Re: [External] : Re: [PATCH v3] gdb : Signal to pstack/gdb kills the attached process.

[Partha Satapathy <partha.satapathy@oracle.com>]

On 3/5/2024 2:17 PM, Guinevere Larsen wrote:
> On 19/02/2024 06:10, Partha Satapathy wrote:
>> On 1/24/2024 8:49 PM, Partha Satapathy wrote:
>>> On 1/10/2024 9:29 PM, Partha Satapathy wrote:
>>>> On 12/5/2023 6:43 PM, Guinevere Larsen wrote:
>>>>> On 17/11/2023 15:48, Partha Satapathy wrote:
>>>>>> On 11/6/2023 7:08 PM, Guinevere Larsen wrote:
>>>>>>> On 02/11/2023 19:27, Partha Satapathy wrote:
>>>>>>>> On 11/2/2023 11:54 PM, Partha Satapathy wrote:
>>>>>>>>> On 10/25/2023 9:24 PM, Guinevere Larsen wrote:
>>>>>>>>>> Hi!
>>>>>>>>>>
>>>>>>>>>> Thanks for working on this issue, and sorry about the delay in 
>>>>>>>>>> getting this reviewed. For future reference, we (at least I) 
>>>>>>>>>> tend to try and go for patches with many pings, so it is 
>>>>>>>>>> better to ping existing patches than re-sending them :)
>>>>>>>>>
>>>>>>>>> I some how missed this mail, hence a delay in reply.
>>>>>>>>> I sorry for this and unfortunately have made the mistake once 
>>>>>>>>> again.
>>>>>>>>> Hope the extra threads can be deleted and I will keep my 
>>>>>>>>> discussion bound to this thread.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I'm not very knowledgeable on how GDB does signal handling, so 
>>>>>>>>>> I'm going to review this patch at face value. I hope someone 
>>>>>>>>>> who does know how this part works gets a look at this soon!
>>>>>>>>>>
>>>>>>>>>> On 16/10/2023 11:28, Partha Satapathy wrote:
>>>>>>>>>>> Problem :
>>>>>>>>>>> While gdb attaching a target, If ctrl-c pressed in the midst 
>>>>>>>>>>> of the process attach,  the sigint is passed to the debugged 
>>>>>>>>>>> process. This triggers exit of the debugged.
>>>>>>>>>>>
>>>>>>>>>>> Let’s take the example of pstack,  which dumps the stack of 
>>>>>>>>>>> all threads in a process. In some cases printing of stack can 
>>>>>>>>>>> take significant time and ctrl-c is pressed to abort 
>>>>>>>>>>> pstack/gdb application. This in turn kills the debugged 
>>>>>>>>>>> process, which can be critical for the system. In this case 
>>>>>>>>>>> the intention of “ctrl+c” to kill pstack/gdb, but not the 
>>>>>>>>>>> target application.
>>>>>>>>>>>
>>>>>>>>>>> Reproduction:
>>>>>>>>>>>
>>>>>>>>>>> The debugged application generally attached to process by:
>>>>>>>>>>> gdb -p <<pid>>
>>>>>>>>>>> or gdb /proc/<<pid>>/exe pid
>>>>>>>>>>> pstack uses the latter  method to attach the debugged to gdb. 
>>>>>>>>>>> If the application is large or process of reading symbols is 
>>>>>>>>>>> slow, gives a good window to press the ctrl+c during attach. 
>>>>>>>>>>> Spawning "gdb" under "strace -k" makes gdb a lot slower and 
>>>>>>>>>>> gives a larger window to easily press the
>>>>>>>>>>> ctrl+c at the precise period i.e. during the attach of the 
>>>>>>>>>>> debugged
>>>>>>>>>>> process. The above strace hack will enhance rate of 
>>>>>>>>>>> reproduction of the issue. Testcase:
>>>>>>>>>>>
>>>>>>>>>>> With GDB 13.1
>>>>>>>>>>> ps aux | grep abrtd
>>>>>>>>>>> root     2195168   /usr/sbin/abrtd -d -s
>>>>>>>>>>>
>>>>>>>>>>> #strace -k -o log gdb -p 2195168
>>>>>>>>>>> Attaching to process 2195168
>>>>>>>>>>> [New LWP 2195177]
>>>>>>>>>>> [New LWP 2195179]
>>>>>>>>>>> ^C[Thread debugging using libthread_db enabled]
>>>>>>>>>>> <<<<   Note the ctrl+c is pressed after attach is initiated 
>>>>>>>>>>> and it’s
>>>>>>>>>>> still reading the symbols from library >>>> Using host 
>>>>>>>>>>> libthread_db library "/lib64/libthread_db.so.1".
>>>>>>>>>>> 0x00007fe3ed6d70d1 in poll () from /lib64/libc.so.6
>>>>>>>>>>> (gdb) q
>>>>>>>>>>> A debugging session is active.
