ash: less hackish implementation of evaltreenr()
[oweals/busybox.git] / archival / tar.c
index 25042589c2d90afddcd5c01ff8f3d3cb54b420d0..280ded4e14e325811e2cf976a050bac6e7ba4b27 100644 (file)
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
 
-/* TODO: security with -C DESTDIR option can be enhanced.
- * Consider tar file created via:
- * $ tar cvf bug.tar anything.txt
- * $ ln -s /tmp symlink
- * $ tar --append -f bug.tar symlink
- * $ rm symlink
- * $ mkdir symlink
- * $ tar --append -f bug.tar symlink/evil.py
- *
- * This will result in an archive which contains:
- * $ tar --list -f bug.tar
- * anything.txt
- * symlink
- * symlink/evil.py
- *
- * Untarring it puts evil.py in '/tmp' even if the -C DESTDIR is given.
- * This doesn't feel right, and IIRC GNU tar doesn't do that.
- */
+//config:config TAR
+//config:      bool "tar (40 kb)"
+//config:      default y
+//config:      help
+//config:      tar is an archiving program. It's commonly used with gzip to
+//config:      create compressed archives. It's probably the most widely used
+//config:      UNIX archive program.
+//config:
+//config:config FEATURE_TAR_LONG_OPTIONS
+//config:      bool "Enable long options"
+//config:      default y
+//config:      depends on TAR && LONG_OPTS
+//config:
+//config:config FEATURE_TAR_CREATE
+//config:      bool "Enable -c (archive creation)"
+//config:      default y
+//config:      depends on TAR
+//config:
+//config:config FEATURE_TAR_AUTODETECT
+//config:      bool "Autodetect compressed tarballs"
+//config:      default y
+//config:      depends on TAR && (FEATURE_SEAMLESS_Z || FEATURE_SEAMLESS_GZ || FEATURE_SEAMLESS_BZ2 || FEATURE_SEAMLESS_LZMA || FEATURE_SEAMLESS_XZ)
+//config:      help
+//config:      With this option tar can automatically detect compressed
+//config:      tarballs. Currently it works only on files (not pipes etc).
+//config:
+//config:config FEATURE_TAR_FROM
+//config:      bool "Enable -X (exclude from) and -T (include from) options)"
+//config:      default y
+//config:      depends on TAR
+//config:      help
+//config:      If you enable this option you'll be able to specify
+//config:      a list of files to include or exclude from an archive.
+//config:
+//config:config FEATURE_TAR_OLDGNU_COMPATIBILITY
+//config:      bool "Support old tar header format"
+//config:      default y
+//config:      depends on TAR || DPKG
+//config:      help
+//config:      This option is required to unpack archives created in
+//config:      the old GNU format; help to kill this old format by
+//config:      repacking your ancient archives with the new format.
+//config:
+//config:config FEATURE_TAR_OLDSUN_COMPATIBILITY
+//config:      bool "Enable untarring of tarballs with checksums produced by buggy Sun tar"
+//config:      default y
+//config:      depends on TAR || DPKG
+//config:      help
+//config:      This option is required to unpack archives created by some old
+//config:      version of Sun's tar (it was calculating checksum using signed
+//config:      arithmetic). It is said to be fixed in newer Sun tar, but "old"
+//config:      tarballs still exist.
+//config:
+//config:config FEATURE_TAR_GNU_EXTENSIONS
+//config:      bool "Support GNU tar extensions (long filenames)"
+//config:      default y
+//config:      depends on TAR || DPKG
+//config:
+//config:config FEATURE_TAR_TO_COMMAND
+//config:      bool "Support writing to an external program (--to-command)"
+//config:      default y
+//config:      depends on TAR && FEATURE_TAR_LONG_OPTIONS
+//config:      help
+//config:      If you enable this option you'll be able to instruct tar to send
+//config:      the contents of each extracted file to the standard input of an
+//config:      external program.
+//config:
+//config:config FEATURE_TAR_UNAME_GNAME
+//config:      bool "Enable use of user and group names"
+//config:      default y
+//config:      depends on TAR
+//config:      help
+//config:      Enable use of user and group names in tar. This affects contents
+//config:      listings (-t) and preserving permissions when unpacking (-p).
+//config:      +200 bytes.
+//config:
+//config:config FEATURE_TAR_NOPRESERVE_TIME
+//config:      bool "Enable -m (do not preserve time) GNU option"
+//config:      default y
+//config:      depends on TAR
+//config:
+//config:config FEATURE_TAR_SELINUX
+//config:      bool "Support extracting SELinux labels"
+//config:      default n
+//config:      depends on TAR && SELINUX
+//config:      help
+//config:      With this option busybox supports restoring SELinux labels
+//config:      when extracting files from tar archives.
 
