Catégories: "Informatique"

A New Identi.ca/Twitter feed: Debian uploads

Avril 9th, 2013

After the Debian new packages, removal and bugs feeds (see the previous blog posts), I also plugged a feed with the last uploads in the archive:
Debian uploads on Identi.ca
Debian uploads on Twitter

As a reminder, here is the list.
For identi.ca:
Debian uploads
Debian NEW queue
Debian bugs
Debian removed packages

For Twitter:
Debian uploads
Debian NEW queue
Debian bugs
Debian removed packages

LLVM Debian/Ubuntu nightly packages

Avril 3rd, 2013

Lately, I have been working on providing nightly packages of the whole LLVM toolchain.
With the help of folks from Intel, Google and Apple, I am happy to announce the publication of these packages:
http://llvm.org/apt/

Built through a Jenkins instance (http://llvm-jenkins.debian.net/), packages for Debian wheezy and Unstable and Ubuntu quantal, precise and raring are created twice a day.

3.2 and 3.3 llvm-toolchain packages are currently waiting in the Debian NEW queue.

More information on the LLVM blog.

Rebuild of Debian using clang 3.2

Février 6th, 2013

After the studies of the rebuild of the Debian archive using clang 2.9 & 3.0 and 3.1, the results of the 3.2 rebuild have been published on http://clang.debian.net.

The percentage of failure is the same as clang 3.1: 12.1% of failure. That means that on 18264 packages, 2204 failed to be built with clang (it was 17710/2137 with the version 3.1).

The fact that the percentage is the same can be explained by at least two reasons:
First, some upstreams packages have been fixed to be built correctly with clang.
Second, the new warnings + -Werror (example: -Wsometimes-uninitialized) introduced in clang 3.2 triggered some new build failures.

To conclude, I think that the 3.2 release confirms the turning point of the 3.1. In term of support of the C and C++ standard, clang has now reached an equivalent quality to gcc (with better detection of errors and an extended set of warnings in -Wall).
Now, from the perspective of the Debian rebuilds, the decrease of number of failures will come from the upstream developers improving their codes (exemple of the error non-void function should return a value) or the Debian Developer/maintainer fixing the programming errors.

Some more cool stuff with LLVM/Clang

Janvier 12th, 2013

One of the drawback of C is the hard memory management.

It is because of this aspect that Clang provides a way to detect, at runtime, memory errors. Called Address Sanitizer, it allows, while the program is running, to keep track of the memory and detect typical errors (out-of-bound accesses, use of a variable after a free, etc).

# With the following packages (version 3.2-1~exp3)
$ sudo apt-get install clang clang-3.2 compiler-rt -t experimental

Taking the simple following example, even if the errors are obvious, compilers will accept this code.

#include <stdlib.h>
int main() {
    char *x = (char*)malloc(10 * sizeof(char*));
    free(x);
    return x[5];
}

Built and run with:

$ clang -O1 -g -fsanitize=address -fno-omit-frame-pointer foo.c -o foo
$ ./foo &> memoryDebug.log

The previous command will generate a log file. Log which can be post processed with the asan_symbolize command.

$ asan_symbolize memoryDebug.log

which will give:

=================================================================
==21368== ERROR: AddressSanitizer: heap-use-after-free on address 0x7fb22e547f45 at pc 0x408c44 bp 0x7ffff60c10b0 sp 0x7ffff60c10a8
READ of size 1 at 0x7fb22e547f45 thread T0
    #0 0x408c43 in main /tmp/foo.c:5
    #1 0x7fb22d99f6ac in __libc_start_main /home/adconrad/eglibc-2.16/csu/libc-start.c:227
0x7fb22e547f45 is located 5 bytes inside of 80-byte region [0x7fb22e547f40,0x7fb22e547f90)
freed by thread T0 here:
    #0 0x408c90 in __interceptor_free ??:0
    #1 0x408c0a in main /tmp/foo.c:4
    #2 0x7fb22d99f6ac in __libc_start_main /home/adconrad/eglibc-2.16/csu/libc-start.c:227
previously allocated by thread T0 here:
    #0 0x408d50 in __interceptor_malloc ??:0
    #1 0x408bff in main /tmp/foo.c:3
    #2 0x7fb22d99f6ac in __libc_start_main /home/adconrad/eglibc-2.16/csu/libc-start.c:227
Shadow byte and word:
  0x1ff645ca8fe8: fd
  0x1ff645ca8fe8: fd fd fd fd fd fd fd fd
More shadow bytes:
  0x1ff645ca8fc8: fa fa fa fa fa fa fa fa
  0x1ff645ca8fd0: fa fa fa fa fa fa fa fa
  0x1ff645ca8fd8: fa fa fa fa fa fa fa fa
  0x1ff645ca8fe0: fa fa fa fa fa fa fa fa
=>0x1ff645ca8fe8: fd fd fd fd fd fd fd fd
  0x1ff645ca8ff0: fd fd fd fd fd fd fd fd
  0x1ff645ca8ff8: fa fa fa fa fa fa fa fa
  0x1ff645ca9000: fa fa fa fa fa fa fa fa
  0x1ff645ca9008: fa fa fa fa fa fa fa fa
Stats: 0M malloced (0M for red zones) by 1 calls
Stats: 0M realloced by 0 calls
Stats: 0M freed by 1 calls
Stats: 0M really freed by 0 calls
Stats: 0M (128 full pages) mmaped in 1 calls
  mmaps   by size class: 8:2047;
  mallocs by size class: 8:1;
  frees   by size class: 8:1;
  rfrees  by size class:
Stats: malloc large: 0 small slow: 1
==21368== ABORTING

The main advantage compare to valgrind is that asan is supposed to be way more faster.

Threads can be also tricking to develop.
With the following example from stolen from upstream:

#include <pthread.h>
int Global;
void *Thread1(void *x) {
   Global = 42;
   return x;
}

int main() {
   pthread_t t;
   pthread_create(&t, NULL, Thread1, NULL);
   Global = 43;
   pthread_join(t, NULL);
   return Global;
}

$ clang -fsanitize=thread -g -O1 foo2.c -fPIE -pie -o foo
$ ./foo
==================
WARNING: ThreadSanitizer: data race (pid=21416)
  Write of size 4 at 0x7f2f1a214a50 by thread 1:
    #0 Thread1 /tmp/foo2.c:4 (exe+0x00000000f850)

  Previous write of size 4 at 0x7f2f1a214a50 by main thread:
    #0 main /tmp/foo2.c:10 (exe+0x00000000f8a4)

  Thread 1 (tid=21417, running) created at:
    #0 pthread_create ??:0 (exe+0x00000001267e)
    #1 main /tmp/foo2.c:9 (exe+0x00000000f894)

==================
ThreadSanitizer: reported 1 warnings

Note that clang also provides scan-build, a static analyzer for memory issues. Not as powerful as the Address Sanitizer (it only works on a file), it provides some excellent reports. See the Wouter's blog post on this subject or the automatic report of scan-build on Scilab.

Mini Debconf 2012 - videos and feedbacks

Décembre 12th, 2012

A bit more than two weeks after the Mini Debconf in Paris, I am glad to say that the videos of the event are finally published (the sound is not very good for the 4 first presentations, sorry about that).
They will be also available on the new IRILL website with a video player when ready.
All slides are also available on the page of the event.

I believe that there is a consensus about the quality of the event. We had around 150 people attending to the event, many interesting and various talks.
As usual, it was nice to meet some old and new friends from Debian.


Mini debconf - group picture
Group picture by Frederic Lehobey

For those who wonder, I am confident there will be a 2013 Parisian Mini Debconf.

Various feedbacks about the event:
Lucas Nussbaum
Stefano Zacchiroli
Vincent Untz
Raphael Hertzog
Pietro Abate
Logilab (Julien Cristau)
The 'official' Debian news

And, once more, many thanks to the sponsors!

Logilab

SmartJog

Bearstech

Evolix

IRILL