[PATCH v2 2/2] Make gdbserver work with filename-only binaries

[Sergio Durigan Junior <sergiodj at redhat dot com>]

Changes from v1:

- Moved "is_regular_file" from "source.c" to "common/common-utils.c".

- Made "adjust_program_name_path" use "is_regular_file" in order to
  check if there is a file named PROGRAM_NAME in CWD, and prefix it
  with CURRENT_DIRECTORY if it exists.  Otherwise, don't prefix it and
  let gdbserver try to find the binary in $PATH.


Simon mentioned on IRC that, after the startup-with-shell feature has
been implemented on gdbserver, it is not possible to specify a
filename-only binary, like:

  $ gdbserver :1234 a.out
  /bin/bash: line 0: exec: a.out: not found
  During startup program exited with code 127.
  Exiting

This happens on systems where the current directory "." is not listed
in the PATH environment variable.  Although include "." in the PATH
variable is a possible workaround, this can be considered a regression
because before startup-with-shell it was possible to use only the
filename (due to reason that gdbserver used "exec*" directly).

The idea of the patch is to perform a call to "gdb_abspath" and adjust
the PROGRAM_NAME variable before the call to "create_inferior".  This
adjustment will consist of tilde-expansion or prefixing PROGRAM_NAME
using the CURRENT_DIRECTORY (a variable that was specific to GDB, but
has been put into common/common-defs.h and now is set/used by
gdbserver as well), thus transforming PROGRAM_NAME in an absolute
path.

This mimicks the behaviour seen on GDB (look at "openp" and
"attach_inferior", for example).  Now, we'll always execute the binary
using its full path on gdbserver.

I am also submitting a testcase which exercises the scenario described
above.  Because the test requires copying (and deleting) files
locally, I decided to restrict its execution to non-remote
targets/hosts.  I've also had to do a minor adjustment on
gdb.server/non-existing-program.exp's regexp in order to match the
correct error message.

Built and regtested on BuildBot, without regressions.

gdb/gdbserver/ChangeLog:
2018-02-12  Sergio Durigan Junior  <sergiodj@redhat.com>

	* common/common-utils.c: Include "sys/stat.h".
	(is_regular_file): Move here from "source.c"; change return
	type to "bool".
	* common/common-utils.h (is_regular_file): New prototype.
	* source.c: Don't include "sys/stat.h".
	(is_regular_file): Move to "common/common-utils.c".

gdb/gdbserver/ChangeLog:
2018-02-12  Sergio Durigan Junior  <sergiodj@redhat.com>

	* server.c: Include "filenames.h" and "pathstuff.h".
	(adjust_program_name_path): New function.
	(attach_inferior): Call "adjust_program_name_path" before
	"create_inferior".
	(captured_main): Likewise.
	(process_serial_event): Likewise.

gdb/testsuite/ChangeLog:
2018-02-12  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.server/abspath.exp: New file.
---
 gdb/common/common-utils.c            | 32 +++++++++++++++++++++
 gdb/common/common-utils.h            |  5 ++++
 gdb/gdbserver/server.c               | 33 ++++++++++++++++++++++
 gdb/source.c                         | 34 -----------------------
 gdb/testsuite/gdb.server/abspath.exp | 54 ++++++++++++++++++++++++++++++++++++
 5 files changed, 124 insertions(+), 34 deletions(-)
 create mode 100644 gdb/testsuite/gdb.server/abspath.exp

diff --git a/gdb/common/common-utils.c b/gdb/common/common-utils.c
index ae2dd9db2b..aa403d8088 100644
--- a/gdb/common/common-utils.c
+++ b/gdb/common/common-utils.c
@@ -20,6 +20,7 @@
 #include "common-defs.h"
 #include "common-utils.h"
 #include "host-defs.h"
+#include <sys/stat.h>
 #include <ctype.h>
 
 /* The xmalloc() (libiberty.h) family of memory management routines.
@@ -408,3 +409,34 @@ stringify_argv (const std::vector<char *> &args)
 
   return ret;
 }
+
+/* See common/common-utils.h.  */
+
+bool
+is_regular_file (const char *name, int *errno_ptr)
+{
+  struct stat st;
+  const int status = stat (name, &st);
+
+  /* Stat should never fail except when the file does not exist.
+     If stat fails, analyze the source of error and return True
+     unless the file does not exist, to avoid returning false results
+     on obscure systems where stat does not work as expected.  */
+
+  if (status != 0)
+    {
+      if (errno != ENOENT)
+	return true;
+      *errno_ptr = ENOENT;
+      return false;
+    }
+
+  if (S_ISREG (st.st_mode))
+    return true;
+
+  if (S_ISDIR (st.st_mode))
+    *errno_ptr = EISDIR;
+  else
+    *errno_ptr = EINVAL;
+  return false;
+}
diff --git a/gdb/common/common-utils.h b/gdb/common/common-utils.h
index 2320318de7..888396637e 100644
--- a/gdb/common/common-utils.h
+++ b/gdb/common/common-utils.h
@@ -146,4 +146,9 @@ in_inclusive_range (T value, T low, T high)
   return value >= low && value <= high;
 }
 