 //applet:IF_TAR(APPLET(tar, BB_DIR_BIN, BB_SUID_DROP))
 //kbuild:lib-$(CONFIG_TAR) += tar.o
 
 #include <fnmatch.h>
 #include "libbb.h"
+#include "common_bufsiz.h"
 #include "bb_archive.h"
 /* FIXME: Stop using this non-standard feature */
 #ifndef FNM_LEADING_DIR
 # define FNM_LEADING_DIR 0
 #endif
 
-
-//#define DBG(fmt, ...) bb_error_msg("%s: " fmt, __func__, ## __VA_ARGS__)
-#define DBG(...) ((void)0)
+#if 0
+# define DBG(fmt, ...) bb_error_msg("%s: " fmt, __func__, ## __VA_ARGS__)
+#else
+# define DBG(...) ((void)0)
+#endif
+#define DBG_OPTION_PARSING 0
 
 
 #define block_buf bb_common_bufsiz1
-
-
-#if !ENABLE_FEATURE_SEAMLESS_GZ && !ENABLE_FEATURE_SEAMLESS_BZ2
-/* Do not pass gzip flag to writeTarFile() */
-#define writeTarFile(tar_fd, verboseFlag, recurseFlags, include, exclude, gzip) \
-       writeTarFile(tar_fd, verboseFlag, recurseFlags, include, exclude)
-#endif
+#define INIT_G() do { setup_common_bufsiz(); } while (0)
 
 
 #if ENABLE_FEATURE_TAR_CREATE
@@ -210,6 +278,23 @@ static void chksum_and_xwrite(int fd, struct tar_header_t* hp)
        xwrite(fd, hp, sizeof(*hp));
 }
 
+static void replace_symlink_placeholders(llist_t *list)
+{
+       while (list) {
+               char *target;
+
+               target = list->data + strlen(list->data) + 1;
+               if (symlink(target, list->data)) {
+                       /* shared message */
+                       bb_error_msg_and_die("can't create %slink '%s' to '%s'",
+                               "sym",
+                               list->data, target
+                       );
+               }
+               list = list->link;
+       }
+}
+
 #if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
 static void writeLongname(int fd, int type, const char *name, int dir)
 {
@@ -443,8 +528,8 @@ static int FAST_FUNC writeFileToTarball(const char *fileName, struct stat *statb
        /*
         * Check to see if we are dealing with a hard link.
         * If so -
-        * Treat the first occurance of a given dev/inode as a file while
-        * treating any additional occurances as hard links.  This is done
+        * Treat the first occurrence of a given dev/inode as a file while
+        * treating any additional occurrences as hard links.  This is done
         * by adding the file information to the HardLinkInfo linked list.
         */
        tbInfo->hlInfo = NULL;
@@ -522,21 +607,12 @@ static int FAST_FUNC writeFileToTarball(const char *fileName, struct stat *statb
        return TRUE;
 }
 