>>>>>>>>>>>           Inferior 1 [process 2195168] will be detached Quit 
>>>>>>>>>>> anyway? (y or n) y Detaching from program: /usr/sbin/abrtd, 
>>>>>>>>>>> process 2195168
>>>>>>>>>>>
>>>>>>>>>>> # ps aux | grep 2195168
>>>>>>>>>>> <<<< Process exited >>>>
>>>>>>>>>>>
>>>>>>>>>>> Description:
>>>>>>>>>>>
>>>>>>>>>>> We are installing a signal handler in gdb that marks the 
>>>>>>>>>>> Ctrl-c/sigint received by gdb. GDB passes this sigint to the 
>>>>>>>>>>> debugged at some definite points during the window of process 
>>>>>>>>>>> attach. The process of attaching debugged involves steps like 
>>>>>>>>>>> PTRACE_ATTACH , reading symbols, getting the stop signal from 
>>>>>>>>>>> the debugged and get ready with GDB prompt. Note:
>>>>>>>>>>> one of the example of this is sigint passing is:
>>>>>>>>>>> "     - installs a SIGINT handler that forwards SIGINT to the 
>>>>>>>>>>> inferior.
>>>>>>>>>>>          Otherwise a Ctrl-C pressed just while waiting for 
>>>>>>>>>>> the initial
>>>>>>>>>>>          stop would end up as a spurious Quit.
>>>>>>>>>>> "
>>>>>>>>>>>
>>>>>>>>>>> There are few other places where sigint is passed to the 
>>>>>>>>>>> debugged during attach of process to gdb. As the debugger and 
>>>>>>>>>>> debugged are not fully attached during this period, the 
>>>>>>>>>>> sigint takes its default action and terminates the process.
>>>>>>>>>>>
>>>>>>>>>>> Solution:
>>>>>>>>>>>
>>>>>>>>>>> While gdb attaches process, the target is not the current 
>>>>>>>>>>> session leader. Hence, until attach is complete and GDB 
>>>>>>>>>>> prompt is availed, the sigint should not be passed to the 
>>>>>>>>>>> debugged. A similar approach is taken for "gdb) run &". In 
>>>>>>>>>>> target_terminal::inferior()
>>>>>>>>>>>     /* A background resume (``run&'') should leave GDB in 
>>>>>>>>>>> control of the
>>>>>>>>>>>        terminal.  */
>>>>>>>>>>>     if (ui->prompt_state != PROMPT_BLOCKED)
>>>>>>>>>>>       return;
>>>>>>>>>>>
>>>>>>>>>>> The passing of signal is skipped if the process ran in 
>>>>>>>>>>> background. With this approach we can skip passing the sigint 
>>>>>>>>>>> if the process is attached to gdb and process attach is not 
>>>>>>>>>>> complete.
>>>>>>>>>>> Here is the proposed solution:
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Fix :
>>>>>>>>>>>
>>>>>>>>>>> While gdb attaching a target, If ctrl-c/sigint pressed in the 
>>>>>>>>>>> midst of the process attach, the sigint is passed to the 
>>>>>>>>>>> debugged process.
>>>>>>>>>>> This triggers exit of the debugged.
>>>>>>>>>>>
>>>>>>>>>>> This issue is evident while getting the process stack with 
>>>>>>>>>>> ./gdb --quiet -nx  -ex 'set width 0' -ex 'set height 0'
>>>>>>>>>>> -ex 'set pagination no' -ex 'set confirm off'
>>>>>>>>>>> -ex 'thread apply all bt' -ex quit /proc/<PID>/exe <PID> and 
>>>>>>>>>>> press the ctrl+c while attach.
>>>>>>>>>>>
>>>>>>>>>>> The above method is also used in pstack application which is 
>>>>>>>>>>> a wrapper over gdb to print the process stack. A Ctrl+C 
>>>>>>>>>>> intended to kill gdb or pstack, but kills the debugged even 
>>>>>>>>>>> if it is attached and not spawned by gdb.
>>>>>>>>>>
>>>>>>>>>> This is a very good description of the error you've 
>>>>>>>>>> encountered, but given the repetition on this "fix:" part, I'm 
>>>>>>>>>> wondering, what is meant to be the commit message? Is it just 
>>>>>>>>>> these last few lines, or is it the whole thing? If it is just 
>>>>>>>>>> this last bit, I think it would benefit from some more 
>>>>>>>>>> explanation of the solution. If it is the whole message, I 
>>>>>>>>>> think you can reduce a bit the repetition.
>>>>>>>>>>
>>>>>>>>>> Also, at many points you say "debugged process" and "target". 
>>>>>>>>>> In GDB-land we call that the "inferior". Target has a very 
