[RFA] Fine tune exec-file-mismatch help and documentation.

[Philippe Waroquiers <philippe.waroquiers@skynet.be>]

It was deemed better to explicitly mention in help and doc that build IDs
are used for comparison, and that symbols are loaded when asking to
load the exec-file.

gdb/ChangeLog
2020-06-27  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* exec.c (_initialize_exec): Update exec-file-mismatch help.

gdb/doc/ChangeLog
2020-06-27  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.texinfo (Attach): Updte exec-file-mismatch doc.
---
 gdb/doc/gdb.texinfo | 2 ++
 gdb/exec.c          | 8 ++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index fbe9f850af..142684b694 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -3016,6 +3016,8 @@ by @value{GDBN} and the executable file used to start the process.  If
 @samp{ask}, the default, display a warning and ask the user whether to
 load the process executable file; if @samp{warn}, just display a
 warning; if @samp{off}, don't attempt to detect a mismatch.
+If the user asks to load the process ececutable file, then its symbols
+will be loaded as well.
 
 @cindex show exec-file-mismatch
 @item show exec-file-mismatch
diff --git a/gdb/exec.c b/gdb/exec.c
index de473fbcb2..84e75e0798 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -305,7 +305,7 @@ validate_exec_file (int from_tty)
 	exec_file_target = TARGET_SYSROOT_PREFIX + exec_file_target;
 
       warning
-	(_("Mismatch between current exec-file %ps\n"
+	(_("Build ID mismatch between current exec-file %ps\n"
 	   "and automatically determined exec-file %ps\n"
 	   "exec-file-mismatch handling is currently \"%s\""),
 	 styled_string (file_name_style.style (), current_exec_file),
@@ -1269,7 +1269,11 @@ loaded by GDB and the exec-file automatically determined when attaching\n\
 to a process:\n\n\
  ask  - warn the user and ask whether to load the determined exec-file.\n\
  warn - warn the user, but do not change the exec-file.\n\
- off  - do not check for mismatch."),
+ off  - do not check for mismatch.\n\
+\n\
+GDB detects a mismatch by comparing the build IDs of the files.\n\
+If the user asks to load the determined exec-file, then its symbols\n\
+will be loaded as well."),
 			set_exec_file_mismatch_command,
 			show_exec_file_mismatch_command,
 			&setlist, &showlist);
-- 
2.20.1