-#if ENABLE_FEATURE_SEAMLESS_GZ || ENABLE_FEATURE_SEAMLESS_BZ2
-# if !(ENABLE_FEATURE_SEAMLESS_GZ && ENABLE_FEATURE_SEAMLESS_BZ2)
-#  define vfork_compressor(tar_fd, gzip) vfork_compressor(tar_fd)
-# endif
+#if SEAMLESS_COMPRESSION
 /* Don't inline: vfork scares gcc and pessimizes code */
-static void NOINLINE vfork_compressor(int tar_fd, int gzip)
+static void NOINLINE vfork_compressor(int tar_fd, const char *gzip)
 {
        pid_t gzipPid;
-# if ENABLE_FEATURE_SEAMLESS_GZ && ENABLE_FEATURE_SEAMLESS_BZ2
-       const char *zip_exec = (gzip == 1) ? "gzip" : "bzip2";
-# elif ENABLE_FEATURE_SEAMLESS_GZ
-       const char *zip_exec = "gzip";
-# else /* only ENABLE_FEATURE_SEAMLESS_BZ2 */
-       const char *zip_exec = "bzip2";
-# endif
+
        // On Linux, vfork never unpauses parent early, although standard
        // allows for that. Do we want to waste bytes checking for it?
 # define WAIT_FOR_CHILD 0
@@ -550,11 +626,6 @@ static void NOINLINE vfork_compressor(int tar_fd, int gzip)
 
        signal(SIGPIPE, SIG_IGN); /* we only want EPIPE on errors */
 
-# if defined(__GNUC__) && __GNUC__
-       /* Avoid vfork clobbering */
-       (void) &zip_exec;
-# endif
-
        gzipPid = xvfork();
 
        if (gzipPid == 0) {
@@ -570,7 +641,7 @@ static void NOINLINE vfork_compressor(int tar_fd, int gzip)
                xmove_fd(gzipDataPipe.rd, 0);
                xmove_fd(tar_fd, 1);
                /* exec gzip/bzip2 program/applet */
-               BB_EXECLP(zip_exec, zip_exec, "-f", (char *)0);
+               BB_EXECLP(gzip, gzip, "-f", (char *)0);
                vfork_exec_errno = errno;
                _exit(EXIT_FAILURE);
        }
@@ -593,16 +664,21 @@ static void NOINLINE vfork_compressor(int tar_fd, int gzip)
 # endif
        if (vfork_exec_errno) {
                errno = vfork_exec_errno;
-               bb_perror_msg_and_die("can't execute '%s'", zip_exec);
+               bb_perror_msg_and_die("can't execute '%s'", gzip);
        }
 }
-#endif /* ENABLE_FEATURE_SEAMLESS_GZ || ENABLE_FEATURE_SEAMLESS_BZ2 */
+#endif /* SEAMLESS_COMPRESSION */
 
 
+#if !SEAMLESS_COMPRESSION
+/* Do not pass gzip flag to writeTarFile() */
+#define writeTarFile(tar_fd, verboseFlag, recurseFlags, include, exclude, gzip) \
+       writeTarFile(tar_fd, verboseFlag, recurseFlags, include, exclude)
+#endif
 /* gcc 4.2.1 inlines it, making code bigger */
 static NOINLINE int writeTarFile(int tar_fd, int verboseFlag,
        int recurseFlags, const llist_t *include,
-       const llist_t *exclude, int gzip)
+       const llist_t *exclude, const char *gzip)
 {
        int errorFlag = FALSE;
        struct TarBallInfo tbInfo;
@@ -615,7 +691,7 @@ static NOINLINE int writeTarFile(int tar_fd, int verboseFlag,
         * can avoid including the tarball into itself....  */
        xfstat(tbInfo.tarFd, &tbInfo.tarFileStatBuf, "can't stat tar file");
 
-#if ENABLE_FEATURE_SEAMLESS_GZ || ENABLE_FEATURE_SEAMLESS_BZ2
+#if SEAMLESS_COMPRESSION
        if (gzip)
                vfork_compressor(tbInfo.tarFd, gzip);
 #endif
@@ -650,7 +726,7 @@ static NOINLINE int writeTarFile(int tar_fd, int verboseFlag,
        if (errorFlag)
                bb_error_msg("error exit delayed from previous errors");
 
-#if ENABLE_FEATURE_SEAMLESS_GZ || ENABLE_FEATURE_SEAMLESS_BZ2
+#if SEAMLESS_COMPRESSION
        if (gzip) {
                int status;
                if (safe_waitpid(-1, &status, 0) == -1)
@@ -662,11 +738,9 @@ static NOINLINE int writeTarFile(int tar_fd, int verboseFlag,
 #endif
        return errorFlag;
 }
-#else
-int writeTarFile(int tar_fd, int verboseFlag,
-       int recurseFlags, const llist_t *include,
-       const llist_t *exclude, int gzip);
-#endif /* FEATURE_TAR_CREATE */
+#else /* !FEATURE_TAR_CREATE */
+# define writeTarFile(...) 0
+#endif
 