>>>>>>>>>> specific meaning in the context of GDB (roughly the CPU you're 
>>>>>>>>>> running, and some extra bits here and there).
>>>>>>>>>>
>>>>>>>>>> I also have a few comments on the specific changes, that are 
>>>>>>>>>> inlined.
>>>>>>>>>>
>>>>>>>>>>> ---
>>>>>>>>>>>   gdb/inferior.h | 3 +++
>>>>>>>>>>>   gdb/target.c   | 4 ++++
>>>>>>>>>>>   gdb/top.c      | 2 ++
>>>>>>>>>>>   3 files changed, 9 insertions(+)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/gdb/inferior.h b/gdb/inferior.h index 
>>>>>>>>>>> 4d001b0ad50e..b7048d10bbe4 100644
>>>>>>>>>>> --- a/gdb/inferior.h
>>>>>>>>>>> +++ b/gdb/inferior.h
>>>>>>>>>>> @@ -557,6 +557,9 @@ class inferior : public refcounted_object,
>>>>>>>>>>>     /* True if this child process was attached rather than 
>>>>>>>>>>> forked.  */
>>>>>>>>>>>     bool attach_flag = false;
>>>>>>>>>>>
>>>>>>>>>>> +  /* True if target process synced and gdb ui is out of 
>>>>>>>>>>> block. */ bool
>>>>>>>>>>
>>>>>>>>>> This comment is oddly worded. Based on the change to 
>>>>>>>>>> gdb/top.c, I think you could reword it like this:
>>>>>>>>>>
>>>>>>>>>> /* True if inferior has been fully synced and the prompt is no 
>>>>>>>>>> longer blocked.  */
>>>>>>>>>>
>>>>>>>>>>> + sync_flag = false;
>>>>>>>>>> Typo here, the variable's type should be on this line.
>>>>>>>>>>> +
>>>>>>>>>>>     /* If this inferior is a vfork child, then this is the 
>>>>>>>>>>> pointer to
>>>>>>>>>>>        its vfork parent, if GDB is still attached to it.  */
>>>>>>>>>>>     inferior *vfork_parent = NULL;
>>>>>>>>>>> diff --git a/gdb/target.c b/gdb/target.c index 
>>>>>>>>>>> d5bfd7d0849b..f7c115497451 100644
>>>>>>>>>>> --- a/gdb/target.c
>>>>>>>>>>> +++ b/gdb/target.c
>>>>>>>>>>> @@ -3826,6 +3826,10 @@ target_pass_ctrlc (void)
>>>>>>>>>>>                   through the target_stack.  */
>>>>>>>>>>>                scoped_restore_current_inferior restore_inferior;
>>>>>>>>>>>                set_current_inferior (inf);
>>>>>>>>>>> +             if ((current_inferior()->attach_flag) &&
>>>>>>>>>>
>>>>>>>>>> A couple of style issues here: when the indentation would have 
>>>>>>>>>> 8 spaces, you should use a tab instead;
>>>>>>>>>>
>>>>>>>>>> There should be a space between the function name and the 
>>>>>>>>>> parameters;
>>>>>>>>>> And when you need to cut a logical expression in half, the 
>>>>>>>>>> operator should be at the start of a new line.
>>>>>>>>>>
>>>>>>>>>>> + !(current_inferior()->sync_flag)) {
>>>>>>>>>> In this case, since it is just one line, there is no need to 
>>>>>>>>>> have the curly braces. However, when they are needed, they 
>>>>>>>>>> should be on the following line, and 2 spaces further in 
>>>>>>>>>> indentation.
>>>>>>>>>>> + return;
>>>>>>>>>>> +             }
>>>>>>>>>>>                current_inferior ()->top_target ()->pass_ctrlc 
>>>>>>>>>>> ();
>>>>>>>>>>>                return;
>>>>>>>>>>>              }
>>>>>>>>>>> diff --git a/gdb/top.c b/gdb/top.c
>>>>>>>>>>> index 621aa6883233..26cc6caac0e5 100644
>>>>>>>>>>> --- a/gdb/top.c
>>>>>>>>>>> +++ b/gdb/top.c
>>>>>>>>>>> @@ -542,6 +542,8 @@ wait_sync_command_done (void)
>>>>>>>>>>>     while (gdb_do_one_event () >= 0)
>>>>>>>>>>>       if (ui->prompt_state != PROMPT_BLOCKED)
>>>>>>>>>>>         break;
>>>>>>>>>>> +
>>>>>>>>>>> +  current_inferior()->sync_flag = true;
>>>>>>>>>>
>>>>>>>>>> I'm not very knowledgeable on this part of GDB, so take this 
>>>>>>>>>> with a grain of salt, but I wonder if this is the best place 
>>>>>>>>>> to put this.
>>>>>>>>>>
>>>>>>>>>> Since you only set this flag as false when first creating the 
>>>>>>>>>> inferior structure, I don't see why it should be re-set every 
>>>>>>>>>> time we're waiting for a command to be done. You could set the 
