[PATCH] elfclassify tool

[Florian Weimer <fweimer at redhat dot com>]

This patch adds an elfclassify tool, mainly for the benefit of RPM's
find-debuginfo.sh.

I still need to implement an --unstripped option and fix the iteration
over the dynamic section.

Suggestions for improving the argp/help output are welcome as well.  I'm
not familiar with argp at all.

I'm keeping a branch with these changes here:

  <https://pagure.io/fweimer/elfutils/commits/elfclassify>

Thanks,
Florian

diff --git a/src/Makefile.am b/src/Makefile.am
index 2b1c0dcb..966d1da7 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -26,7 +26,8 @@ AM_CPPFLAGS += -I$(srcdir)/../libelf -I$(srcdir)/../libebl \
 AM_LDFLAGS = -Wl,-rpath-link,../libelf:../libdw
 
 bin_PROGRAMS = readelf nm size strip elflint findtextrel addr2line \
-	       elfcmp objdump ranlib strings ar unstrip stack elfcompress
+	       elfcmp objdump ranlib strings ar unstrip stack elfcompress \
+	       elfclassify
 
 noinst_LIBRARIES = libar.a
 
@@ -83,6 +84,7 @@ ar_LDADD = libar.a $(libelf) $(libeu) $(argp_LDADD)
 unstrip_LDADD = $(libebl) $(libelf) $(libdw) $(libeu) $(argp_LDADD) -ldl
 stack_LDADD = $(libebl) $(libelf) $(libdw) $(libeu) $(argp_LDADD) -ldl $(demanglelib)
 elfcompress_LDADD = $(libebl) $(libelf) $(libdw) $(libeu) $(argp_LDADD)
+elfclassify_LDADD = $(libelf) $(libeu) $(argp_LDADD)
 
