n", outfile, strerror(errno));

        if (ftruncate(outfd, stat.st_size) != 0)
                fail("Cannot truncate %s: %s\n", outfile, strerror(errno));

        outbuf = mmap(NULL, stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED,
                      outfd, 0);
        if (outbuf == MAP_FAILED)
                fail("Failed to map %s: %s\n", outfile, strerror(errno));

        close(outfd);

        memcpy(outbuf, inbuf, stat.st_size);

        if (clear_soft_float) {
                Elf32_Ehdr *outhdr;

                outhdr = outbuf;
                e_flags &= ~EF_ARM_ABI_FLOAT_SOFT;
                write_elf_word(e_flags, &outhdr->e_flags, swap);
        }

        if (msync(outbuf, stat.st_size, MS_SYNC) != 0)
                fail("Failed to sync %s: %s\n", outfile, strerror(errno));

        return EXIT_SUCCESS;
}