gdb: remove get_exec_file

I believe that the get_exec_file function is unnecessary, and the code
can be simplified if we remove it.

Consider for instance when you "run" a program on Linux with native
debugging.

 1. run_command_1 obtains the executable file from
    `current_program_space->exec_filename ()`
 2. it passes it to `run_target->create_inferior()`, which is
    `inf_ptrace_target::create_inferior()` in this case, which then
    passes it to `fork_inferior()`
 3. `fork_inferior()` then has a fallback, where if the passed exec file
    is nullptr, it gets its from `get_exec_file()`.
 4. `get_exec_file()` returns `current_program_space->exec_filename ()`
    - just like the things we started with - or errors out if the
    current program space doesn't have a specified executable.

If there's no exec filename passed in step 1, there's not going to be
any in step 4, so it seems pointless to call `get_exec_file()`, we could
just error out when `exec_file` is nullptr.  But we can't error out
directly in `fork_inferior()`, since the error is GDB-specific, and that
function is shared with GDBserver.

Speaking of GDBserver, all code paths that lead to `fork_inferior()`
provide a non-nullptr exec file.

Therefore, to simplify things:

 - Make `fork_inferior()` assume that the passed exec file is not
   nullptr, don't call `get_exec_file()`
 - Change some targets (darwin-nat, go32-nat, gnu-nat, inf-ptrace,
   nto-procfs, procfs) to error out when the exec file passed to their
   create_inferior method is nullptr.  Some targets are fine with a
   nullptr exec file, so we can't check that in `run_command_1()`.
 - Add the `no_executable_specified_error()` function, which re-uses the
   error message that `get_exec_file()` had.
 - Change some targets (go32-nat, nto-procfs) to not call
   `get_exec_file()`, since it's pointless for the same reason as in the
   example above, if it returns, it's going the be the same value as the
   `exec_file` parameter.  Just rely on `exec_file`.
 - Remove the final use of `get_exec_file()`, in `load_command()`.
 - Remove the `get_exec_file()` implementations in GDB and GDBserver and
   remove the shared declaration.

Change-Id: I601c16498e455f7baa1f111a179da2f6c913baa3
Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 5 insertions, 11 deletions

diff --git a/gdb/nat/fork-inferior.c b/gdb/nat/fork-inferior.c
index 172eef0..2fd9cba 100644
--- a/gdb/nat/fork-inferior.c
+++ b/gdb/nat/fork-inferior.c
@@ -265,26 +265,20 @@ execv_argv::init_for_shell (const char *exec_file,
 /* See nat/fork-inferior.h.  */
 
 pid_t
-fork_inferior (const char *exec_file_arg, const std::string &allargs,
-	       char **env, traceme_ftype traceme_fun,
-	       init_trace_ftype init_trace_fun, pre_trace_ftype pre_trace_fun,
-	       const char *shell_file_arg, exec_ftype exec_fun)
+fork_inferior (const char *exec_file, const std::string &allargs, char **env,
+	       traceme_ftype traceme_fun, init_trace_ftype init_trace_fun,
+	       pre_trace_ftype pre_trace_fun, const char *shell_file_arg,
+	       exec_ftype exec_fun)
 {
   pid_t pid;
   /* Set debug_fork then attach to the child while it sleeps, to debug.  */
   int debug_fork = 0;
   const char *shell_file;
-  const char *exec_file;
   char **save_our_env;
   int i;
   int save_errno;
 
-  /* If no exec file handed to us, get it from the exec-file command
-     -- with a good, common error message if none is specified.  */
-  if (exec_file_arg == NULL)
-    exec_file = get_exec_file ();
-  else
-    exec_file = exec_file_arg;
+  gdb_assert (exec_file != nullptr);
 
   /* 'startup_with_shell' is declared in inferior.h and bound to the
      "set startup-with-shell" option.  If 0, we'll just do a