>>>>>>>>>> sync flag to false every command, but that feels like 
>>>>>>>>>> overkill. I feel like there should be some a mechanism in GDB 
>>>>>>>>>> already that knows if we're the session leader or not, and 
>>>>>>>>>> thus handles things correctly, but I don't know what it is.
>>>>>>>>>>
>>>>>>>>>> Another possibility, based on the exact problem you had, is to 
>>>>>>>>>> put this at the end of either symbol expansions, or the 
>>>>>>>>>> reasons they are being expanded in the first place (which I 
>>>>>>>>>> suspect is something like trying to identify the language or 
>>>>>>>>>> name of the main function).
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> wait_sync_command_done() is not frequently called with command 
>>>>>>>>> execution.
>>>>>>>>> strace -k -o log ./gdb -p <<pid>>
>>>>>>>>> (gdb) ls
>>>>>>>>> Undefined command: "ls".  Try "help".
>>>>>>>>> (gdb) !ls
>>>>>>>>> (gdb) disassemble main
>>>>>>>>>
>>>>>>>>> confirmed the function wait_sync_command_done() is not part of 
>>>>>>>>> this trace. wait_sync_command_done() is called from 
>>>>>>>>> run_inferior_call()
>>>>>>>>> and serve as inferior startup and wait for it to stop.
>>>>>>>>>
>>>>>>>>> /* Subroutine of call_function_by_hand to simplify it.
>>>>>>>>>     Start up the inferior and wait for it to stop.
>>>>>>>>>     Return the exception if there's an error, or an exception with
>>>>>>>>>     reason >= 0 if there's no error.
>>>>>>>>>
>>>>>>>>>     This is done inside a TRY_CATCH so the caller needn't worry 
>>>>>>>>> about
>>>>>>>>>     thrown errors.  The caller should rethrow if there's an 
>>>>>>>>> error.  */
>>>>>>>>>
>>>>>>>>> static struct gdb_exception
>>>>>>>>> run_inferior_call (std::unique_ptr<call_thread_fsm> sm,
>>>>>>>>>                     struct thread_info *call_thread, CORE_ADDR 
>>>>>>>>> real_pc)
>>>>>>>>> {
>>>>>>>>>
>>>>>>>>>        /* Inferior function calls are always synchronous, even 
>>>>>>>>> if the
>>>>>>>>>           target supports asynchronous execution. */
>>>>>>>>>        wait_sync_command_done ();
>>>>>>>>>
>>>>>>>>> So wait_sync_command_done called once per inferior at startup.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Hi Guinevere,
>>>>>>>>>
>>>>>>>>> Thanks for the review and sorry for the delay in reply.
>>>>>>>>> Please find comments inline.
>>>>>>>>>
>>>>>>>>> I will send the V2 incorporating rest of the comment.
>>>>>>>>>
>>>>>>>>> Thanks
>>>>>>>>> Partha
>>>>>>>>
>>>>>>> Hi! Thanks for the updated version. It looks much better!
>>>>>>>
>>>>>>> However, I still cant apply the patch. Are you sure you're 
>>>>>>> developing on the master branch of our upstream repository? 
>>>>>>> (https://urldefense.com/v3/__https://sourceware.org/git/binutils-gdb.git__;!!ACWV5N9M2RV99hQ!N_X8-tLG80n66yoOg95U0435CrvbbnDiHbebshHmNxivPGKLL5ZTy2le27VURzCGpKU6zzBqP4Jtu3d5km1jRA$ )
>>>>>>>
>>>>>>> I have been manually changing the source code to test the patch, 
>>>>>>> but it should cleanly apply for other maintainer to have an 
>>>>>>> easier time reviewing things.
>>>>>>>
>>>>>>>>
>>>>>>>> Problem: While gdb is attaching an inferior, if ctrl-c is 
>>>>>>>> pressed in the
>>>>>>>> middle of the process attach,  the sigint is passed to the debugged
>>>>>>>> process. This triggers the exit of the inferior. For example in 
>>>>>>>> pstack,
>>>>>>>> printing a stack can take significant time, and ctrl-c is 
>>>>>>>> pressed to
>>>>>>>> abort the pstack/gdb application. This in turn kills the debugged
>>>>>>>> process, which can be critical for the system. In this case, the
>>>>>>>> intention of ctrl+c is to kill pstack/gdb, but not the inferior
>>>>>>>> application.
>>>>>>>> gdb -p <<pid>>
>>>>>>>> or gdb /proc/<<pid>>/exe pid
