Provide gdb helper script to ease debugging #20

wilson6405 · 2020-01-31T13:28:16Z

When qtest stopped by debugger during the tracing, it would over
time_limit seconds and trigger timeout exception.

Signed-off-by: Kickasson face.ateam0902@gmail.com

jserv · 2020-01-31T14:02:00Z

I would like to defer to @afcidk .

Makefile

jserv · 2020-02-01T04:04:03Z

Instead of providing conditional builds, how about consolidating them by extra runtime option --debug which would suppress exception handling?
Reference: https://www.mono-project.com/docs/debug+profile/debug/

wilson6405 · 2020-02-01T08:40:51Z

Sounds great. I am going to read this article later.
Under the suppressing exception handling I have two ideas:

Active: trigger gdb shell and attach qtest which is received signal SIGSEGV
Passive: use extra run-time option -d during gdb debugging

In my experience, optimizations that do interfere with debugging without -Og.

jserv · 2020-02-07T02:57:07Z

Any change for further work?

wilson6405 · 2020-02-08T13:19:28Z

Sorry for the delay.
Should I update this PR or create a new one?

jserv · 2020-02-08T13:39:42Z

Sorry for the delay.
Should I update this PR or create a new one?

You can force push revised commits.

jserv · 2020-02-10T12:47:38Z

qtest.c

+            "pointer");
+        char cmd[1024] = {0};
+        snprintf(cmd, sizeof(cmd), "gdb -q -p %d -ex bt", getpid());
+        if (system(cmd) != 0) {


Don't use system(), which might lead to unexpected execution flow. Instead, use posix_spawn(3) for fine-grained control over external process(es).

wilson6405 · 2020-02-10T15:05:28Z

Should I replace -O1 with -Og?

jserv · 2020-02-10T15:28:32Z

Should I replace -O1 with -Og?

I expect such build-specific changes should take place in another pull request.

jserv · 2020-02-10T15:34:27Z

qtest.c

+        char cmd[64] = {0};
+        snprintf(cmd, sizeof(cmd), "gdb -q -p %d -ex bt", getpid());
+        char *argv[] = {"sh", "-c", cmd, NULL};
+        if ((ret = posix_spawn(&pid, "/bin/sh", NULL, NULL, argv, environ)) == 0) {


@afcidk, Please take a look over the implementation. I am not sure if we shall raise signals when it takes much longer time to launch GDB than usual.

We should avoid launching GDB within qtest. Instead, we can prepare specific GDB scripts which deal with certain signals and/or process flow.

I agree with that. We could use handle SIGALRM ignore to deal with SIGALRM or other signals.

Or we could provide an option to enable qtest to crash manually by adding functions such as abort() in sigsegvhandler to generate the core file for further analysis.

wilson6405 · 2020-02-19T15:50:10Z

To sum up, create a script which contain two features:

Setup handle SIGALRM ignore first and run qtest in gdb shell.
Analyze core-dump file

About core-dump file, do we need to change /proc/sys/kernel/core_pattern? Because it needs permission.

jserv · 2020-02-20T00:37:03Z

As for /proc/sys/kernel/core_pattern, you can detect and assist users to configure kernel via sysctl or procfs accordingly.

jserv · 2020-02-21T02:23:47Z

Please rebase the latest master branch

wilson6405 · 2020-02-21T14:22:11Z

Oh, I forget to rebase the local branch.

jserv · 2020-02-21T15:45:10Z

You shall update documentation in top-level README.md.

jserv · 2020-02-22T05:36:46Z

README.md

 * Makefile : Builds the evaluation program `qtest`
 * README.md : This file
 * scripts/driver.py : The driver program, runs `qtest` on a standard set of traces
+* scripts/debug.py : The debug program, debug `qtest` without interruption by **SIGALRM** or analyze core-dump which is generated by `qtest`


Change the description to

The helper program for GDB, executes qtest without SIGALRM and/or analyzes generated core dump file.

