Tuesday 22 May 2018

rust for cortex-m7 baremetal

Update 14 December 2018: After the release of stable 1.31.0 (aka 2018 Edition), it is no longer necessary to switch to the nightly channel to get access to thumb7em-none-eabi / Cortex-M4 and Cortex-M7 components. Updated examples and commands accordingly.
For more details on embedded development using Rust, the official Rust embedded docs site is the place to go, in particular, you can start with The embedded Rust book.
This is a reminder for myself, if you want to install Rust for a baremetal Cortex-M7 target, this seems to be a tier 3 platform:


Higlighting the relevant part:

Target std rustc cargo notes
msp430-none-elf * 16-bit MSP430 microcontrollers
sparc64-unknown-netbsd NetBSD/sparc64
thumbv6m-none-eabi * Bare Cortex-M0, M0+, M1
thumbv7em-none-eabi *

Bare Cortex-M4, M7
thumbv7em-none-eabihf * Bare Cortex-M4F, M7F, FPU, hardfloat
thumbv7m-none-eabi * Bare Cortex-M3
x86_64-unknown-openbsd 64-bit OpenBSD

In order to enable the relevant support, use the nightly build and use stable >= 1.31.0 and add the relevant target:
eddy@feodora:~/usr/src/rust-uc$ rustup show
Default host: x86_64-unknown-linux-gnu

installed toolchains

nightly-x86_64-unknown-linux-gnu (default)

active toolchain

nightly-x86_64-unknown-linux-gnu (default)
rustc 1.28.0-nightly (cb20f68d0 2018-05-21)
eddy@feodora:~/usr/src/rust$ rustup show
Default host: x86_64-unknown-linux-gnu

stable-x86_64-unknown-linux-gnu (default)
rustc 1.31.0 (abe02cefd 2018-12-04)

If not using nightly, switch to that:

eddy@feodora:~/usr/src/rust-uc$ rustup default nightly-x86_64-unknown-linux-gnu
info: using existing install for 'nightly-x86_64-unknown-linux-gnu'
info: default toolchain set to 'nightly-x86_64-unknown-linux-gnu'

  nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.28.0-nightly (cb20f68d0 2018-05-21)
Add the needed target:
eddy@feodora:~/usr/src/rust$ rustup target add thumbv7em-none-eabi
info: downloading component 'rust-std' for 'thumbv7em-none-eabi'
info: installing component 'rust-std' for 'thumbv7em-none-eabi'
eddy@feodora:~/usr/src/rust$ rustup show
Default host: x86_64-unknown-linux-gnu

installed targets for active toolchain


active toolchain

stable-x86_64-unknown-linux-gnu (default)
rustc 1.31.0 (abe02cefd 2018-12-04)
Then compile with --target.

Thursday 10 May 2018

"Where does Unity store its launch bar items?" or "Convincing Ubuntu's Unity 7.4.5 to run the newer version of PyCharm when starting from the launcer"

I have been driving a System76 Oryx-Pro for some time now. And I am running Ubuntu 16.04 on it.
I typically try to avoid polluting global name spaces, so any apps I install from source I tend to install under a versioned directory under ~/opt, for instance, PyCharm Community Edition 2016.3.1 is installed under ~/opt/pycharm-community-2016.3.1.

Today, after Pycharm suggested I install a newer version, I downloaded the current package, and ran it, as instructed in the embedded readme.txt, via the wrapper script:
~/opt/pycharm-community-2018.1.2/bin$ ./pycharm.sh
Everything looked OK, but when wanting to lock the icon on the launch bar I realized Unity did not display a separate Pycharm Community Edition icon for the 2018.1.2 version, but showed the existing icon as active.

"I guess it's the same filename, so maybe unity confuses the older version with the new one, so I have to replace the launcher to user the newer version by default", I said.

So I closed the interface, then removed the PyCharm Community Edition, then I restarted the newer Pycharm from the command line, then blocked the icon, then I closed PyCharm once more, then clicked on the launcher bar.

Surprise! Unity was launching the old version! What?!