>>>>>>>> Attaching to process
>>>>>>>> << ctrl+c is pressed during attach
>>>>>>>> (gdb) q
>>>>>>>> <<<< inferior process exited >>>>
>>>>>>>>
>>>>>>>> A Ctrl-C/sigint received by gdb during the attachment of an 
>>>>>>>> inferior
>>>>>>>> passed to the debugged at some definite points during the window of
>>>>>>>> process attachment. The process of attaching an inferior is a 
>>>>>>>> multistep
>>>>>>>> process, and it takes time to get ready with the GDB prompt. As the
>>>>>>>> debugger and debugger are not fully attached during this period, 
>>>>>>>> the
>>>>>>>> sigint takes its default action to terminate the process.
>>>>>>>>
>>>>>>>> Solution: While GDB attaches processes, the inferior is not the 
>>>>>>>> current
>>>>>>>> session leader. Hence, until attach is complete and the GDB 
>>>>>>>> prompt is
>>>>>>>> available, the sigint should not be passed to the inferior.
>>>>>>>> The signal should be skipped if the process runs in the 
>>>>>>>> background. With
>>>>>>>> this approach, we can skip passing the signature if the process is
>>>>>>>> attached to the GDB and the process attach is not complete.
>>>>>>>> ---
>>>>>>>>  gdb/inferior.h | 3 +++
>>>>>>>>  gdb/target.c   | 4 ++++
>>>>>>>>  gdb/top.c      | 2 ++
>>>>>>>>  3 files changed, 9 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/gdb/inferior.h b/gdb/inferior.h
>>>>>>>> index 4d001b0ad50e..d5d01bd0d09c 100644
>>>>>>>> --- a/gdb/inferior.h
>>>>>>>> +++ b/gdb/inferior.h
>>>>>>>> @@ -557,6 +557,9 @@ class inferior : public refcounted_object,
>>>>>>>>    /* True if this child process was attached rather than 
>>>>>>>> forked. */
>>>>>>>>    bool attach_flag = false;
>>>>>>>>
>>>>>>>> +  /* True if inferior has been fully synced and prompt is no 
>>>>>>>> longer blocked.  */
>>>>>>>> +  bool sync_flag = false;
>>>>>>>> +
>>>>>>>>    /* If this inferior is a vfork child, then this is the 
>>>>>>>> pointer to
>>>>>>>>       its vfork parent, if GDB is still attached to it.  */
>>>>>>>>    inferior *vfork_parent = NULL;
>>>>>>>> diff --git a/gdb/target.c b/gdb/target.c
>>>>>>>> index d5bfd7d0849b..4eff3130bad7 100644
>>>>>>>> --- a/gdb/target.c
>>>>>>>> +++ b/gdb/target.c
>>>>>>>> @@ -3826,6 +3826,10 @@ struct target_ops *
>>>>>>>>                  through the target_stack.  */
>>>>>>>>               scoped_restore_current_inferior restore_inferior;
>>>>>>>>               set_current_inferior (inf);
>>>>>>>> +             if ((current_inferior ()->attach_flag)
>>>>>>>> +                 && !(current_inferior ()->sync_flag))
>>>>>>>> +                   return;
>>>>>>> also, there's still 8 spaces here. All 8 space-identations should 
>>>>>>> be replaced with tabs.
>>>>>>>> +
>>>>>>>>               current_inferior ()->top_target ()->pass_ctrlc ();
>>>>>>>>               return;
>>>>>>>>             }
>>>>>>>> diff --git a/gdb/top.c b/gdb/top.c
>>>>>>>> index a685dbf5122e..f05fdd161a42 100644
>>>>>>>> --- a/gdb/top.c
>>>>>>>> +++ b/gdb/top.c
>>>>>>>> @@ -542,6 +542,8 @@ struct ui_out **
>>>>>>>>    while (gdb_do_one_event () >= 0)
>>>>>>>>      if (ui->prompt_state != PROMPT_BLOCKED)
>>>>>>>>        break;
>>>>>>>> +
>>>>>>>> +  current_inferior ()->sync_flag = true;
>>>>>>>
>>>>>>> I'm still not 100% convinced this is the best place to put this. 
>>>>>>> Mainly because this function is also called by 
>>>>>>> maybe_wait_sync_command_done; it didn't show up in your testing 
>>>>>>> because when we run gdb from a terminal, the UI is synchronous 
>>>>>>> (so it fails the first part of the IF condition), but this would 
>>>>>>> be exercised in other situations. And 
>>>>>>> maybe_wait_sync_command_done is called after every single command.
>>>>>>>
>>>>>>> I tried adding this to setup_inferior, which looked like the 