Append a new section about debugging facilities.

qtest.c

jserv · 2020-02-22T05:40:16Z

File .gitignore should be updated to include core.

jserv · 2020-02-23T09:51:37Z

README.md

+```
+* Enter GDB without interruption by **SIGALRM**
+```
+$ ./debug --d


Why was debug located here?

jserv · 2020-02-23T09:52:09Z

README.md

  * XX is the trace number (1-15).  CAT describes the general nature of the test.
 * traces/trace-eg.cmd : A simple, documented trace file to demonstrate the operation of `qtest`

+## Usage of debug.py


Change the section name to "Debugging Facilities"

jserv · 2020-02-23T09:52:47Z

README.md

+This script provides two options for dedugging
+```
+  -d, --debug    Enter gdb shell
+  -a, --analyze  Analyze the core-dump file


We usually say "core dump file" or "core dump" without dashes.

jserv · 2020-02-23T09:53:19Z

scripts/debug.py

@@ -0,0 +1,83 @@
+#!/usr/bin/python3


Change it to #!/usr/bin/env python3.

jserv · 2020-02-23T12:42:15Z

README.md

+
+This script provides two options for debugging.
+```
+$ ./debug.py -h


Should be $ scripts/debug.py

jserv · 2020-02-23T12:43:06Z

README.md

 * Makefile : Builds the evaluation program `qtest`
 * README.md : This file
 * scripts/driver.py : The driver program, runs `qtest` on a standard set of traces
+* scripts/debug.py : The helper program for GDB, executes qtest without SIGALRM and/or analyzes generated core dump file. For more detial: [Debugging Facilities](#Debugging-Facilities)


You don't have to mention its detailed usage since this section is a listing for files.

jserv · 2020-02-23T12:43:59Z

README.md

+  The core dump file was created in the working directory of the `qtest`.
+  * Allow the core dumps by using shell built-in command **ulimit**.
+  ```
+  $ ulimit -c unlimited // Set core file size 


Don't mix C++-style comments within shell commands.

1. Setup handle SIGALRM ignore first and run qtest in gdb shell 2. Analyze core dump file

jserv · 2020-02-23T13:24:54Z

README.md

+Starting program: lab0-c/qtest 
+cmd> 
+```
+* It's handy to analyze the core dump file.


You shall emphasize on the features and motivations regarding analysis on core dump as well.

jserv · 2020-02-24T12:54:10Z

README.md


+## Debugging Facilities
+
+This script provides two options for debugging.


Again, summarize the motivations of the GDB helper program in this section.

Add "Debugging Facilities" section to README.md

jserv · 2020-02-25T23:11:55Z

Thank @wilson6405 for contributing!

afcidk suggested changes Jan 31, 2020

View reviewed changes

Makefile Outdated Show resolved Hide resolved

Makefile Show resolved Hide resolved

wilson6405 force-pushed the pull-request branch from f72d3c7 to 5008d53 Compare February 10, 2020 12:16

jserv reviewed Feb 10, 2020

View reviewed changes

wilson6405 force-pushed the pull-request branch from 5008d53 to 5a52173 Compare February 10, 2020 15:01

jserv reviewed Feb 10, 2020

View reviewed changes

wilson6405 force-pushed the pull-request branch from 5a52173 to 454b7fb Compare February 20, 2020 16:00

wilson6405 force-pushed the pull-request branch from 454b7fb to 040adbb Compare February 21, 2020 14:20

wilson6405 force-pushed the pull-request branch 2 times, most recently from a1e6a1d to 83122a6 Compare February 21, 2020 14:58

jserv requested a review from afcidk February 21, 2020 15:45

jserv reviewed Feb 22, 2020

View reviewed changes

qtest.c Show resolved Hide resolved

wilson6405 force-pushed the pull-request branch 2 times, most recently from 5be9ead to 599aef8 Compare February 23, 2020 07:13