cosmopolitan/libc/dlopen/dlopen.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/atomic.h"
#include "libc/calls/calls.h"
#include "libc/calls/internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/calls/syscall_support-nt.internal.h"
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/dlopen/dlfcn.h"
#include "libc/elf/def.h"
#include "libc/elf/elf.h"
#include "libc/elf/struct/auxv.h"
#include "libc/elf/struct/ehdr.h"
#include "libc/elf/struct/phdr.h"
#include "libc/errno.h"
#include "libc/intrin/bits.h"
#include "libc/intrin/strace.internal.h"
#include "libc/limits.h"
#include "libc/nt/dll.h"
#include "libc/nt/enum/filemapflags.h"
#include "libc/nt/enum/pageflags.h"
#include "libc/nt/errors.h"
#include "libc/nt/memory.h"
#include "libc/nt/runtime.h"
#include "libc/runtime/internal.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/syslib.internal.h"
#include "libc/stdio/stdio.h"
#include "libc/stdio/sysparam.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/auxv.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/prot.h"
#include "libc/sysv/errfuns.h"
#include "libc/thread/thread.h"
#include "libc/thread/tls.h"

/**
 * @fileoverview Cosmopolitan Dynamic Linker.
 *
 * Every program built using Cosmopolitan is statically-linked. However
 * there are some cases, e.g. GUIs and video drivers, where linking the
 * host platform libraries is desirable. So what we do in such cases is
 * launch a stub executable using the host platform's libc, and longjmp
 * back into this executable. The stub executable passes back to us the
 * platform-specific dlopen() implementation, which we shall then wrap.
 *
 * @kudos jacereda for figuring out how to do this
 */

__static_yoink(".dlopen.x86_64.musl.elf");
__static_yoink(".dlopen.x86_64.glibc.elf");
__static_yoink(".dlopen.x86_64.freebsd.elf");
__static_yoink(".dlopen.aarch64.glibc.elf");

#define XNU_RTLD_LAZY   1
#define XNU_RTLD_NOW    2
#define XNU_RTLD_LOCAL  4
#define XNU_RTLD_GLOBAL 8

struct loaded {
  char *base;
  char *entry;
  Elf64_Ehdr eh;
  Elf64_Phdr ph[32];
};

static struct {
  atomic_uint once;
  bool is_supported;
  void *(*dlopen)(const char *, int);
  void *(*dlsym)(void *, const char *);
  int (*dlclose)(void *);
  char *(*dlerror)(void);
  jmp_buf jb;
} foreign;

static _Thread_local const char *last_dlerror;

static const unsigned align_mask = 4095;

static uintptr_t pgtrunc(uintptr_t x) {
  return x & ~align_mask;
}

static uintptr_t pground(uintptr_t x) {
  return pgtrunc(x + align_mask);
}

static unsigned pflags(unsigned x) {
  unsigned r = 0;
  if (x & PF_R) r += PROT_READ;
  if (x & PF_W) r += PROT_WRITE;
  if (x & PF_X) r += PROT_EXEC;
  return r;
}

static char *elf_map(int fd, Elf64_Ehdr *ehdr, Elf64_Phdr *phdr) {
  uintptr_t minva = -1;
  uintptr_t maxva = 0;
  for (Elf64_Phdr *p = phdr; p < &phdr[ehdr->e_phnum]; p++) {
    if (p->p_type != PT_LOAD) continue;
    if (p->p_vaddr < minva) minva = p->p_vaddr;
    if (p->p_vaddr + p->p_memsz > maxva) maxva = p->p_vaddr + p->p_memsz;
  }
  minva = pgtrunc(minva);
  maxva = pground(maxva);
  uint8_t *base = __sys_mmap(0, maxva - minva, PROT_NONE,
                             MAP_PRIVATE | MAP_ANONYMOUS, -1, 0, 0);
  if (base == MAP_FAILED) return MAP_FAILED;
  __sys_munmap(base, maxva - minva);
  for (Elf64_Phdr *p = phdr; p < &phdr[ehdr->e_phnum]; p++) {
    if (p->p_type != PT_LOAD) continue;
    uintptr_t off = p->p_vaddr & align_mask;
    uint8_t *start = base;
    start += pgtrunc(p->p_vaddr);
    size_t sz = pground(p->p_memsz + off);
    uint8_t *m = __sys_mmap(start, sz, PROT_WRITE,
                            MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0, 0);
    if (m == MAP_FAILED) return MAP_FAILED;
    ssize_t rr = pread(fd, m + off, p->p_filesz, p->p_offset);
    if (rr != (ssize_t)p->p_filesz) return MAP_FAILED;
    sys_mprotect(m, sz, pflags(p->p_flags));
  }
  return (void *)base;
}