 #if ENABLE_FEATURE_TAR_FROM
 static llist_t *append_file_list_to_list(llist_t *list)
@@ -774,6 +848,7 @@ enum {
        IF_FEATURE_SEAMLESS_Z(   OPTBIT_COMPRESS    ,)
        IF_FEATURE_TAR_NOPRESERVE_TIME(OPTBIT_NOPRESERVE_TIME,)
 #if ENABLE_FEATURE_TAR_LONG_OPTIONS
+       OPTBIT_STRIP_COMPONENTS,
        OPTBIT_NORECURSION,
        IF_FEATURE_TAR_TO_COMMAND(OPTBIT_2COMMAND   ,)
        OPTBIT_NUMERIC_OWNER,
@@ -798,12 +873,13 @@ enum {
        OPT_GZIP         = IF_FEATURE_SEAMLESS_GZ(  (1 << OPTBIT_GZIP        )) + 0, // z
        OPT_XZ           = IF_FEATURE_SEAMLESS_XZ(  (1 << OPTBIT_XZ          )) + 0, // J
        OPT_COMPRESS     = IF_FEATURE_SEAMLESS_Z(   (1 << OPTBIT_COMPRESS    )) + 0, // Z
-       OPT_NOPRESERVE_TIME = IF_FEATURE_TAR_NOPRESERVE_TIME((1 << OPTBIT_NOPRESERVE_TIME)) + 0, // m
-       OPT_NORECURSION     = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NORECURSION    )) + 0, // no-recursion
-       OPT_2COMMAND        = IF_FEATURE_TAR_TO_COMMAND(  (1 << OPTBIT_2COMMAND       )) + 0, // to-command
-       OPT_NUMERIC_OWNER   = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NUMERIC_OWNER  )) + 0, // numeric-owner
-       OPT_NOPRESERVE_PERM = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NOPRESERVE_PERM)) + 0, // no-same-permissions
-       OPT_OVERWRITE       = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_OVERWRITE      )) + 0, // overwrite
+       OPT_NOPRESERVE_TIME  = IF_FEATURE_TAR_NOPRESERVE_TIME((1 << OPTBIT_NOPRESERVE_TIME)) + 0, // m
+       OPT_STRIP_COMPONENTS = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_STRIP_COMPONENTS)) + 0, // strip-components
+       OPT_NORECURSION      = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NORECURSION    )) + 0, // no-recursion
+       OPT_2COMMAND         = IF_FEATURE_TAR_TO_COMMAND(  (1 << OPTBIT_2COMMAND       )) + 0, // to-command
+       OPT_NUMERIC_OWNER    = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NUMERIC_OWNER  )) + 0, // numeric-owner
+       OPT_NOPRESERVE_PERM  = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_NOPRESERVE_PERM)) + 0, // no-same-permissions
+       OPT_OVERWRITE        = IF_FEATURE_TAR_LONG_OPTIONS((1 << OPTBIT_OVERWRITE      )) + 0, // overwrite
 
        OPT_ANY_COMPRESS = (OPT_BZIP2 | OPT_LZMA | OPT_GZIP | OPT_XZ | OPT_COMPRESS),
 };
@@ -847,6 +923,7 @@ static const char tar_longopts[] ALIGN1 =
 # if ENABLE_FEATURE_TAR_NOPRESERVE_TIME
        "touch\0"               No_argument       "m"
 # endif
+       "strip-components\0"    Required_argument "\xf9"
        "no-recursion\0"        No_argument       "\xfa"
 # if ENABLE_FEATURE_TAR_TO_COMMAND
        "to-command\0"          Required_argument "\xfb"
@@ -876,6 +953,7 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
 #if ENABLE_FEATURE_TAR_LONG_OPTIONS && ENABLE_FEATURE_TAR_FROM
        llist_t *excludes = NULL;
 #endif
+       INIT_G();
 
