tool wrapper: add initial wrapper coded in C

Add an initial wrapper:
- find the realpath of the tool being called
- add the '.' in front of the tool name
- add the '/lib' dir to the base dir of the tool
- set and export LD_LIBRARY_PATH
- execve the real tool

scripts/wrapper.c

@@ -0,0 +1,128 @@
+#include <limits.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+
+
+/* Needed for execve */
+extern char **environ;
+
+int main( int argc,
+          char** argv )
+{
+  char *fullname;   /* 'fullname' is used to store the absolute path to the
+                       tool being executed; it serves as a base to compute
+                       the realname of that tool, and the directory holding
+                       our runtime libraries */
+  char *realname;   /* 'realname' is the real name of the tool, that is what
+                       the wrapper is currently impersonating */
+  char *basedir;    /* 'libdir' contains our runtime libraries */
+
+  char *lastslash;  /* Temporary variables now */
+  char *ldlibpath;
+  size_t len;
+  int execve_ret;
+
+  /* In case we have a relative or absolute pathname (ie. contains a slash),
+   * then realpath wll work. But if the tool was found in the PATH, realpath
+   * won't work, and we'll have to search ourselves.
+   * This if{}else{} block allocates memory for fullname. */
+  if( strchr( argv[0], '/' ) ) {
+    fullname = (char*) malloc( PATH_MAX * sizeof(char) );
+    if( ! realpath( argv[0], fullname ) ) {
+      perror( "tool wrapper" );
+      exit( 1 );
+    }
+  } else {
+    char *path;
+    char *mypath;
+    char *colon;
+    char *testname;
+    struct stat st;
+
+    fullname = NULL;
+    colon = mypath = path = strdup( getenv( "PATH" ) );
+    while( colon ) {
+      colon = strchr( mypath, ':' );
+      if( colon ) {
+        *colon = '\0';
+      }
+      testname = strdup( mypath );
+      testname = (char*) realloc( testname,   strlen( testname )
+                                            + strlen( argv[0] )
+                                            + 2 * sizeof(char) );
+      memset( testname + strlen( testname ),
+              0,
+              strlen( argv[0] ) + 2 * sizeof(char) );
+      strcat( testname, "/" );
+      strcat( testname, argv[0] );
+      if( stat( testname, &st ) == 0 ) {
+        /* OK, exists. Is it a regular file, or a
+         * symlink, which the current user may execute? */
+        if( S_ISREG( st.st_mode ) && ! access( testname, X_OK || R_OK ) ) {
+          fullname = strdup( testname );
+          break;
+        }
+      }
+      free( testname );
+      mypath = colon + 1;
+    }
+    free( path );
+    if( ! fullname ) {
+      fprintf( stderr, "tool wrapper: %s: command not found\n", argv[0] );
+      exit( 1 );
+    }
+  }
+
+  /* Duplicate my own name to add the 'dot' to tool name */
+  realname = strdup( fullname );
+  realname = (char*) realloc( realname, strlen( realname) + 2 * sizeof(char) );
+  realname[ strlen( realname ) + 1 ] = '\0';
+
+  /* Add the dot after the last '/' */
+  lastslash = strrchr( realname, '/' );
+  memmove( lastslash + 1, lastslash, strlen( lastslash ) );
+  *( lastslash + 1 ) = '.';
+
+  /* Compute the basedir of the tool */
+  basedir = strdup( fullname );
+  lastslash = strrchr( basedir, '/' );
+  *lastslash = '\0';
+  lastslash = strrchr( basedir, '/' );
+  *lastslash = '\0';
+
+  /* Append '/lib' */
+  len = strlen( basedir );
+  basedir = (char*) realloc( basedir, len + 5 );
+  *( basedir + len ) = '\0';
+  strcat( basedir, "/lib" );
+
+  /* Now add the directory with our runtime libraries to the
+     front of the library search path, LD_LIBRARY_PATH */
+  ldlibpath = getenv( "LD_LIBRARY_PATH" );
+  if( ldlibpath ) {
+    basedir = (char*) realloc( basedir,   strlen( basedir )
+                                        + strlen( ldlibpath )
+                                        + 2 * sizeof(char) );
+    strcat( basedir, ":" );
+    strcat( basedir, ldlibpath );
+  }
+
+  if( setenv( "LD_LIBRARY_PATH", basedir, 1 ) ) {
+    errno = ENOMEM;
+    perror( "tool wrapper" );
+    exit( 1 );
+  }
+
+  /* Execute the real tool, now */
+  execve_ret = execve( realname, argv, environ );
+
+  /* In case something went wrong above, print a
+     diagnostic message, and exit with error code 1 */
+  perror( "tool wrapper" );
+  return 1;
+}