bug#29020: 25.1; gdb-mi doesn't display prompt when attaching

bug#29020: 25.1; gdb-mi doesn't display prompt when attaching

[Mike Gulick]

When attaching to a process from gdb-mi, the (gdb) prompt is not shown
after the attach command completes.

This creates confusion because it appears that GDB is still working.  A
common reaction is to hit 'Enter', which re-sends the last command,
i.e. 'attach PID', which kills the process that you were attempting to
debug.

$ gdb --version
GNU gdb (Debian 7.12-6) 7.12.0.20161007-git

$ sleep 1000 &
[1] 9924

$ emacs -Q

M-x gdb
Run gdb (like this): gdb -i=mi -n

*gud* buffer output:

  Current directory is /usr/share/emacs/25.1/lisp/progmodes/
  GNU gdb (Debian 7.12-6) 7.12.0.20161007-git
  ...
  (gdb) attach 9924
  Attaching to process 9924
  (gdb) Reading symbols from /bin/sleep...(no debugging symbols found)...done.
  Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug/.build-id/79/450f6e36287865d093ea209b85a222209925ff.debug...done.
  done.
  Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/.build-id/6f/150f33b150d6a81e26a425dd47d713d00f2d29.debug...done.
  done.
  0x00007f8f29196230 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84
  84	../sysdeps/unix/syscall-template.S: No such file or directory.

Notice that the prompt is displayed after "Attaching to process 9924",
but it is then obscured by additional information printed by gdb.

The gdb-mi output (captured by running 'set logging on' from gdb
prompt'):

  (gdb) 
  ~"Attaching to process 31331\n"
  =thread-group-started,id="i1",pid="31331"
  =thread-created,id="1",group-id="i1"
  ^done
  ~"Reading symbols from /bin/sleep..."
  ~"(no debugging symbols found)...done.\n"
  =library-loaded,id="/lib/x86_64-linux-gnu/libc.so.6",target-name="/lib/x86_64-linux-gnu/libc.so.6",host-name="/lib/x86_64-linux-gnu/libc.so.6",symbols-loaded="0",thread-group="i1"
  =library-loaded,id="/lib64/ld-linux-x86-64.so.2",target-name="/lib64/ld-linux-x86-64.so.2",host-name="/lib64/ld-linux-x86-64.so.2",symbols-loaded="0",thread-group="i1"
  ~"Reading symbols from /lib/x86_64-linux-gnu/libc.so.6..."
  ~"Reading symbols from /usr/lib/debug/.build-id/79/450f6e36287865d093ea209b85a222209925ff.debug..."
  ~"done.\n"
  ~"done.\n"
  ~"Reading symbols from /lib64/ld-linux-x86-64.so.2..."
  ~"Reading symbols from /usr/lib/debug/.build-id/6f/150f33b150d6a81e26a425dd47d713d00f2d29.debug..."
  ~"done.\n"
  ~"done.\n"
  ~"0x00007f8d63e86230 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84\n"
  &"84\t../sysdeps/unix/syscall-template.S: No such file or directory.\n"
  *stopped,frame={addr="0x00007f8d63e86230",func="__nanosleep_nocancel",args=[],file="../sysdeps/unix/syscall-template.S",fullname="/build/glibc-p3Km7c/glibc-2.24/posix/../sysdeps/unix/syscall-template.S",line="84"},thread-id="1",stopped-threads="all",core="9"
  33^done,frame={level="0",addr="0x00007f8d63e86230",func="__nanosleep_nocancel",file="../sysdeps/unix/syscall-template.S",fullname="/build/glibc-p3Km7c/glibc-2.24/posix/../sysdeps/unix/syscall-template.S",line="84"}
  (gdb) 
  34^done,threads=[{id="1",target-id="process 31331",name="sleep",frame={level="0",addr="0x00007f8d63e86230",func="__nanosleep_nocancel",args=[],file="../sysdeps/unix/syscall-template.S",fullname="/build/glibc-p3Km7c/glibc-2.24/posix/../sysdeps/unix/syscall-template.S",line="84"},state="stopped",core="9"}],current-thread-id="1"
  (gdb) 
  35^done,BreakpointTable={nr_rows="0",nr_cols="6",hdr=[{width="7",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[]}
  (gdb) 
  36^done,register-names=["rax","rbx","rcx","rdx","rsi","rdi","rbp","rsp","r8","r9","r10","r11","r12","r13","r14","r15","rip","eflags","cs","ss","ds","es","fs","gs","st0","st1","st2","st3","st4","st5","st6","st7","fctrl","fstat","ftag","fiseg","fioff","foseg","fooff","fop","xmm0","xmm1","xmm2","xmm3","xmm4","xmm5","xmm6","xmm7","xmm8","xmm9","xmm10","xmm11","xmm12","xmm13","xmm14","xmm15","mxcsr","ymm0h","ymm1h","ymm2h","ymm3h","ymm4h","ymm5h","ymm6h","ymm7h","ymm8h","ymm9h","ymm10h","ymm11h","ymm12h","ymm13h","ymm14h","ymm15h","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","","orig_rax","al","bl","cl","dl","sil","dil","bpl","spl","r8l","r9l","r10l","r11l","r12l","r13l","r14l","r15l","ah","bh","ch","dh","ax","bx","cx","dx","si","di","bp","","r8w","r9w","r10w","r11w","r12w","r13w","r14w","r15w","eax","ebx","ecx","edx","esi","edi","ebp","esp","r8d","r9d","r10d","r11d","r12d","r13d","r14d","r15d","ymm0","ymm1","ymm2","ymm3","ymm4","ymm5","ymm6","ymm7","ymm8","ymm9","ymm10","ymm11","ymm12","ymm13","ymm14","ymm15"]
  (gdb) 