static int elf_open(const char *file) {
  return open(file, O_RDONLY | O_CLOEXEC);
}

static bool elf_slurp(struct loaded *l, int fd, const char *file) {
  if (pread(fd, &l->eh, 64, 0) != 64) return false;
  if (!IsElf64Binary(&l->eh, 64)) return false;
  if (l->eh.e_phnum > ARRAYLEN(l->ph)) return false;
  int bytes = l->eh.e_phnum * sizeof(l->ph[0]);
  if (pread(fd, l->ph, bytes, l->eh.e_phoff) != bytes) return false;
  l->entry = (char *)l->eh.e_entry;
  return true;
}

static bool elf_load(struct loaded *l, const char *file) {
  int fd;
  if ((fd = elf_open(file)) == -1) return false;
  if (!elf_slurp(l, fd, file)) {
    close(fd);
    return false;
  }
  if ((l->base = elf_map(fd, &l->eh, l->ph)) == MAP_FAILED) {
    close(fd);
    return false;
  }
  l->entry += (uintptr_t)l->base;
  close(fd);
  return true;
}

static bool elf_interp(char *buf, size_t bsz, const char *file) {
  int fd;
  if ((fd = elf_open(file)) == -1) return false;
  struct loaded l;
  if (!elf_slurp(&l, fd, file)) {
    close(fd);
    return false;
  }
  for (unsigned i = 0; i < l.eh.e_phnum; i++) {
    if (l.ph[i].p_type == PT_INTERP) {
      if (l.ph[i].p_filesz >= bsz ||
          pread(fd, buf, l.ph[i].p_filesz, l.ph[i].p_offset) !=
              l.ph[i].p_filesz) {
        close(fd);
        return false;
      }
      break;
    }
  }
  close(fd);
  return true;
}

static long *push_strs(long *sp, char **list, int count) {
  *--sp = 0;
  while (count) *--sp = (long)list[--count];
  return sp;
}

static void elf_exec(const char *file, const char *iinterp, int argc,
                     char **argv, char **envp) {

  // get elf information
  struct loaded prog;
  if (!elf_load(&prog, file)) return;
  struct loaded interp;
  if (!elf_load(&interp, iinterp)) return;

  // count environment variables
  int envc = 0;
  while (envp[envc]) envc++;

  // create a stack for the new process just beneath our stack
  long *sp = (long *)__builtin_frame_address(0) - 256;

  // push auxiliary values
  *--sp = 0;
  Elf64_auxv_t *av;
  unsigned long key, val;
  for (av = (Elf64_auxv_t *)__auxv; (key = av->a_type); ++av) {
    val = av->a_un.a_val;
    if (key == AT_PHDR) val = (long)(prog.base + prog.eh.e_phoff);
    if (key == AT_PHENT) val = prog.eh.e_phentsize;
    if (key == AT_PHNUM) val = prog.eh.e_phnum;
    if (key == AT_PAGESZ) val = 0x1000;
    if (key == AT_BASE) val = (long)interp.base;
    if (key == AT_FLAGS) val = 0;
    if (key == AT_ENTRY) val = (long)prog.entry;
    if (key == AT_EXECFN) val = (long)argv[0];
    *--sp = val;
    *--sp = key;
  }

  // push main() arguments
  sp = push_strs(sp, envp, envc);
  sp = push_strs(sp, argv, argc);
  *--sp = argc;

#ifdef __x86_64__
  struct ps_strings {
    char **argv;
    int argc;
    char **envp;
    int envc;
  } pss = {argv, argc, envp, envc};
  asm volatile("mov\t%2,%%rsp\n\t"
               "jmpq\t*%1"
               : /* no outputs */
               : "D"(IsFreebsd() ? sp : 0), "S"(interp.entry), "d"(sp),
                 "b"(IsNetbsd() ? &pss : 0)
               : "memory");
  __builtin_unreachable();
#elif defined(__aarch64__)
  register long x0 asm("x0") = IsFreebsd() ? (long)sp : 0;
  register long x9 asm("x9") = (long)sp;
  register long x16 asm("x16") = (long)interp.entry;
  asm volatile("mov\tsp,x9\n\t"
               "br\tx16"
               : /* no outputs */
               : "r"(x0), "r"(x9), "r"(x16)
               : "memory");
  __builtin_unreachable();
#else
#error "unsupported architecture"
#endif
}

static wontreturn void foreign_helper(void **p) {
  foreign.dlopen = p[0];
  foreign.dlsym = p[1];
  foreign.dlclose = p[2];
  foreign.dlerror = p[3];
  longjmp(foreign.jb, 1);
}