        /* Initialise default values */
        tar_handle = init_handle();
@@ -890,17 +968,29 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
        /* Prepend '-' to the first argument if required */
        opt_complementary = "--:" // first arg is options
                "tt:vv:" // count -t,-v
-               IF_FEATURE_TAR_FROM("X::T::") // cumulative lists
 #if ENABLE_FEATURE_TAR_LONG_OPTIONS && ENABLE_FEATURE_TAR_FROM
-               "\xff::" // cumulative lists for --exclude
+               "\xff::" // --exclude=PATTERN is a list
 #endif
                IF_FEATURE_TAR_CREATE("c:") "t:x:" // at least one of these is reqd
                IF_FEATURE_TAR_CREATE("c--tx:t--cx:x--ct") // mutually exclusive
-               IF_NOT_FEATURE_TAR_CREATE("t--x:x--t"); // mutually exclusive
+               IF_NOT_FEATURE_TAR_CREATE("t--x:x--t") // mutually exclusive
+#if ENABLE_FEATURE_TAR_LONG_OPTIONS
+               ":\xf9+" // --strip-components=NUM
+#endif
+       ;
 #if ENABLE_FEATURE_TAR_LONG_OPTIONS
        applet_long_options = tar_longopts;
 #endif
 #if ENABLE_DESKTOP
+       /* Lie to buildroot when it starts asking stupid questions. */
+       if (argv[1] && strcmp(argv[1], "--version") == 0) {
+               // Output of 'tar --version' examples:
+               // tar (GNU tar) 1.15.1
+               // tar (GNU tar) 1.25
+               // bsdtar 2.8.3 - libarchive 2.8.3
+               puts("tar (busybox) " BB_VER);
+               return 0;
+       }
        if (argv[1] && argv[1][0] != '-') {
                /* Compat:
                 * 1st argument without dash handles options with parameters
@@ -929,18 +1019,22 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
 #endif
        opt = getopt32(argv,
                "txC:f:Oopvk"
-               IF_FEATURE_TAR_CREATE(   "ch"  )
-               IF_FEATURE_SEAMLESS_BZ2( "j"   )
-               IF_FEATURE_SEAMLESS_LZMA("a"   )
-               IF_FEATURE_TAR_FROM(     "T:X:")
-               IF_FEATURE_SEAMLESS_GZ(  "z"   )
-               IF_FEATURE_SEAMLESS_XZ(  "J"   )
-               IF_FEATURE_SEAMLESS_Z(   "Z"   )
+               IF_FEATURE_TAR_CREATE(   "ch"    )
+               IF_FEATURE_SEAMLESS_BZ2( "j"     )
+               IF_FEATURE_SEAMLESS_LZMA("a"     )
+               IF_FEATURE_TAR_FROM(     "T:*X:*")
+               IF_FEATURE_SEAMLESS_GZ(  "z"     )
+               IF_FEATURE_SEAMLESS_XZ(  "J"     )
+               IF_FEATURE_SEAMLESS_Z(   "Z"     )
                IF_FEATURE_TAR_NOPRESERVE_TIME("m")
+               IF_FEATURE_TAR_LONG_OPTIONS("\xf9:") // --strip-components
                , &base_dir // -C dir
                , &tar_filename // -f filename
                IF_FEATURE_TAR_FROM(, &(tar_handle->accept)) // T
                IF_FEATURE_TAR_FROM(, &(tar_handle->reject)) // X
+#if ENABLE_FEATURE_TAR_LONG_OPTIONS
+               , &tar_handle->tar__strip_components // --strip-components
+#endif
                IF_FEATURE_TAR_TO_COMMAND(, &(tar_handle->tar__to_command)) // --to-command
 #if ENABLE_FEATURE_TAR_LONG_OPTIONS && ENABLE_FEATURE_TAR_FROM
                , &excludes // --exclude
@@ -948,11 +1042,49 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
                , &verboseFlag // combined count for -t and -v
                , &verboseFlag // combined count for -t and -v
                );
-       //bb_error_msg("opt:%08x", opt);
+#if DBG_OPTION_PARSING
+       bb_error_msg("opt: 0x%08x", opt);
+# define showopt(o) bb_error_msg("opt & %s(%x): %x", #o, o, opt & o);
+       showopt(OPT_TEST            );
+       showopt(OPT_EXTRACT         );
+       showopt(OPT_BASEDIR         );
+       showopt(OPT_TARNAME         );
+       showopt(OPT_2STDOUT         );
+       showopt(OPT_NOPRESERVE_OWNER);
+       showopt(OPT_P               );
+       showopt(OPT_VERBOSE         );
+       showopt(OPT_KEEP_OLD        );
+       showopt(OPT_CREATE          );
+       showopt(OPT_DEREFERENCE     );
+       showopt(OPT_BZIP2           );
+       showopt(OPT_LZMA            );
+       showopt(OPT_INCLUDE_FROM    );
+       showopt(OPT_EXCLUDE_FROM    );
+       showopt(OPT_GZIP            );
+       showopt(OPT_XZ              );
+       showopt(OPT_COMPRESS        );
+       showopt(OPT_NOPRESERVE_TIME );
+       showopt(OPT_STRIP_COMPONENTS);
+       showopt(OPT_NORECURSION     );
+       showopt(OPT_2COMMAND        );
+       showopt(OPT_NUMERIC_OWNER   );
+       showopt(OPT_NOPRESERVE_PERM );
+       showopt(OPT_OVERWRITE       );
+       showopt(OPT_ANY_COMPRESS    );
+       bb_error_msg("base_dir:'%s'", base_dir);
+       bb_error_msg("tar_filename:'%s'", tar_filename);
+       bb_error_msg("verboseFlag:%d", verboseFlag);
+       bb_error_msg("tar_handle->tar__to_command:'%s'", tar_handle->tar__to_command);
+       bb_error_msg("tar_handle->tar__strip_components:%u", tar_handle->tar__strip_components);
+       return 0;
+# undef showopt
+#endif
        argv += optind;
 
