NetBSD Problem Report #54375

From gson@gson.org  Sun Jul 14 10:47:15 2019
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Date: Sun, 14 Jul 2019 13:47:09 +0300 (EEST)
From: gson@gson.org (Andreas Gustafsson)
Reply-To: gson@gson.org (Andreas Gustafsson)
To: gnats-bugs@NetBSD.org
Subject: gdb attached to running process shows extra thread
X-Send-Pr-Version: 3.95

>Number:         54375
>Category:       bin
>Synopsis:       gdb attached to running process shows extra thread
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    bin-bug-people
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jul 14 10:50:00 +0000 2019
>Closed-Date:    Mon Jul 15 13:00:14 +0000 2019
>Last-Modified:  Mon Jul 15 13:00:14 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        NetBSD-current, source date 2019.06.17.17.53.41
>Organization:

>Environment:
System: NetBSD
Architecture: x86_64
Machine: amd64
>Description:

When attaching gdb to a running threaded process, "info threads" shows
one of the threads twice, so that the total number of threads shown is
one more than the actual number.

>How-To-Repeat:

$ cat <<EOF >test.c
#include <unistd.h>
#include <pthread.h>
void *t(void *arg) {
  pause();
}
int main(int argc, char **argv) {
   pthread_t thread;
   pthread_create(&thread, 0, t, 0);
   pause();
}
EOF
$ cc test.c -lpthread -o test
$ ./test &
$ gdb ./test $!
(gdb) info threads

This shows three threads, even though the process has only two:

 Id   Target Id               Frame 
* 1    process 523 ""          0x000073b66be427da in _sys___sigsuspend14 () from /usr/lib/libc.so.12
  2    LWP 2 of process 523 "" 0x000073b66be427da in _sys___sigsuspend14 () from /usr/lib/libc.so.12
  3    LWP 1 of process 523 "" 0x000073b66be427da in _sys___sigsuspend14 () from /usr/lib/libc.so.12

If the program is started from within gdb instead of attaching to a
process already running, only two threads are shown:

$ gdb ./test
(gdb) run
^C
(gdb) info threads
  Id   Target Id               Frame 
  1    LWP 1 of process 979 "" 0x0000737a876427da in _sys___sigsuspend14 () from /usr/lib/libc.so.12
* 2    LWP 2 of process 979 "" 0x0000737a876427da in _sys___sigsuspend14 () from /usr/lib/libc.so.12

>Fix:

>Release-Note:

>Audit-Trail:
From: "Christos Zoulas" <christos@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/54375 CVS commit: src/external/gpl3/gdb/dist/gdb
Date: Sun, 14 Jul 2019 14:50:58 -0400

 Module Name:	src
 Committed By:	christos
 Date:		Sun Jul 14 18:50:58 UTC 2019

 Modified Files:
 	src/external/gpl3/gdb/dist/gdb: nbsd-nat.c

 Log Message:
 PR/54375: Andreas Gustafsson: gdb attached to running process shows extra
 thread. When attaching to a process that has threads make sure that we
 mutate the inferior_ptid (that currently has lwpid == 0 to the first thread
 we encounter.


 To generate a diff of this commit:
 cvs rdiff -u -r1.12 -r1.13 src/external/gpl3/gdb/dist/gdb/nbsd-nat.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

State-Changed-From-To: open->feedback
State-Changed-By: dholland@NetBSD.org
State-Changed-When: Sun, 14 Jul 2019 23:31:36 +0000
State-Changed-Why:
fixed?


State-Changed-From-To: feedback->closed
State-Changed-By: gson@NetBSD.org
State-Changed-When: Mon, 15 Jul 2019 13:00:14 +0000
State-Changed-Why:
Fixed, thanks!


>Unformatted:

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