In gdb-mi.el, the variable 'gdb-first-done-or-error' is set to nil after
the first '^done' is printed.  When parsing '*stopped' in gdb-stopped,
the prompt is only printed if gdb-first-done-or-error is 't'.  Since
this output stream contains '^done', followed by some more output,
followed by '*stopped', the gdb prompt is not being re-printed when
'*stopped' is encountered.  If I temporarily change the following lines
in gdb-stopped in gdb-mi.el, then the prompt is printed after attaching:

--- /tmp/gdb-mi.el.orig	2017-10-26 17:26:27.955626830 -0400
+++ /tmp/gdb-mi.el	2017-10-26 17:25:27.715228866 -0400
@@ -2537,8 +2537,7 @@
           (message "Thread %s stopped" thread-id))))
 
     ;; Print "(gdb)" to GUD console
-    (when gdb-first-done-or-error
-      (setq gdb-filter-output (concat gdb-filter-output gdb-prompt-name)))
+    (setq gdb-filter-output (concat gdb-filter-output gdb-prompt-name))
 
     ;; In non-stop, we update information as soon as another thread gets
     ;; stopped

This naive change may have other side-effects, which I did not fully
think through, but it does at least show what the issue is.  Another
possible solution is that 'gdb-first-done-or-error', which controls
whether the prompt should be printed on the next '^done', '^error', or
'*stopped', should be reset to 't' whenever anything is printed to the
gud buffer.  However I was unable to figure out how to make that work.

Thanks for your consideration.

-Mike

In GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-09-15, modified by Debian built on trouble
Windowing system distributor 'The X.Org Foundation', version 11.0.11903000
System Description:	Debian GNU/Linux 9.1 (stretch)

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --with-x=yes --with-x-toolkit=gtk3
 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs25-wN2qS3/emacs25-25.1+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Debugger

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Auto-saving...
Auto-saving gdb-mi.el.gz: Opening output file: Permission denied, /usr/share/emacs/25.1/lisp/progmodes/#gdb-mi.el.gz#
Quit
C-; is undefined
Undo!
Mark set [2 times]
gdb-stopped
Target doesn’t support non-stop mode.  Turning it off.
Switched to thread 1
ptrace: No such process.

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util help-fns mail-prsvr mail-utils
jka-compr thingatpt find-func cl-seq gdb-mi bindat json map seq byte-opt
gv bytecomp byte-compile cl-extra help-mode easymenu cconv cl-loaddefs
pcase cl-lib gud easy-mmode comint ansi-color ring time-date mule-util
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel x-win term/common-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment elisp-mode lisp-mode prog-mode register
page menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock
font-lock syntax facemenu font-core frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote dbusbind inotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 108410 11828)
 (symbols 48 21790 0)
 (miscs 40 75 270)
 (strings 32 21724 5215)
 (string-bytes 1 614894)
 (vectors 16 15131)
 (vector-slots 8 463120 6883)
 (floats 8 192 261)
 (intervals 56 756 11)
 (buffers 976 20))

bug#29020: [PATCH] gdb-mi doesn't display prompt when attaching

[Mike Gulick]

This patch is pretty straightforward.  When we write a console message
to the GUD buffer, we now reset a variable that is used to determine
whether to print the gdb prompt on the next '^done' or '*stopped'
message.

diff --git a/lisp/progmodes/gdb-mi.el b/lisp/progmodes/gdb-mi.el
index 7723f70..fb6e1a5 100644
--- a/lisp/progmodes/gdb-mi.el
+++ b/lisp/progmodes/gdb-mi.el
@@ -2188,7 +2188,10 @@ a GDB/MI reply message."
 