Repeated the entire series of steps, suspecting some PEBKAC, but was surprised to see the same result.

"Damn! Unity is stupid! I guess is a good thing they decided to kill it!", I said to myself.

Well, it shouldn't be that hard to find the offending item, so I started to grep in ~/.config, then in ~/.* for the string "PyCharm Cummunity Edition" without success.
Hmm, I guess the Linux world copied a lot of bad ideas from the windows world, probably the configs are not in ~/.* in plain text, they're probably in that simulacrum of a Windows registry called dconf, so I installed dconf-editor and searched once more for the keyword "Community", but only found one entry in the gedit filebrowser context.

So where does Unity gets its items from the launchbar? Since there is no "Properties" entry context menu and didn't want to try to debug the starting of my graphic environment, but Unity is open source, I had to look at the sources.

After some fighting with dead links to unity.ubuntu.com subpages, then searching for "git repository Ubuntu Unity", I realized Ubuntu loves Bazaar, so searched for "bzr Ubuntu Unity repository", no luck. Luckly, Wikipedia usually has those kind of links, and found the damn thing.

BTW, am I the only one considering some strong hits with a clue bat the developers which name projects by some generic term that has no chance to override the typical term in common parlance such as "Unity" or "Repo"?

Finding the sources and looking a little at the repository did not make it clear which was the entry point. I was expecting at least the README or the INSTALL file would give some relevant hints on the config or the initalization. M patience was running dry.

Maybe looking on my own system would be a better approach?
eddy@feodora:~$ which unity
eddy@feodora:~$ ll $(which unity)
-rwxr-xr-x 1 root root 9907 feb 21 21:38 /usr/bin/unity*
eddy@feodora:~$ ^ll^file
file $(which unity)
/usr/bin/unity: Python script, ASCII text executable
BINGO! This looks like a python script executable, it's not a binary, in spite of the many .cpp sources in the Unity tree.

I opened the file with less, then found this interesting bit:
 def reset_launcher_icons ():
    '''Reset the default launcher icon and restart it.'''
    subprocess.Popen(["gsettings", "reset" ,"com.canonical.Unity.Launcher" , "favorites"])
Great! So it stores that stuff in the pseudo-registry, but have to look under com.canonical.Unity.Launcher.favorites. Firing dconf-editor again found the relevant bit in the value of that key:
So where is this .desktop file? I guess using find is going to bring it up:
find /home/eddy/.local/ -name jetbrains* -exec vi {} \;
It did, and the content made it obvious what was happening:
[Desktop Entry]
Name=PyCharm Community Edition
Exec="/home/eddy/opt/pycharm-community-2016.3.1/bin/pycharm.sh" %f

Comment=The Drive to Develop
Probably Unity did not create a new desktop file when locking the icon, it would simply check if the jetbrains-pycharm-ce.desktop file existed already in my.local directory, saw it was, so it skipped its recreation.

Just as somebody said, all difficult computer science problems are eiether caused by leaky abstractions or caching. I guess here we're having some sort of caching issue, but is easy to fix, just edit the file:
eddy@feodora:~$ cat /home/eddy/.local/share/applications/jetbrains-pycharm-ce.desktop

[Desktop Entry]
Name=PyCharm Community Edition
Exec="/home/eddy/opt/pycharm-community-2018.1.2/bin/pycharm.sh" %f
Comment=The Drive to Develop
Checked again the start, and now the expected slash screen appears. GREAT!

I wonder if this is a Unity issue or is it due to some broken library that could affect other desktop environments such as MATE, GNOME or XFCE?

"Only" lost 2 hours (including this post) with this stupid bug, so I can go back to what I was trying in the first place, but now is already to late, so I have to go to sleep.

Friday 26 January 2018

Detecting binary files in the history of a git repository

Git, VCSes and binary files

Git is famous and has become popular even in the enterprise/commercial environments. But Git is also infamous regarding storage of large and/or binary files that change often, in spite of the fact they can be efficiently stored. For large files there have been several attempts to fix the issue, with varying degree of success, the most successful being git-lfs and git-annex.