>>>>>>> perfect place for it, but it unfortunately didn't work. Since 
>>>>>>> done is better than perfect, I'm not going to block this patch on 
>>>>>>> this, but I'd love to see a more logical place for this code.
>>>>>>>
>>>>>>
>>>>>> Hi Guinevere,
>>>>>>
>>>>>> Can't agree more on setup_inferior is the best place to reset this 
>>>>>> variable. Updated V3 of review accordingly. Added a 
>>>>>> check_quit_flag which will clear quit_flag, if set before 
>>>>>> setup_inferior.
>>>>>>
>>>>>>
>>>>>> Author: Partha Sarathi Satapathy <partha.satapathy@oracle.com>
>>>>>> Date:   Fri Nov 17 11:42:11 2023 +0000
>>>>>>
>>>>>> gdb : Signal to pstack/gdb kills the attached process.
>>>>>>
>>>>>> Problem: While gdb is attaching an inferior, if ctrl-c is pressed 
>>>>>> in the
>>>>>> middle of the process attach,  the sigint is passed to the debugged
>>>>>> process. This triggers the exit of the inferior. For example in 
>>>>>> pstack,
>>>>>> printing a stack can take significant time, and ctrl-c is pressed to
>>>>>> abort the pstack/gdb application. This in turn kills the debugged
>>>>>> process, which can be critical for the system. In this case, the
>>>>>> intention of ctrl+c is to kill pstack/gdb, but not the inferior
>>>>>> application.
>>>>>> gdb -p <<pid>>
>>>>>> or gdb /proc/<<pid>>/exe pid
>>>>>> Attaching to process
>>>>>> << ctrl+c is pressed during attach
>>>>>> (gdb) q
>>>>>> <<<< inferior process exited >>>>
>>>>>>
>>>>>> A Ctrl-C/sigint received by gdb during the attachment of an inferior
>>>>>> passed to the debugged at some definite points during the window of
>>>>>> process attachment. The process of attaching an inferior is a 
>>>>>> multistep
>>>>>> process, and it takes time to get ready with the GDB prompt. As the
>>>>>> debugger and debugger are not fully attached during this period, the
>>>>>> sigint takes its default action to terminate the process.
>>>>>>
>>>>>> Solution: While GDB attaches processes, the inferior is not the 
>>>>>> current
>>>>>> session leader. Hence, until attach is complete and the GDB prompt is
>>>>>> available, the sigint should not be passed to the inferior.
>>>>>> The signal should be skipped if the process runs in the 
>>>>>> background. With
>>>>>> this approach, we can skip passing the signature if the process is
>>>>>> attached to the GDB and the process attach is not complete.
>>>>>
>>>>> Hi!
>>>>>
>>>>> Sorry about the delay on this. I think this is patch looks good to 
>>>>> me, Reviewed-By: Guinevere Larsen <blarsen@redhat.com>
>>>>>
>>>>> I hope some maintainer for this area look at this soon!
>>>>>
>>>>
>>>> Hi Team,
>>>>
>>>> Great if we can get a update on further proceedings on this.
>>>>
>>>> Thanks
>>>> Partha
>>>
>>> Hi Guinevere and Team,
>>>
>>> Great if we can have further update on this.
>>> One more thing notice the online thread for this issue:
>>> https://urldefense.com/v3/__https://sourceware.org/pipermail/gdb-patches/2023-November/204251.html__;!!ACWV5N9M2RV99hQ!IQdn9yPks2xKcRBSz9b4tX70VzdhNoeJeDSZcP_19T3lqehiY8L3kI4fu0TrxTl30v7JqxkkW_XHAA77K1CGhg$ is missing last couple of communications.
>>>
>>> Thanks
>>> Partha
>>
>> Hi Team,
>>
>> Can you please help with further proceedings on this.
>>
>> Thanks
>> Partha
>>
> Hi Partha! I'm sorry this is taking so long. I would suggest that you 
> rebase your patch on the master branch and send a version 4 which is 
> just the rebase to ping this. You also don't need to keep our previous 
> comments on the v4 email, since folks will be able to see this history, 
> and that will make it easier for maintainers to review your code
> 
> If you do send a v4, remember to add my review tag to the end of the 
> commit message :)
> 
> I hope this gets an approval soon.
> 