-       if (verboseFlag) tar_handle->action_header = header_verbose_list;
-       if (verboseFlag == 1) tar_handle->action_header = header_list;
+       if (verboseFlag)
+               tar_handle->action_header = header_verbose_list;
+       if (verboseFlag == 1)
+               tar_handle->action_header = header_list;
 
        if (opt & OPT_EXTRACT)
                tar_handle->action_data = data_extract_all;
@@ -1038,7 +1170,7 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
                         && flags == O_RDONLY
                         && !(opt & OPT_ANY_COMPRESS)
                        ) {
-                               tar_handle->src_fd = open_zipped(tar_filename);
+                               tar_handle->src_fd = open_zipped(tar_filename, /*fail_if_not_compressed:*/ 0);
                                if (tar_handle->src_fd < 0)
                                        bb_perror_msg_and_die("can't open '%s'", tar_filename);
                        } else {
@@ -1050,19 +1182,26 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
        if (base_dir)
                xchdir(base_dir);
 
-       //if (SEAMLESS_COMPRESSION || OPT_COMPRESS)
+       //if (SEAMLESS_COMPRESSION)
        //      /* We need to know whether child (gzip/bzip/etc) exits abnormally */
        //      signal(SIGCHLD, check_errors_in_children);
 
+#if ENABLE_FEATURE_TAR_CREATE
        /* Create an archive */
        if (opt & OPT_CREATE) {
-#if ENABLE_FEATURE_SEAMLESS_GZ || ENABLE_FEATURE_SEAMLESS_BZ2
-               int zipMode = 0;
-               if (ENABLE_FEATURE_SEAMLESS_GZ && (opt & OPT_GZIP))
-                       zipMode = 1;
-               if (ENABLE_FEATURE_SEAMLESS_BZ2 && (opt & OPT_BZIP2))
-                       zipMode = 2;
-#endif
+# if SEAMLESS_COMPRESSION
+               const char *zipMode = NULL;
+               if (opt & OPT_COMPRESS)
+                       zipMode = "compress";
+               if (opt & OPT_GZIP)
+                       zipMode = "gzip";
+               if (opt & OPT_BZIP2)
+                       zipMode = "bzip2";
+               if (opt & OPT_LZMA)
+                       zipMode = "lzma";
+               if (opt & OPT_XZ)
+                       zipMode = "xz";
+# endif
                /* NB: writeTarFile() closes tar_handle->src_fd */
                return writeTarFile(tar_handle->src_fd, verboseFlag,
                                (opt & OPT_DEREFERENCE ? ACTION_FOLLOWLINKS : 0)
@@ -1070,35 +1209,49 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
                                tar_handle->accept,
                                tar_handle->reject, zipMode);
        }
+#endif
 