+/* Return True if the file NAME exists and is a regular file.
+   If the result is false then *ERRNO_PTR is set to a useful value assuming
+   we're expecting a regular file.  */
+extern bool is_regular_file (const char *name, int *errno_ptr);
+
 #endif
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index f931273fa3..24b3e4d4ad 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -39,6 +39,8 @@
 #include "common-inferior.h"
 #include "job-control.h"
 #include "environ.h"
+#include "filenames.h"
+#include "pathstuff.h"
 
 #include "common/selftest.h"
 
@@ -283,6 +285,31 @@ get_environ ()
   return &our_environ;
 }
 
+/* Verify if PROGRAM_NAME is an absolute path, and perform path
+   adjustment/expansion if not.  */
+
+static void
+adjust_program_name_path ()
+{
+  /* Make sure we're using the absolute path of the inferior when
+     creating it.  */
+  if (!IS_ABSOLUTE_PATH (program_name))
+    {
+      int reg_file_errno;
+
+      /* Check if the file is in our CWD.  If it is, then we prefix
+	 its name with CURRENT_DIRECTORY.  Otherwise, we leave the
+	 name as-is because we'll try searching for it in $PATH.  */
+      if (is_regular_file (program_name, &reg_file_errno))
+	{
+	  char *tmp_program_name = program_name;
+
+	  program_name = gdb_abspath (program_name).release ();
+	  xfree (tmp_program_name);
+	}
+    }
+}
+
 static int
 attach_inferior (int pid)
 {
@@ -3016,6 +3043,8 @@ handle_v_run (char *own_buf)
       program_name = new_program_name;
     }
 
+  adjust_program_name_path ();
+
   /* Free the old argv and install the new one.  */
   free_vector_argv (program_args);
   program_args = new_argv;
@@ -3770,6 +3799,8 @@ captured_main (int argc, char *argv[])
 	program_args.push_back (xstrdup (next_arg[i]));
       program_args.push_back (NULL);
 
+      adjust_program_name_path ();
+
       /* Wait till we are at first instruction in program.  */
       create_inferior (program_name, program_args);
 
@@ -4290,6 +4321,8 @@ process_serial_event (void)
 	  /* Wait till we are at 1st instruction in prog.  */
 	  if (program_name != NULL)
 	    {
+	      adjust_program_name_path ();
+
 	      create_inferior (program_name, program_args);
 
 	      if (last_status.kind == TARGET_WAITKIND_STOPPED)
diff --git a/gdb/source.c b/gdb/source.c
index 77f5e8d4d4..bfa9fd6e4c 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -29,7 +29,6 @@
 #include "filestuff.h"
 
 #include <sys/types.h>
-#include <sys/stat.h>
 #include <fcntl.h>
 #include "gdbcore.h"
 #include "gdb_regex.h"
@@ -670,39 +669,6 @@ info_source_command (const char *ignore, int from_tty)
 }
 
 
-/* Return True if the file NAME exists and is a regular file.
-   If the result is false then *ERRNO_PTR is set to a useful value assuming
-   we're expecting a regular file.  */
-
-static int
-is_regular_file (const char *name, int *errno_ptr)
-{
-  struct stat st;
-  const int status = stat (name, &st);
-
-  /* Stat should never fail except when the file does not exist.
-     If stat fails, analyze the source of error and return True
-     unless the file does not exist, to avoid returning false results
-     on obscure systems where stat does not work as expected.  */
-
-  if (status != 0)
-    {
-      if (errno != ENOENT)
-	return 1;
-      *errno_ptr = ENOENT;
-      return 0;
-    }
-
-  if (S_ISREG (st.st_mode))
-    return 1;
-
-  if (S_ISDIR (st.st_mode))
-    *errno_ptr = EISDIR;
-  else
-    *errno_ptr = EINVAL;
-  return 0;
-}
-
 /* Open a file named STRING, searching path PATH (dir names sep by some char)
    using mode MODE in the calls to open.  You cannot use this function to
    create files (O_CREAT).
diff --git a/gdb/testsuite/gdb.server/abspath.exp b/gdb/testsuite/gdb.server/abspath.exp
new file mode 100644
index 0000000000..fbde5ee537
--- /dev/null
+++ b/gdb/testsuite/gdb.server/abspath.exp
@@ -0,0 +1,54 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2018 Free Software Foundation, Inc.
+
+# This program 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.
+#
+# This program 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/>.
+
+# Test that gdbserver performs path expansion/adjustment when we
+# provide just a filename (without any path specifications) to it.
+
+load_lib gdbserver-support.exp
+
+standard_testfile normal.c
+
+if { [skip_gdbserver_tests] } {
+    return 0
+}
+
+# We only test things locally, and on native-gdbserver
+if { [is_remote target] || [is_remote host] || ![use_gdb_stub] } {
+    return 0
+}
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile debug] } {
+    return -1
+}
+
+set target_exec [gdbserver_download_current_prog]
+set target_execname [file tail $target_exec]
+# We temporarily copy the file to our current directory
+file copy -force $target_exec [pwd]
+set res [gdbserver_start "" $target_execname]
+
+set gdbserver_protocol [lindex $res 0]
+set gdbserver_gdbport [lindex $res 1]
+gdb_target_cmd $gdbserver_protocol $gdbserver_gdbport
+
+if { [runto_main] } {
+    pass "load filename without absolute path"
+} else {
+    fail "load filename without absolute path"
+}
+
+file delete -force "[pwd]/$target_execname"
-- 
2.14.3