static void foreign_setup(void) {
  char interp[256] = {0};
  if (!elf_interp(interp, sizeof(interp), "/usr/bin/env")) return;
  const char *dlopen_helper = 0;
#ifdef __x86_64__
  if (IsFreebsd()) {
    dlopen_helper = "/zip/.dlopen.x86_64.freebsd.elf";
  } else if (IsLinux()) {
    if (fileexists("/lib64/ld-linux-x86-64.so.2")) {
      dlopen_helper = "/zip/.dlopen.x86_64.glibc.elf";
    } else {
      dlopen_helper = "/zip/.dlopen.x86_64.musl.elf";
    }
  }
#elif defined(__aarch64__)
  if (IsLinux()) {
    dlopen_helper = "/zip/.dlopen.aarch64.glibc.elf";
  }
#endif
  if (!dlopen_helper) {
    return;  // this platform isn't supported yet
  }
  if (!setjmp(foreign.jb)) {
    elf_exec(dlopen_helper, interp, 2,
             (char *[]){
                 program_invocation_name,
                 (char *)foreign_helper,
                 NULL,
             },
             environ);
    return;  // if it returns then it failed
  }
  foreign.is_supported = true;
}

static bool foreign_init(void) {
  bool res;
  cosmo_once(&foreign.once, foreign_setup);
  if (!(res = foreign.is_supported)) {
    last_dlerror = "dlopen() isn't supported on this platform";
  }
  return res;
}

static int dlclose_nt(void *handle) {
  int res;
  if (FreeLibrary((uintptr_t)handle)) {
    res = 0;
  } else {
    last_dlerror = "FreeLibrary() failed";
    res = -1;
  }
  return res;
}

static void *dlopen_nt(const char *path, int mode) {
  int n;
  uintptr_t handle;
  char16_t path16[PATH_MAX + 2];
  if (mode & ~(RTLD_LOCAL | RTLD_LAZY | RTLD_NOW)) {
    last_dlerror = "invalid mode";
    return 0;
  }
  if ((n = __mkntpath(path, path16)) == -1) {
    last_dlerror = "path invalid";
    return 0;
  }
  if (n > 3 &&                 //
      path16[n - 3] == '.' &&  //
      path16[n - 2] == 's' &&  //
      path16[n - 1] == 'o') {
    path16[n - 2] = 'd';
    path16[n - 1] = 'l';
    path16[n + 0] = 'l';
    path16[n + 1] = 0;
  }
  if (!(handle = LoadLibrary(path16))) {
    last_dlerror = "library not found";
  }
  return (void *)handle;
}

static char *dlsym_nt_alloc_rwx_block(void) {
  uintptr_t h;
  char *p = 0;
  if ((h = CreateFileMapping(-1, 0, kNtPageExecuteReadwrite, 0, 65536, 0)) &&
      (p = MapViewOfFileEx(h, kNtFileMapWrite | kNtFileMapExecute, 0, 0, 65536,
                           0))) {
    WRITE32LE(p, 4);  // store used index
  } else {
    last_dlerror = "out of memory";
  }
  return p;
}

static void *dlsym_nt_alloc_rwx(size_t n) {
  void *res;
  static char *block;
  static pthread_spinlock_t lock;
  pthread_spin_lock(&lock);
  if (!block || READ32LE(block) + n > 65536) {
    if (!(block = dlsym_nt_alloc_rwx_block())) {
      pthread_spin_unlock(&lock);
      return 0;
    }
  }
  res = block + READ32LE(block);
  WRITE32LE(block, READ32LE(block) + n);
  pthread_spin_unlock(&lock);
  return res;
}

static void *dlsym_nt_thunk(void *func, void *tramp) {
  unsigned char *code;
  if (!(code = dlsym_nt_alloc_rwx(27))) return 0;
  // push %rbp
  code[0] = 0x55;
  // mov %rsp,%rbp
  code[1] = 0x48;
  code[2] = 0x89;
  code[3] = 0xe5;
  // movabs $func,%rax
  code[4] = 0x48;
  code[5] = 0xb8;
  WRITE64LE(code + 6, (uintptr_t)func);
  // movabs $tramp,%r10
  code[14] = 0x49;
  code[15] = 0xba;
  WRITE64LE(code + 16, (uintptr_t)tramp);
  // jmp *%r10
  code[24] = 0x41;
  code[25] = 0xff;
  code[26] = 0xe2;
  return code;
}

static void *dlsym_nt(void *handle, const char *name) {
  long __sysv2nt14();
  void *x64_abi_func;
  void *sysv_abi_func = 0;
  if ((x64_abi_func = GetProcAddress((uintptr_t)handle, name))) {
    sysv_abi_func = dlsym_nt_thunk(x64_abi_func, __sysv2nt14);
  } else {
    last_dlerror = "symbol not found";
  }
  return sysv_abi_func;
}