Author: Partha Sarathi Satapathy <partha.satapathy@oracle.com>
Date:   Fri Nov 17 09:18:56 2023 +0000

gdb : Signal to pstack/gdb kills the attached process.

Problem: While gdb is attaching an inferior, if ctrl-c is pressed in the
middle of the process attach,  the sigint is passed to the debugged
process. This triggers the exit of the inferior. For example in pstack,
printing a stack can take significant time, and ctrl-c is pressed to
abort the pstack/gdb application. This in turn kills the debugged
process, which can be critical for the system. In this case, the
intention of ctrl+c is to kill pstack/gdb, but not the inferior
application.
gdb -p <<pid>>
or gdb /proc/<<pid>>/exe pid
Attaching to process
<< ctrl+c is pressed during attach
(gdb) q
<<<< inferior process exited >>>>

A Ctrl-C/sigint received by gdb during the attachment of an inferior
passed to the debugged at some definite points during the window of
process attachment. The process of attaching an inferior is a multistep
process, and it takes time to get ready with the GDB prompt. As the
debugger and debugger are not fully attached during this period, the
sigint takes its default action to terminate the process.

Solution: While GDB attaches processes, the inferior is not the current
session leader. Hence, until attach is complete and the GDB prompt is
available, the sigint should not be passed to the inferior.
The signal should be skipped if the process runs in the background. With
this approach, we can skip passing the signature if the process is
attached to the GDB and the process attach is not complete.

