Add dynamic/static checking to file (printing dynamic linker if found).

toys/pending/file.c

@@ -3,6 +3,8 @@
  * Copyright 2016 The Android Open Source Project
  *
  * See http:https://pubs.opengroup.org/onlinepubs/9699919799/utilities/file.html
+ *
+ * TODO: ar
 
 USE_FILE(NEWTOY(file, "<1", TOYFLAG_USR|TOYFLAG_BIN))
 
@@ -22,9 +24,11 @@ GLOBALS(
  int max_name_len;
 )
 
-static void do_elf_file()
+// We don't trust elf.h to be there, and two codepaths for 32/64 is awkward
+// anyway, so calculate struct offsets manually. (It's a fixed ABI.)
+static void do_elf_file(int fd)
 {
- int elf_endian = toybuf[5], e_type, e_machine, i;
+ int endian = toybuf[5], bits = toybuf[4], i, j;
  int64_t (*elf_int)(void *ptr, unsigned size) = peek_le;
  // Values from include/linux/elf-em.h (plus arch/*/include/asm/elf.h)
  // Names are linux/arch/ directory name
@@ -40,51 +44,81 @@ static void do_elf_file()
  xprintf("ELF ");
 
  // "64-bit"
- if (toybuf[4] == 1) xprintf("32-bit ");
- else if (toybuf[4] == 2) xprintf("64-bit ");
- else xprintf("(bad class %d)", toybuf[4]);
+ if (bits == 1) xprintf("32-bit ");
+ else if (bits == 2) xprintf("64-bit ");
+ else {
+ xprintf("(bad class %d) ", bits);
+ bits = 0;
+ }
+
+ // e_machine, ala "x86", from big table above
+ j = elf_int(toybuf+18, 2);
+ for (i = 0; i<ARRAY_LEN(type); i++) if (j==type[i].val) break;
+ if (i<ARRAY_LEN(type)) xprintf("%s ", type[i].name);
+ else xprintf("(unknown arch %d) ", j);
 
  // "LSB"
- if (elf_endian == 1) xprintf("LSB ");
- else if (elf_endian == 2) {
+ if (endian == 1) xprintf("LSB ");
+ else if (endian == 2) {
  xprintf("MSB ");
  elf_int = peek_be;
  } else {
- xprintf("(bad endian %d)\n", elf_endian);
-
- // At this point we can't parse remaining fields.
- return;
+ xprintf("(bad endian %d)\n", endian);
+ endian = 0;
  }
 
  // ", executable"
- e_type = elf_int(&toybuf[0x10], 2);
- if (e_type == 1) xprintf("relocatable");
- else if (e_type == 2) xprintf("executable");
- else if (e_type == 3) xprintf("shared object");
- else if (e_type == 4) xprintf("core dump");
- else xprintf("(invalid type %d)", e_type);
-
- // ", x86-64"
- e_machine = elf_int(&toybuf[0x12], 2);
- for (i = 0; i<ARRAY_LEN(type); i++) if (e_machine == type[i].val) break;
- if (i<ARRAY_LEN(type)) xprintf(", %s", type[i].name);
- else xprintf(", (unknown arch %d)", e_machine);
-
- // "version 1"
- xprintf(", version %d", toybuf[6]);
-
- // " (SYSV)"
- // TODO: will we ever meet any of the others in practice?
- if (!toybuf[7]) xprintf(" (SYSV)");
- else xprintf(" (OS %d)", toybuf[7]);
+ i = elf_int(toybuf+16, 2);
+ if (i == 1) xprintf("relocatable");
+ else if (i == 2) xprintf("executable");
+ else if (i == 3) xprintf("shared object");
+ else if (i == 4) xprintf("core dump");
+ else xprintf("(bad type %d)", i);
+
+ bits--;
+ // If we know our bits and endianness and phentsize agrees show dynamic linker
+ if ((bits&1)==bits && endian &&
+ (i = elf_int(toybuf+42+12*bits, 2)) == 32+24*bits)
+ {
+ char *map, *phdr;
+ int phsize = i, phnum = elf_int(toybuf+44+12*bits, 2),
+ psz = sysconf(_SC_PAGE_SIZE), lib = 0;
+ off_t phoff = elf_int(toybuf+28+4*bits, 4+4*bits),
+ mapoff = phoff^(phoff&(psz-1));
+
+ // map e_phentsize*e_phnum bytes at e_phoff
+ map = mmap(0, phsize*phnum, PROT_READ, MAP_SHARED, fd, mapoff);
+ if (map) {
+ // Find PT_INTERP entry. (Not: fields got reordered for 64 bit)
+ for (i = 0; i<phnum; i++) {
+ long long dlpos, dllen;
+
+ // skip non-PT_INTERP entries
+ j = elf_int(phdr = map+(phoff-mapoff)+i*phsize, 4);
+ if (j==2) lib++;
+ if (j!=3) continue;
+
+ // Read p_offset and p_filesz
+ j = bits+1;
+ dlpos = elf_int(phdr+4*j, 4*j);
+ dllen = elf_int(phdr+16*j, 4*j);
+ if (dllen<0 || dllen>sizeof(toybuf)-128
+ || dlpos!=lseek(fd, dlpos, SEEK_SET)
+ || dllen!=readall(fd, toybuf+128, dllen)) break;
+ printf(", dynamic (%.*s)", (int)dllen, toybuf+128);
+ }
+ if (!lib) printf(", static");
+ else printf(", needs %d lib%s", lib, lib>1 ? "s" : "");
+ munmap(map, phsize*phnum);
+ }
+ }
 
  // TODO: we'd need to actually parse the ELF file to report the rest...
  // ", dynamically linked"
  // " (uses shared libs)"
  // ", for Linux 2.6.24"
  // ", BuildID[sha1]=SHA"
  // ", stripped"
-
  xputc('\n');
 }
 
@@ -95,9 +129,8 @@ static void do_regular_file(int fd, char *name)
 
  if (len<0) perror_msg("%s", name);
 
- if (len>20 && strstart(&s, "\177ELF")) {
- do_elf_file(len);
- } else if (len>28 && strstart(&s, "\x89PNG\x0d\x0a\x1a\x0a")) {
+ if (len>40 && strstart(&s, "\177ELF")) do_elf_file(fd);
+ else if (len>28 && strstart(&s, "\x89PNG\x0d\x0a\x1a\x0a")) {
  // PNG is big-endian: https://www.w3.org/TR/PNG/#7Integers-and-byte-order
  int chunk_length = peek_be(s, 4);