My personal view is that, contrary to many practices, is a bad idea to store binaries in any VCS. Still, this practice has been and still is in use in may projects, especially in closed source projects. I won't go into the reasons, and how legitimate they are, let's say that we might finally convince people that binaries should be removed from the VCS, git, in particular.

Since the purpose of a VCS is to make sure all versions of the stored objects are never lost, Linus designed git in such a way that knowing the exact hash of the tip/head of your git branch, it is guaranteed the whole history of that branch hasn't changed even if the repository was stored in a non-trusted location (I will ignore hash collisions, for practical reasons).

The consequence of this is that if the history is changed one bit, all commit hashes and history after that change will change also. This is what people refer to when they say they rewrite the (git) history, most often, in the context of a rebase.

But did you know that you could use git rebase to traverse the history of a branch and do all sorts of operations such as detecting all binary files that were ever stored in the branch?

Detecting any binary files, only in the current commit

As with everything on *nix, we start with some building blocks, and construct our solution on top of them. Let's first find all files, except the ones in .git:

find . -type f -print | grep -v '^\.\/\.git\/'
Then we can use the 'file' utility to list for non-text files:
(find . -type f -print | grep -v '^\.\/\.git\/' | xargs file )| egrep -v '(ASCII|Unicode) text'
And if there are any such file, then it means the current git commit is one that needs our attention, otherwise, we're fine.
(find . -type f -print | grep -v '^\.\/\.git\/' | xargs file )| egrep -v '(ASCII|Unicode) text' && (echo 'ERROR:' && git show --oneline -s) || echo OK
 Of course, we assume here, the work tree is clean.

Checking all commits in a branch

Since we want to make this an efficient process and we only care if the history contains binaries, and branches are cheap in git, we can use a temporary branch that can be thrown away after our processing is finalized.
Making a new branch for some experiments is also a good idea to avoid losing the history, in case we do some stupid mistakes during our experiment.

Hence, we first create a new branch which points to the exact same tip the branch to be checked points to, and move to it:
git checkout -b test_bins
Git has many commands that facilitate automation, and my case I want to basically run the chain of commands on all commits. For this we can put our chain of commands in a script:

cat > ../check_file_text.sh

(find . -type f -print | grep -v '^\.\/\.git\/' | xargs file )| egrep -v '(ASCII|Unicode) text' && (echo 'ERROR:' && git show --oneline -s) || echo OK
then (ab)use 'git rebase' to execute that for us for all commits:
git rebase --exec="sh ../check_file_text.sh" -i $startcommit
After we execute this, the editor window will pop up, just save and exit. Assuming $startcommit is the hash of the first commit we know to be clean or beyond which we don't care to search for binaries, this will look in all commits since then.

Here is an example output when checking the newest 5 commits:

$ git rebase --exec="sh ../check_file_text.sh" -i HEAD~5
Executing: sh ../check_file_text.sh
Executing: sh ../check_file_text.sh
Executing: sh ../check_file_text.sh
Executing: sh ../check_file_text.sh
Executing: sh ../check_file_text.sh
Successfully rebased and updated refs/heads/test_bins.

Please note this process can change the history on the test_bins branch, but that is why we used a throw-away branch anyway, right? After we're done, we can go back to another branch and delete the test branch.

$ git co master
Switched to branch 'master'

Your branch is up-to-date with 'origin/master'
$ git branch -D test_bins
Deleted branch test_bins (was 6358b91).

Thursday 11 January 2018

Suppressing color output of the Google Repo tool

On Windows, in the cmd shell, the color control caracters generated by the Google Repo tool (or its windows port made by ESRLabs) or git appear as garbage. Unfortunately, the Google Repo tool, besides the fact it has a non-google-able name, lacks documentation regarding its options, so sometimes the only way to find out what is the option I want is to look in the code.
To avoid repeatedly look over the code to dig up this, future self, here is how you disable color output in the repo tool with the info subcommand:
repo --color=never info
Other options are 'auto' and 'always', but for some reason, auto does not do the right thing (tm) in Windows and garbage is shown with auto.