        if (opt & OPT_ANY_COMPRESS) {
-               USE_FOR_MMU(IF_DESKTOP(long long) int FAST_FUNC (*xformer)(transformer_aux_data_t *aux, int src_fd, int dst_fd);)
+               USE_FOR_MMU(IF_DESKTOP(long long) int FAST_FUNC (*xformer)(transformer_state_t *xstate);)
                USE_FOR_NOMMU(const char *xformer_prog;)
 
-               if (opt & OPT_COMPRESS)
-                       USE_FOR_MMU(xformer = unpack_Z_stream;)
+               if (opt & OPT_COMPRESS) {
+                       USE_FOR_MMU(IF_FEATURE_SEAMLESS_Z(xformer = unpack_Z_stream;))
                        USE_FOR_NOMMU(xformer_prog = "uncompress";)
-               if (opt & OPT_GZIP)
-                       USE_FOR_MMU(xformer = unpack_gz_stream;)
+               }
+               if (opt & OPT_GZIP) {
+                       USE_FOR_MMU(IF_FEATURE_SEAMLESS_GZ(xformer = unpack_gz_stream;))
                        USE_FOR_NOMMU(xformer_prog = "gunzip";)
-               if (opt & OPT_BZIP2)
-                       USE_FOR_MMU(xformer = unpack_bz2_stream;)
+               }
+               if (opt & OPT_BZIP2) {
+                       USE_FOR_MMU(IF_FEATURE_SEAMLESS_BZ2(xformer = unpack_bz2_stream;))
                        USE_FOR_NOMMU(xformer_prog = "bunzip2";)
-               if (opt & OPT_LZMA)
-                       USE_FOR_MMU(xformer = unpack_lzma_stream;)
+               }
+               if (opt & OPT_LZMA) {
+                       USE_FOR_MMU(IF_FEATURE_SEAMLESS_LZMA(xformer = unpack_lzma_stream;))
                        USE_FOR_NOMMU(xformer_prog = "unlzma";)
-               if (opt & OPT_XZ)
-                       USE_FOR_MMU(xformer = unpack_xz_stream;)
+               }
+               if (opt & OPT_XZ) {
+                       USE_FOR_MMU(IF_FEATURE_SEAMLESS_XZ(xformer = unpack_xz_stream;))
                        USE_FOR_NOMMU(xformer_prog = "unxz";)
+               }
 
-               open_transformer_with_sig(tar_handle->src_fd, xformer, xformer_prog);
+               fork_transformer_with_sig(tar_handle->src_fd, xformer, xformer_prog);
                /* Can't lseek over pipes */
                tar_handle->seek = seek_by_read;
                /*tar_handle->offset = 0; - already is */
        }
 
+       /* Zero processed headers (== empty file) is not a valid tarball.
+        * We (ab)use bb_got_signal as exitcode here,
+        * because check_errors_in_children() uses _it_ as error indicator.
+        */
+       bb_got_signal = EXIT_FAILURE;
+
        while (get_header_tar(tar_handle) == EXIT_SUCCESS)
-               continue;
+               bb_got_signal = EXIT_SUCCESS; /* saw at least one header, good */
+
+       replace_symlink_placeholders(tar_handle->symlink_placeholders);
 
        /* Check that every file that should have been extracted was */
        while (tar_handle->accept) {
@@ -1114,8 +1267,9 @@ int tar_main(int argc UNUSED_PARAM, char **argv)
                close(tar_handle->src_fd);
 
        if (SEAMLESS_COMPRESSION || OPT_COMPRESS) {
+               /* Set bb_got_signal to 1 if a child died with !0 exitcode */
                check_errors_in_children(0);
-               return bb_got_signal;
        }
-       return EXIT_SUCCESS;
+
+       return bb_got_signal;
 }