builder: Use libelf to detect elf files

This additionally looks for already stripped files

builder/Makefile.am.inc

@@ -32,6 +32,6 @@ xdg_app_builder_SOURCES = \
 	builder/builder-utils.h \
 	$(NULL)
 
-xdg_app_builder_LDADD = $(BASE_LIBS) $(OSTREE_LIBS) $(JSON_LIBS) $(SOUP_LIBS) $(LIBARCHIVE_LIBS) libglnx.la libxdgapp-common.la
+xdg_app_builder_LDADD = $(BASE_LIBS) $(OSTREE_LIBS) $(JSON_LIBS) $(SOUP_LIBS) $(LIBARCHIVE_LIBS) $(LIBELF_LIBS) \
+			libglnx.la libxdgapp-common.la
 xdg_app_builder_CFLAGS = $(BASE_CFLAGS) $(OSTREE_CFLAGS) $(JSON_CFLAGS) $(SOUP_CFLAGS) $(LIBARCHIVE_CFLAGS)
-

builder/builder-manifest.c

@@ -736,20 +736,6 @@ builder_manifest_build (BuilderManifest *self,
   return TRUE;
 }
 
-static gboolean
-strip (GError **error,
-       ...)
-{
-  gboolean res;
-  va_list ap;
-
-  va_start (ap, error);
-  res = xdg_app_spawn (NULL, NULL, error, "strip", ap);
-  va_end (ap);
-
-  return res;
-}
-
 static gboolean
 command (GFile *app_dir,
          char **env_vars,
@@ -794,54 +780,6 @@ command (GFile *app_dir,
   return TRUE;
 }
 
-guint16
-read_elf_16(guchar *ptr, guint16 endianness)
-{
-  guint16 lo, hi;
-  if (endianness == 1)
-    {
-      lo = ptr[0];
-      hi = ptr[1];
-    }
-  else
-    {
-      lo = ptr[1];
-      hi = ptr[0];
-    }
-  return lo  | (hi << 8);
-}
-
-static gboolean
-is_elf (int fd, gboolean *is_shared)
-{
-  guchar elf_magic[4] = { 0x7f, 'E', 'L', 'F' };
-  guchar header[64];
-  gssize r;
-  guint8 endianness;
-  guint16 e_type;
-
-  r = read (fd, header, sizeof (header));
-  if (r != sizeof (header))
-    return FALSE;
-
-  if (memcmp (header, elf_magic, 4) != 0)
-    return FALSE;
-
-  endianness = header[0x5];
-  if (endianness != 1 && endianness != 2) /* 1 == little, 2 == big endian */
-    return FALSE;
-
-  e_type = read_elf_16 (&header[0x10], endianness);
-
-  /* Only handle executable (2) or shared (3) */
-  if (e_type != 2 && e_type != 3)
-    return FALSE;
-
-  *is_shared = (e_type == 3);
-
-  return TRUE;
-}
-
 typedef gboolean (*ForeachFileFunc) (BuilderManifest *self,
                                      int            source_parent_fd,
                                      const char    *source_name,
@@ -929,40 +867,33 @@ foreach_file (BuilderManifest *self,
 
 static gboolean
 strip_file_cb (BuilderManifest *self,
-              int            source_parent_fd,
-              const char    *source_name,
-              const char    *full_dir,
-              const char    *rel_dir,
-              struct stat   *stbuf,
-              gboolean      *found,
-              int            depth,
-              GError       **error)
+               int            source_parent_fd,
+               const char    *source_name,
+               const char    *full_dir,
+               const char    *rel_dir,
+               struct stat   *stbuf,
+               gboolean      *found,
+               int            depth,
+               GError       **error)
 {
-  if (S_ISREG (stbuf->st_mode) &&
-      ((strstr (source_name, ".so.") != NULL || g_str_has_suffix (source_name, ".so")) ||
-       (stbuf->st_mode & 0111) != 0))
+  if (S_ISREG (stbuf->st_mode))
     {
-      glnx_fd_close int fd = -1;
+      g_autofree char *path = g_strconcat (full_dir, "/", source_name, NULL);
+      gboolean is_shared, is_stripped;
 
-      fd = openat (source_parent_fd, source_name, O_RDONLY|O_NOFOLLOW|O_CLOEXEC);
-      if (fd >= 0)
+      if (is_elf_file (path, &is_shared, &is_stripped) && !is_stripped)
         {
-          gboolean is_shared;
-          if (is_elf (fd, &is_shared))
+          g_autofree char *rel_path = g_strconcat (rel_dir, "/", source_name, NULL);
+          g_print ("stripping: %s\n", rel_path);
+          if (is_shared)
             {
-              g_autofree char *path = g_strconcat (full_dir, "/", source_name, NULL);
-              g_autofree char *rel_path = g_strconcat (rel_dir, "/", source_name, NULL);
-              g_print ("stripping: %s\n", rel_path);
-              if (is_shared)
-                {
-                  if (!strip (error, "--remove-section=.comment", "--remove-section=.note", "--strip-unneeded", path, NULL))
-                    return FALSE;
-                }
-              else
-                {
-                  if (!strip (error, "--remove-section=.comment", "--remove-section=.note", path, NULL))
-                    return FALSE;
-                }
+              if (!strip (error, "--remove-section=.comment", "--remove-section=.note", "--strip-unneeded", path, NULL))
+                return FALSE;
+            }
+          else
+            {
+              if (!strip (error, "--remove-section=.comment", "--remove-section=.note", path, NULL))
+                return FALSE;
             }
         }
     }

builder/builder-utils.c

@@ -21,8 +21,13 @@
 
 #include "config.h"
 
