/*
 * vdso2c - A vdso image preparation tool
 * Copyright (c) 2014 Andy Lutomirski and others
 * Licensed under the GPL v2
 *
 * vdso2c requires stripped and unstripped input.  It would be trivial
 * to fully strip the input in here, but, for reasons described below,
 * we need to write a section table.  Doing this is more or less
 * equivalent to dropping all non-allocatable sections, but it's
 * easier to let objcopy handle that instead of doing it ourselves.
 * If we ever need to do something fancier than what objcopy provides,
 * it would be straightforward to add here.
 *
 * We're keep a section table for a few reasons:
 *
 * The Go runtime had a couple of bugs: it would read the section
 * table to try to figure out how many dynamic symbols there were (it
 * shouldn't have looked at the section table at all) and, if there
 * were no SHT_SYNDYM section table entry, it would use an
 * uninitialized value for the number of symbols.  An empty DYNSYM
 * table would work, but I see no reason not to write a valid one (and
 * keep full performance for old Go programs).  This hack is only
 * needed on x86_64.
 *
 * The bug was introduced on 2012-08-31 by:
 * https://code.google.com/p/go/source/detail?r=56ea40aac72b
 * and was fixed on 2014-06-13 by:
 * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
 *
 * Binutils has issues debugging the vDSO: it reads the section table to
 * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
 * would break build-id if we removed the section table.  Binutils
 * also requires that shstrndx != 0.  See:
 * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
 *
 * elfutils might not look for PT_NOTE if there is a section table at
 * all.  I don't know whether this matters for any practical purpose.
 *
 * For simplicity, rather than hacking up a partial section table, we
 * just write a mostly complete one.  We omit non-dynamic symbols,
 * though, since they're rather large.
 *
 * Once binutils gets fixed, we might be able to drop this for all but
 * the 64-bit vdso, since build-id only works in kernel RPMs, and
 * systems that update to new enough kernel RPMs will likely update
 * binutils in sync.  build-id has never worked for home-built kernel
 * RPMs without manual symlinking, and I suspect that no one ever does
 * that.
 */

#include <inttypes.h>
#include <stdint.h>
#include <unistd.h>
#include <stdarg.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <err.h>

#include <sys/mman.h>
#include <sys/types.h>

#include <tools/le_byteshift.h>

#include <linux/elf.h>
#include <linux/types.h>

const char *outfilename;

/* Symbols that we need in vdso2c. */
enum {
        sym_vvar_start,
        sym_vvar_page,
        sym_hpet_page,
        sym_pvclock_page,
        sym_VDSO_FAKE_SECTION_TABLE_START,
        sym_VDSO_FAKE_SECTION_TABLE_END,
};

const int special_pages[] = {
        sym_vvar_page,
        sym_hpet_page,
        sym_pvclock_page,
};

struct vdso_sym {
        const char *name;
        bool export;
};

struct vdso_sym required_syms[] = {
        [sym_vvar_start] = {"vvar_start", true},
        [sym_vvar_page] = {"vvar_page", true},
        [sym_hpet_page] = {"hpet_page", true},
        [sym_pvclock_page] = {"pvclock_page", true},
        [sym_VDSO_FAKE_SECTION_TABLE_START] = {
                "VDSO_FAKE_SECTION_TABLE_START", false
        },
        [sym_VDSO_FAKE_SECTION_TABLE_END] = {
                "VDSO_FAKE_SECTION_TABLE_END", false
        },
        {"VDSO32_NOTE_MASK", true},
        {"__kernel_vsyscall", true},
        {"__kernel_sigreturn", true},
        {"__kernel_rt_sigreturn", true},
        {"int80_landing_pad", true},
};

__attribute__((format(printf, 1, 2))) __attribute__((noreturn))
static void fail(const char *format, ...)
{
        va_list ap;
        va_start(ap, format);
        fprintf(stderr, "Error: ");
        vfprintf(stderr, format, ap);
        if (outfilename)
                unlink(outfilename);
        exit(1);
        va_end(ap);
}

/*
 * Evil macros for little-endian reads and writes
 */
#define GLE(x, bits, ifnot)                                             \
        __builtin_choose_expr(                                          \
                (sizeof(*(x)) == bits/8),                               \
                (__typeof__(*(x)))get_unaligned_le##bits(x), ifnot)

extern void bad_get_le(void);
#define LAST_GLE(x)                                                     \
        __builtin_choose_expr(sizeof(*(x)) == 1, *(x), bad_get_le())

#define GET_LE(x)                                                       \
        GLE(x, 64, GLE(x, 32, GLE(x, 16, LAST_GLE(x))))

#define PLE(x, val, bits, ifnot)                                        \
        __builtin_choose_expr(                                          \
                (sizeof(*(x)) == bits/8),                               \
                put_unaligned_le##bits((val), (x)), ifnot)

extern void bad_put_le(void);
#define LAST_PLE(x, val)                                                \
        __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), bad_put_le())

#define PUT_LE(x, val)                                  \
        PLE(x, val, 64, PLE(x, val, 32, PLE(x, val, 16, LAST_PLE(x, val))))


#define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))

#define BITSFUNC3(name, bits, suffix) name##bits##suffix
#define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
#define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )

#define INT_BITS BITSFUNC2(int, ELF_BITS, _t)

#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)

#define ELF_BITS 64
#include "vdso2c.h"
#undef ELF_BITS

#define ELF_BITS 32
#include "vdso2c.h"
#undef ELF_BITS

static void go(void *raw_addr, size_t raw_len,
               void *stripped_addr, size_t stripped_len,
               FILE *outfile, const char *name)
{
        Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;

        if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
                go64(raw_addr, raw_len, stripped_addr, stripped_len,
                     outfile, name);
        } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
                go32(raw_addr, raw_len, stripped_addr, stripped_len,
                     outfile, name);
        } else {
                fail("unknown ELF class\n");
        }
}

static void map_input(const char *name, void **addr, size_t *len, int prot)
{
        off_t tmp_len;

        int fd = open(name, O_RDONLY);
        if (fd == -1)
                err(1, "%s", name);

        tmp_len = lseek(fd, 0, SEEK_END);
        if (tmp_len == (off_t)-1)
                err(1, "lseek");
        *len = (size_t)tmp_len;

        *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
        if (*addr == MAP_FAILED)
                err(1, "mmap");

        close(fd);
}

int main(int argc, char **argv)
{
        size_t raw_len, stripped_len;
        void *raw_addr, *stripped_addr;
        FILE *outfile;
        char *name, *tmp;
        int namelen;

        if (argc != 4) {
                printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
                return 1;
        }

        /*
         * Figure out the struct name.  If we're writing to a .so file,
         * generate raw output insted.
         */
        name = strdup(argv[3]);
        namelen = strlen(name);
        if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
                name = NULL;
        } else {
                tmp = strrchr(name, '/');
                if (tmp)
                        name = tmp + 1;
                tmp = strchr(name, '.');
                if (tmp)
                        *tmp = '\0';
                for (tmp = name; *tmp; tmp++)
                        if (*tmp == '-')
                                *tmp = '_';
        }

        map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
        map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);

        outfilename = argv[3];
        outfile = fopen(outfilename, "w");
        if (!outfile)
                err(1, "%s", argv[2]);

        go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);

        munmap(raw_addr, raw_len);
        munmap(stripped_addr, stripped_len);
        fclose(outfile);

        return 0;
}