 (defun gdbmi-bnf-console-stream-output (c-string)
   "Handler for the console-stream-output GDB/MI output grammar rule."
-  (gdb-console c-string))
+  (gdb-console c-string)
+  ;; We've written to the GUD console, so we should print the prompt after the
+  ;; next result-class or async-class.
+  (setq gdb-first-done-or-error t))
 
 (defun gdbmi-bnf-target-stream-output (_c-string)
   "Handler for the target-stream-output GDB/MI output grammar rule."

bug#29020: [PATCH] gdb-mi doesn't display prompt when attaching

[Eli Zaretskii]

> From: Mike Gulick <mike.gulick@mathworks.com>
> Date: Fri, 27 Oct 2017 11:28:00 -0400
> 
> This patch is pretty straightforward.  When we write a console message
> to the GUD buffer, we now reset a variable that is used to determine
> whether to print the gdb prompt on the next '^done' or '*stopped'
> message.

Thanks, but could you please also provide a recipe that would
demonstrate the effect of this change?

bug#29020: [PATCH] gdb-mi doesn't display prompt when attaching

[Mike Gulick]

On 10/27/2017 01:35 PM, Eli Zaretskii wrote:
>> From: Mike Gulick <mike.gulick@mathworks.com>
>> Date: Fri, 27 Oct 2017 11:28:00 -0400
>>
>> This patch is pretty straightforward.  When we write a console message
>> to the GUD buffer, we now reset a variable that is used to determine
>> whether to print the gdb prompt on the next '^done' or '*stopped'
>> message.
> 
> Thanks, but could you please also provide a recipe that would
> demonstrate the effect of this change?
> 

Hi Eli,

Is the example I provided in the bug report sufficient?

E.g.

1) In shell:

$ sleep 1000 &
[1] 9924    # <--- NOTE PID

2) In shell:

$ emacs -Q

3) In emacs
M-x gdb
Run gdb (like this): gdb -i=mi -n

4) In *gud* buffer
(gdb) attach 9924   # <--- PID from earlier

5) Observe that (gdb) prompt is not displayed after output from GDB

With the patch, the (gdb) prompt will be displayed, e.g.

  (gdb) attach 9924
  Attaching to process 9924
  (gdb) Reading symbols from /bin/sleep...(no debugging symbols found)...done.
  Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug/.build-id/79/450f6e36287865d093ea209b85a222209925ff.debug...done.
  done.
  Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/.build-id/6f/150f33b150d6a81e26a425dd47d713d00f2d29.debug...done.
  done.
  0x00007f8f29196230 in __nanosleep_nocancel () at ../sysdeps/unix/syscall-template.S:84
  84	../sysdeps/unix/syscall-template.S: No such file or directory.
  (gdb) 

Thanks,
Mike

bug#29020: [PATCH] gdb-mi doesn't display prompt when attaching

[Eli Zaretskii]

> Cc: 29020@debbugs.gnu.org
> From: Mike Gulick <mike.gulick@mathworks.com>
> Date: Mon, 30 Oct 2017 10:23:49 -0400
> 
> > Thanks, but could you please also provide a recipe that would
> > demonstrate the effect of this change?
> > 
> 
> Hi Eli,
> 
> Is the example I provided in the bug report sufficient?

Sorry, I failed to notice your original report, and only saw the one
to which I replied.  I will now look at the OP, thanks.

bug#29020: [PATCH] gdb-mi doesn't display prompt when attaching

[Eli Zaretskii]

> Date: Mon, 30 Oct 2017 20:23:51 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 29020@debbugs.gnu.org
> 
> > Cc: 29020@debbugs.gnu.org
> > From: Mike Gulick <mike.gulick@mathworks.com>
> > Date: Mon, 30 Oct 2017 10:23:49 -0400
> > 
> > > Thanks, but could you please also provide a recipe that would
> > > demonstrate the effect of this change?
> > > 
> > 
> > Hi Eli,
> > 
> > Is the example I provided in the bug report sufficient?
> 
> Sorry, I failed to notice your original report, and only saw the one
> to which I replied.  I will now look at the OP, thanks.

Thanks, I've pushed your changes to the emacs-26 branch.