 installcheck-binPROGRAMS: $(bin_PROGRAMS)
 	bad=0; pid=$$$$; list="$(bin_PROGRAMS)"; for p in $$list; do \
diff --git a/src/elfclassify.c b/src/elfclassify.c
new file mode 100644
index 00000000..ead3260b
--- /dev/null
+++ b/src/elfclassify.c
@@ -0,0 +1,387 @@
+/* Classification of ELF files.
+   Copyright (C) 2019 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file 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; either version 3 of the License, or
+   (at your option) any later version.
+
+   elfutils 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/>.  */
+
+#include <config.h>
+
+#include <argp.h>
+#include <error.h>
+#include <fcntl.h>
+#include <gelf.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#include ELFUTILS_HEADER(elf)
+#include "printversion.h"
+
+/* Name and version of program.  */
+ARGP_PROGRAM_VERSION_HOOK_DEF = print_version;
+
+/* Bug report address.  */
+ARGP_PROGRAM_BUG_ADDRESS_DEF = PACKAGE_BUGREPORT;
+
+enum classify_command
+{
+  classify_file = 1000,
+  classify_elf,
+  classify_executable,
+  classify_shared,
+  classify_loadable
+};
+
+/* Set by parse_opt.  */
+static enum classify_command command;
+static const char *command_path;
+static int verbose;
+
+/* Set by map_file.  */
+static int file_fd = -1;
+
+static void
+open_file (void)
+{
+  if (verbose > 1)
+    fprintf (stderr, "debug: processing file: %s\n", command_path);
+
+  file_fd = open (command_path, O_RDONLY);
+  if (file_fd < 0)
+    {
+      if (errno == ENOENT)
+        exit (1);
+      else
+        error (2, errno, N_("opening %s"), command_path);
+    }
+  struct stat st;
+  if (fstat (file_fd, &st) != 0)
+    error (2, errno, N_("reading %s\n"), command_path);
+  if (!S_ISREG (st.st_mode))
+    exit (1);
+}
+
+/* Set by open_elf.  */
+static Elf *elf;
+
+static void
+open_elf (void)
+{
+  open_file ();
+  elf = elf_begin (file_fd, ELF_C_READ, NULL);
+  if (elf == NULL)
+    error (2, 0, "%s: %s", command_path, elf_errmsg (-1));
+  if (elf_kind (elf) != ELF_K_ELF && elf_kind (elf) != ELF_K_AR)
+    exit (1);
+}
+
+static int elf_type;
+static bool has_program_interpreter;
+static bool has_dynamic;
+static bool has_soname;
+static bool has_pie_flag;
+static bool has_dt_debug;
+
+static void
+run_classify (void)
+{
+  if (elf_kind (elf) != ELF_K_ELF)
+    return;
+
+  GElf_Ehdr ehdr_storage;
+  GElf_Ehdr *ehdr = gelf_getehdr (elf, &ehdr_storage);
+  if (ehdr == NULL)
+    exit (1);
+  elf_type = ehdr->e_type;
+
+  /* Examine program headers.  */
+  {
+    size_t nphdrs;
+    if (elf_getphdrnum (elf, &nphdrs) != 0)
+      error (2, 0, "%s: program header: %s", command_path, elf_errmsg (-1));
+    if (nphdrs > INT_MAX)
+      error (2, 0, "%s: number of program headers is too large: %zu",
+             command_path, nphdrs);
+    for (size_t phdr_idx = 0; phdr_idx < nphdrs; ++phdr_idx)
+      {
+        GElf_Phdr phdr_storage;
+        GElf_Phdr *phdr = gelf_getphdr (elf, phdr_idx, &phdr_storage);
+        if (phdr == NULL)
+          error (2, 0, "%s: %s", command_path, elf_errmsg (-1));
+        if (phdr->p_type == PT_DYNAMIC)
+          has_dynamic = true;
+        if (phdr->p_type == PT_INTERP)
+          has_program_interpreter = true;
+      }
+  }
+
+  /* Examine the dynamic section.  */
+  if (has_dynamic)
+    {
+      Elf_Scn *dyn_section = NULL;
+      {
+        Elf_Scn *scn = NULL;
+        while (true)
+          {
+            scn = elf_nextscn (elf, scn);
+            if (scn == NULL)
+              break;
+            GElf_Shdr shdr_storage;
+            GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_storage);
+            if (shdr == NULL)
+              error (2, 0, N_("could not obtain section header: %s"),
+                     elf_errmsg (-1));
+            if (verbose > 2)
+              fprintf (stderr, "debug: section header %d found\n",
+                       shdr->sh_type);
+            if (shdr->sh_type == SHT_DYNAMIC)
+              {
+                if (verbose > 1)
+                  fputs ("debug: dynamic section found", stderr);
+                dyn_section = scn;
+                break;
+              }
+          }
+      }
+      if (dyn_section != NULL)
+        {
+          Elf_Data *data = elf_getdata (dyn_section, NULL);
+          if (verbose > 2)
+            fprintf (stderr, "debug: Elf_Data for dynamic section: %p\n",
+                     data);
+
+          if (data != NULL)
+            for (int dyn_idx = 0; ; ++dyn_idx)
+              {
+                GElf_Dyn dyn_storage;
+                GElf_Dyn *dyn = gelf_getdyn (data, dyn_idx, &dyn_storage);
+                if (dyn == NULL)
+                  break;
+                if (verbose > 2)
+                  fprintf (stderr, "debug: dynamic entry %d"
+                           " with tag %llu found\n",
+                           dyn_idx, (unsigned long long int) dyn->d_tag);
+                if (dyn->d_tag == DT_SONAME)
+                  has_soname = true;
+                if (dyn->d_tag == DT_FLAGS_1 && (dyn->d_un.d_val & DF_1_PIE))
+                  has_pie_flag = true;
+                if (dyn->d_tag == DT_DEBUG)
+                  has_dt_debug = true;
+                if (dyn->d_tag == DT_NULL)
+                  break;
+              }
+        }