Reviewed-By: Guinevere Larsen <blarsen@redhat.com>
---
  gdb/infcmd.c   | 2 ++
  gdb/inferior.h | 3 +++
  gdb/target.c   | 3 +++
  3 files changed, 8 insertions(+)

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index c1fdbb300c67..8ab2d50477f4 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -2528,6 +2528,8 @@ enum async_reply_reason
    target_post_attach (inferior_ptid.pid ());

    post_create_inferior (from_tty);
+  current_inferior ()->sync_flag = true;
+  check_quit_flag();
  }

  /* What to do after the first program stops after attaching.  */
diff --git a/gdb/inferior.h b/gdb/inferior.h
index 7be28423aeb1..a6065da19a87 100644
--- a/gdb/inferior.h
+++ b/gdb/inferior.h
@@ -600,6 +600,9 @@ class inferior : public refcounted_object,
    /* True if this child process was attached rather than forked.  */
    bool attach_flag = false;

+  /* True if inferior has been fully synced and prompt is no longer 
blocked */
+  bool sync_flag = false;
+
    /* If this inferior is a vfork child, then this is the pointer to
       its vfork parent, if GDB is still attached to it.  */
    inferior *vfork_parent = NULL;
diff --git a/gdb/target.c b/gdb/target.c
index bbc1badc9e19..7c7df9c2ed87 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -3794,6 +3794,9 @@ struct target_ops *
                  through the target_stack.  */
               scoped_restore_current_inferior restore_inferior;
               set_current_inferior (inf);
+             if ((current_inferior ()->attach_flag)
+               && !(current_inferior ()->sync_flag))
+                 return;
               current_inferior ()->top_target ()->pass_ctrlc ();
               return;
             }
--
1.8.3.1


Hi Team,

Here is the V4 for review and its a rebase to latest.

Thanks
Partha