[binutils-gdb] gdb: Fix instability in thread groups test

[Andrew Burgess]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=67943c005fafa4397535766787b4fbda338ac07d

commit 67943c005fafa4397535766787b4fbda338ac07d
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Fri Aug 10 10:16:32 2018 +0100

    gdb: Fix instability in thread groups test
    
    In the test script gdb.mi/list-thread-groups-available.exp we ask GDB
    to list all thread groups, and match the output against a
    regexp. Occasionally, I would see this test fail.
    
    The expected output is a list of entries, each entry looking roughly
    like this:
    
      {id="<DECIMAL>",type="process",description="<STRING>",
       user="<STRING>",cores=["<DECIMAL>","<DECIMAL>",...]}
    
    All the fields after 'id' and 'type' are optional, and the 'cores'
    list can contain 1 or more "<DECIMAL>" entries.
    
    On my machine (Running Fedora 27, kernel 4.17.3-100.fc27.x86_64)
    usually the 'description' is a non-empty string, and the 'cores' list
    has at least one entry in it.  But sometimes, very rarely, I'll see an
    entry in the process group list where the 'description' is an empty
    string, the 'user' is the string "?", and the 'cores' list is empty.
    Such an entry looks like this:
    
       {id="19863",type="process",description="",user="?",cores=[]}
    
    I believe that this is caused by the process exiting while GDB is
    scanning /proc for process information.  The current code in
    gdb/nat/linux-osdata.c is not (I think) resilient against exiting
    processes.
    
    This commit adjusts the regex that matches the 'cores' list so that an
    empty list is acceptable, with this patch in place the test script
    gdb.mi/list-thread-groups-available.exp never fails for me now.
    
    I've only adjusted the cores regexp for the occasion when we have GDB
    read information about all processes, its only in this case that we
    might encounter an exiting process.  When we read information about
    two known PIDs, that we know will not exit for the duration of the
    test, we require that the core list be non-empty.
    
    gdb/testsuite/ChangeLog:
    
    	* gdb.mi/list-thread-groups-available.exp: Update test regexp.

Diff:
---
 gdb/testsuite/ChangeLog                               |  4 ++++
 gdb/testsuite/gdb.mi/list-thread-groups-available.exp | 12 +++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index bd3c3bf..33749aa 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2018-08-14  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.mi/list-thread-groups-available.exp: Update test regexp.
+
 2018-08-09  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb.base/vla-optimized-out.exp: Add new test.
diff --git a/gdb/testsuite/gdb.mi/list-thread-groups-available.exp b/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
index c4dab2a..34066a8 100644
--- a/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
+++ b/gdb/testsuite/gdb.mi/list-thread-groups-available.exp
@@ -45,7 +45,11 @@ set id_re "id=\"$decimal\""
 set type_re "type=\"process\""
 set description_re "description=\"$string_re\""
 set user_re "user=\"$string_re\""
-set cores_re "cores=\\\[\"$decimal\"(,\"$decimal\")*\\\]"
+
+# The CORES_RE regexp allows a process to be running on zero or more
+# cores.  The former can happen if a process exits while GDB is
+# reading information out of /proc.
+set cores_re "cores=\\\[(\"$decimal\"(,\"$decimal\")*)?\\\]"
 
 # List all available processes.
 set process_entry_re "{${id_re},${type_re}(,$description_re)?(,$user_re)?(,$cores_re)?}"
@@ -64,6 +68,12 @@ set spawn_id_2 [remote_spawn target $binfile]
 set pid_2 [spawn_id_get_pid $spawn_id_2]
 set id_re_2 "id=\"$pid_2\""
 
+# Unlike the earlier CORES_RE this list must contain at least one
+# core.  Given that we know these processes will not exit while GDB is
+# reading their information from /proc we can expect at least one core
+# for each process.
+set cores_re "cores=\\\[\"$decimal\"(,\"$decimal\")*\\\]"
+
 set process_entry_re_1 "{${id_re_1},${type_re}(,$description_re)?(,$user_re)?(,$cores_re)?}"
 set process_entry_re_2 "{${id_re_2},${type_re}(,$description_re)?(,$user_re)?(,$cores_re)?}"