+    }
+
+  if (verbose)
+    {
+      fprintf (stderr, "info: ELF type: %d\n", elf_type);
+      if (has_program_interpreter)
+        fputs ("info: program interpreter found\n", stderr);
+      if (has_dynamic)
+        fputs ("info: dynamic segment found\n", stderr);
+      if (has_soname)
+        fputs ("info: soname found\n", stderr);
+      if (has_pie_flag)
+        fputs ("info: PIE flag found\n", stderr);
+      if (has_dt_debug)
+        fputs ("info: DT_DEBUG found\n", stderr);
+    }
+}
+
+/* Return true if the file is a loadable object, which basically means
+   it is an ELF file, but not a relocatable object file.  (The kernel
+   and various userspace components can load ET_REL files, but we
+   disregard that for our classification purposes.)  */
+static bool
+is_loadable (void)
+{
+  return elf_kind (elf) == ELF_K_ELF && elf_type != ET_REL;
+}
+
+static bool
+is_shared (void)
+{
+  if (!is_loadable ())
+    return false;
+
+  /* The ELF type is very clear: this is an executable.  */
+  if (elf_type == ET_EXEC)
+    return false;
+
+  /* If the object is marked as PIE, it is definitely an executable,
+     and not a loadlable shared object.  */
+  if (has_pie_flag)
+    return false;
+
+  /* Treat a DT_SONAME tag as a strong indicator that this is a shared
+     object.  */
+  if (has_soname)
+    return true;
+
+  /* This is probably a PIE program: there is no soname, but a program
+     interpreter.  In theory, this file could be also  */
+  if (has_program_interpreter)
+    return false;
+
+  /* Roland McGrath mentions in
+     <https://www.sourceware.org/ml/libc-alpha/2015-03/msg00605.html>,
+     that “we defined a PIE as an ET_DYN with a DT_DEBUG”.  This
+     matches current binutils behavior (version 2.32).  DT_DEBUG is
+     added if bfd_link_executable returns true or if bfd_link_pic
+     returns false, depending on the architectures.  However, DT_DEBUG
+     is not documented as being specific to executables, therefore use
+     it only as a low-priority discriminator.  */
+  if (has_dt_debug)
+    return false;
+
+  /* If there is no dynamic section, the file cannot be loaded as a
+     shared object.  */
+  if (!has_dynamic)
+    return false;
+  return true;
+}
+
+static bool
+is_executable (void)
+{
+  if (!is_loadable ())
+    return false;
+
+  /* A loadable object which is not a shared object is treated as an
+     executable.  */
+  return !is_shared ();
+}
+
+static error_t
+parse_opt (int key, char *arg, struct argp_state *state)
+{
+  switch (key)
+    {
+    case classify_file:
+    case classify_elf:
+    case classify_executable:
+    case classify_shared:
+    case classify_loadable:
+      command = key;
+      command_path = arg;
+      break;
+
+    case 'v':
+      ++verbose;
+      break;
+
+    case ARGP_KEY_ARG:
+      argp_usage (state);
+      exit (2);
+    }
+
+  return 0;
+}
+
+int
+main (int argc, char **argv)
+{
+  const struct argp_option options[] =
+    {
+      { "file", classify_file, "PATH", 0,
+        N_("Check PATH is file that can be read"), 0 },
+      { "elf", classify_elf, "PATH", 0,
+        N_("Check if the file at PATH is a valid ELF object"), 0 },
+      { "executable", classify_executable, "PATH", 0,
+        N_("Check if the file at PATH is an ELF program executable"), 0 },
+      { "shared", classify_shared, "PATH", 0,
+        N_("Check if the file at PATH is an ELF shared object (DSO)"), 0 },
+      { "loadable", classify_loadable, "PATH", 0,
+        N_("Check if the file at PATH is a loadable object (program or shared object)"), 0 },
+      { "verbose", 'v', NULL, 0,
+        N_("Output additional information (can be specified multiple times)"), 0 },
+      { NULL, 0, NULL, 0, NULL, 0 }
+    };
+
+  const struct argp argp =
+    {
+      .options = options,
+      .parser = parse_opt,
+      .doc = N_("Determine the type of an ELF file.")
+    };
+
+  if (argp_parse (&argp, argc, argv, ARGP_NO_EXIT, NULL, NULL) != 0)
+    return 2;
+
+  elf_version (EV_CURRENT);
+
+  switch (command)
+    {
+    case classify_file:
+      open_file ();
+      return 0;
+    case classify_elf:
+      open_elf ();
+      return 0;
+
+    case classify_executable:
+      open_elf ();
+      run_classify ();
+      if (is_executable ())
+        {
+          if (verbose)
+            fputs ("info: executable\n", stderr);
+          return 0;
+        }
+      else
+        {
+          if (verbose)
+            fputs ("info: not an executable\n", stderr);
+          return 1;
+        }
+
+    case classify_shared:
+      open_elf ();
+      run_classify ();
+      if (is_shared ())
+        {
+          if (verbose)
+            fputs ("info: shared object\n", stderr);
+          return 0;
+        }
+      else
+        {
+          if (verbose)
+            fputs ("info: not a shared object\n", stderr);
+          return 1;
+        }
+
+    case classify_loadable:
+      open_elf ();
+      run_classify ();
+      if (is_loadable ())
+        {
+          if (verbose)
+            fputs ("info: loadable object\n", stderr);
+          return 0;
+        }
+      else
+        {
+          if (verbose)
+            fputs ("info: not a loadable object\n", stderr);
+          return 1;
+        }
+    }
+
+  return 2;
+}