+#include <libelf.h>
+#include <gelf.h>
+#include <sys/mman.h>
+
 #include <string.h>
 
+#include "xdg-app-utils.h"
 #include "builder-utils.h"
 
 char *
@@ -113,3 +118,89 @@ path_prefix_match (const char *pattern,
     }
   return NULL; /* Should not be reached */
 }
+
+gboolean
+strip (GError **error,
+       ...)
+{
+  gboolean res;
+  va_list ap;
+
+  va_start (ap, error);
+  res = xdg_app_spawn (NULL, NULL, error, "strip", ap);
+  va_end (ap);
+
+  return res;
+}
+
+static gboolean elf_has_symtab (Elf *elf)
+{
+  Elf_Scn *scn;
+  GElf_Shdr shdr;
+
+  scn = NULL;
+  while ((scn = elf_nextscn(elf, scn)) != NULL)
+    {
+      if (gelf_getshdr (scn, &shdr) == NULL)
+        continue;
+
+      if (shdr.sh_type != SHT_SYMTAB)
+        continue;
+
+      return TRUE;
+    }
+
+  return FALSE;
+}
+
+gboolean is_elf_file (const char *path,
+                      gboolean *is_shared,
+                      gboolean *is_stripped)
+{
+  g_autofree char *filename = g_path_get_basename (path);
+  struct stat stbuf;
+
+  if (lstat (path, &stbuf) == -1)
+    return FALSE;
+
+  if (!S_ISREG (stbuf.st_mode))
+    return FALSE;
+
+  if ((strstr (filename, ".so.") != NULL ||
+       g_str_has_suffix (filename, ".so")) ||
+      (stbuf.st_mode & 0111) != 0)
+    {
+      glnx_fd_close int fd = -1;
+
+      fd = open (path, O_RDONLY|O_NOFOLLOW|O_CLOEXEC);
+      if (fd >= 0)
+        {
+          Elf *elf;
+          GElf_Ehdr ehdr;
+          gboolean res = FALSE;
+
+          if (elf_version (EV_CURRENT) == EV_NONE )
+            return FALSE;
+
+          elf = elf_begin (fd, ELF_C_READ, NULL);
+          if (elf == NULL)
+            return FALSE;
+
+          if (elf_kind (elf) == ELF_K_ELF &&
+              gelf_getehdr (elf, &ehdr))
+            {
+              if (is_shared)
+                *is_shared = ehdr.e_type == ET_DYN;
+              if (is_stripped)
+                *is_stripped = !elf_has_symtab (elf);
+
+              res = TRUE;
+            }
+
+          elf_end (elf);
+          return res;
+        }
+    }
+
+  return FALSE;
+}

builder/builder-utils.h

@@ -33,6 +33,13 @@ char *builder_uri_to_filename (const char *uri);
 const char *path_prefix_match (const char *pattern,
                                const char *string);
 
+gboolean strip (GError **error,
+                ...);
+
+gboolean is_elf_file (const char *path,
+                      gboolean *is_shared,
+                      gboolean *is_stripped);
+
 G_END_DECLS
 
 #endif /* __BUILDER_UTILS_H__ */

configure.ac

@@ -177,7 +177,27 @@ AS_IF([ test x$with_libarchive != xno ], [
 ], [ with_libarchive=no ])
 AM_CONDITIONAL(USE_LIBARCHIVE, test $with_libarchive != no)
 
+dnl ************************
+dnl *** check for libelf ***
+dnl ************************
+PKG_CHECK_MODULES([LIBELF], [libelf >= 0.8.12], [have_libelf=yes], [have_libelf=maybe])
+AS_IF([ test $have_libelf = maybe ], [
+  save_LIBS=$LIBS
+  AC_CHECK_LIB([elf], [elf_begin], [:], [have_libelf=no])
+  AC_CHECK_LIB([elf], [elf_getshdrstrndx], [:], [have_libelf=no])
+  AC_CHECK_LIB([elf], [elf_getshdrnum], [:], [have_libelf=no])
+  AC_CHECK_HEADER([libelf.h], [:], [have_libelf=no])
+  LIBS=$save_LIBS
 
+  if test $have_libelf != no; then
+    LIBELF_LIBS=-lelf
+    have_libelf=yes
+  fi
+])
+
+if test x$have_libelf != xyes; then
+  AC_MSG_ERROR([libelf not found])
+fi
 AC_ARG_ENABLE(documentation,
               AC_HELP_STRING([--enable-documentation], [Build documentation]),,
               enable_documentation=yes)