static void *dlopen_silicon(const char *path, int mode) {
  int n;
  int xnu_mode = 0;
  char path2[PATH_MAX + 5];
  if (mode & ~(RTLD_LOCAL | RTLD_LAZY | RTLD_NOW | RTLD_GLOBAL)) {
    xnu_mode = -1;  // punt error to system dlerror() impl
  }
  if (!(mode & RTLD_GLOBAL)) {
    xnu_mode |= XNU_RTLD_LOCAL;  // unlike Linux, XNU defaults to RTLD_GLOBAL
  }
  if (mode & RTLD_NOW) {
    xnu_mode |= XNU_RTLD_NOW;
  }
  if (mode & RTLD_LAZY) {
    xnu_mode |= XNU_RTLD_LAZY;
  }
  if ((n = strlen(path)) < PATH_MAX && n > 3 &&  //
      path[n - 3] == '.' &&                      //
      path[n - 2] == 's' &&                      //
      path[n - 1] == 'o') {
    memcpy(path2, path, n);
    path2[n - 2] = 'd';
    path2[n - 1] = 'y';
    path2[n + 0] = 'l';
    path2[n + 1] = 'i';
    path2[n + 2] = 'b';
    path2[n + 3] = 0;
    path = path2;
  }
  return __syslib->__dlopen(path, xnu_mode);
}

/**
 * Opens dynamic shared object using host platform libc.
 *
 * If a `path` ending with `.so` is passed on Windows or MacOS, then
 * this wrapper will automatically change it to `.dll` or `.dylib` to
 * increase its chance of successfully loading.
 *
 * @param mode is a bitmask that can contain:
 *     - `RTLD_LOCAL` (default)
 *     - `RTLD_GLOBAL` (not supported on Windows)
 *     - `RTLD_LAZY`
 *     - `RTLD_NOW`
 * @return dso handle, or NULL w/ dlerror()
 */
void *dlopen(const char *path, int mode) {
  void *res;
  if (IsWindows()) {
    res = dlopen_nt(path, mode);
  } else if (IsXnuSilicon()) {
    res = dlopen_silicon(path, mode);
  } else if (IsXnu()) {
    last_dlerror = "dlopen() isn't supported on x86-64 MacOS";
    res = 0;
  } else if (foreign_init()) {
    res = foreign.dlopen(path, mode);
  } else {
    res = 0;
  }
  STRACE("dlopen(%#s, %d) → %p", path, mode, res);
  return res;
}

/**
 * Obtains address of symbol from dynamic shared object.
 *
 * On Windows you can only use this to lookup function addresses.
 * Returned functions are trampolined to conform to System V ABI.
 *
 * @param handle was opened by dlopen()
 * @return address of symbol, or NULL w/ dlerror()
 */
void *dlsym(void *handle, const char *name) {
  void *res;
  if (IsWindows()) {
    res = dlsym_nt(handle, name);
  } else if (IsXnuSilicon()) {
    res = __syslib->__dlsym(handle, name);
  } else if (IsXnu()) {
    last_dlerror = "dlopen() isn't supported on x86-64 MacOS";
    res = 0;
  } else if (foreign_init()) {
    res = foreign.dlsym(handle, name);
  } else {
    res = 0;
  }
  STRACE("dlsym(%p, %#s) → %p", handle, name, res);
  return res;
}

/**
 * Closes dynamic shared object.
 *
 * @param handle was opened by dlopen()
 * @return 0 on success, or -1 w/ dlerror()
 */
int dlclose(void *handle) {
  int res;
  if (IsWindows()) {
    res = dlclose_nt(handle);
  } else if (IsXnuSilicon()) {
    res = __syslib->__dlclose(handle);
  } else if (IsXnu()) {
    last_dlerror = "dlopen() isn't supported on x86-64 MacOS";
    res = -1;
  } else if (foreign_init()) {
    res = foreign.dlclose(handle);
  } else {
    res = -1;
  }
  STRACE("dlclose(%p) → %d", handle, res);
  return res;
}

/**
 * Returns string describing last dlopen/dlsym/dlclose error.
 */
char *dlerror(void) {
  char *res;
  if (IsXnuSilicon()) {
    res = __syslib->__dlerror();
  } else if (IsWindows() || IsXnu()) {
    res = (char *)last_dlerror;
  } else if (foreign_init()) {
    res = foreign.dlerror();
  } else {
    res = (char *)last_dlerror;
  }
  STRACE("dlerror() → %#s", res);
  return res;
}

#ifdef __x86_64__
static textstartup void dlopen_init() {
  if (IsLinux() || IsFreebsd() || IsNetbsd()) {
    // switch from %fs to %gs for tls
    struct CosmoTib *tib = __get_tls();
    __morph_tls();
    __set_tls(tib);
  }
}
const void *const dlopen_ctor[] initarray = {
    dlopen_init,
};
#endif