[RFA] Fixes PR 25475: ensure exec-file-mismatch "ask" always asks in case of mismatch.

[Philippe Waroquiers]

As explained in https://sourceware.org/bugzilla/show_bug.cgi?id=25475,
when the currently loaded file has no debug symbol,
symbol_file_add_with_addrs does not ask a confirmation to the user
before loading the new symbol file.  The behaviour is not consistent
when symbol_file_add_with_addrs is called due to exec-file-mismatch "ask"
setting.

The PR discusses several solutions/approaches.
The preferred approach (suggested by Joel) is to ensure that GDB always asks
a confirmation when it loads a new symbol file due to exec-file-mismatch,
using a new SYMFILE add-flag.

I tested this manually.  If OK, we can remove the bypass introduced by Tom
in 6b9374f1, in order to always answer to the 'load' question.

gdb/ChangeLog
YYYY-MM-DD  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* symfile-add-flags.h: New flag SYMFILE_ALWAYS_CONFIRM.
	* exec.c (validate_exec_file): If from_tty, set both
	SYMFILE_VERBOSE (== from_tty) and SYMFILE_ALWAYS_CONFIRM.
	* symfile.c (symbol_file_add_with_addrs): if always_confirm
	and from_tty, unconditionally ask a confirmation.
---
 gdb/exec.c              |  5 ++++-
 gdb/symfile-add-flags.h |  6 ++++++
 gdb/symfile.c           | 10 ++++++----
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/gdb/exec.c b/gdb/exec.c
index fa770c6f02..de473fbcb2 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -315,7 +315,10 @@ validate_exec_file (int from_tty)
 	{
 	  symfile_add_flags add_flags = SYMFILE_MAINLINE;
 	  if (from_tty)
-	    add_flags |= SYMFILE_VERBOSE;
+	    {
+	      add_flags |= SYMFILE_VERBOSE;
+	      add_flags |= SYMFILE_ALWAYS_CONFIRM;
+	    }
 	  try
 	    {
 	      symbol_file_add_main (exec_file_target.c_str (), add_flags);
diff --git a/gdb/symfile-add-flags.h b/gdb/symfile-add-flags.h
index 740357bc12..2b2c2e68f2 100644
--- a/gdb/symfile-add-flags.h
+++ b/gdb/symfile-add-flags.h
@@ -44,6 +44,12 @@ enum symfile_add_flag : unsigned
 
     /* The new objfile should be marked OBJF_NOT_FILENAME.  */
     SYMFILE_NOT_FILENAME = 1 << 5,
+
+    /* If SYMFILE_VERBOSE (interpreted as from_tty) and SYMFILE_ALWAYS_CONFIRM,
+       always ask user to confirm loading the symbol file.
+       Without this flag, symbol_file_add_with_addrs asks a confirmation only
+       for a main symbol file replacing a file having symbols.  */
+    SYMFILE_ALWAYS_CONFIRM = 1 << 6,
  };
 
 DEF_ENUM_FLAGS_TYPE (enum symfile_add_flag, symfile_add_flags);
diff --git a/gdb/symfile.c b/gdb/symfile.c
index b29f864b37..0e2310176f 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1051,6 +1051,7 @@ symbol_file_add_with_addrs (bfd *abfd, const char *name,
   struct objfile *objfile;
   const int from_tty = add_flags & SYMFILE_VERBOSE;
   const int mainline = add_flags & SYMFILE_MAINLINE;
+  const int always_confirm = add_flags & SYMFILE_ALWAYS_CONFIRM;
   const int should_print = (print_symbol_loading_p (from_tty, mainline, 1)
 			    && (readnow_symbol_files
 				|| (add_flags & SYMFILE_NO_READ) == 0));
@@ -1069,12 +1070,13 @@ symbol_file_add_with_addrs (bfd *abfd, const char *name,
   if ((add_flags & SYMFILE_NOT_FILENAME) != 0)
     flags |= OBJF_NOT_FILENAME;
 
-  /* Give user a chance to burp if we'd be
+  /* Give user a chance to burp if always_confirm or we'd be
      interactively wiping out any existing symbols.  */
 
-  if ((have_full_symbols () || have_partial_symbols ())
-      && mainline
-      && from_tty
+  if (from_tty
+      && (always_confirm
+	  || ((have_full_symbols () || have_partial_symbols ())
+	      && mainline))
       && !query (_("Load new symbol table from \"%s\"? "), name))
     error (_("Not confirmed."));
 
-- 
2.20.1