December/January (15/16) GNU Toolchain Update

[Nick Clifton <nickc at redhat dot com>]

Hi Guys,

  First of all I have an apology to make.  I managed to reformat my
  hard drive over the holidays, wiping away all of my notes for this
  blog.  In particular I was contacted by a reader about an
  enhancement to gcc's inline assembler support which I have now
  totally lost. :-(  So, dear reader, wherever you are, I apologise,
  and if you contact me again I will make sure that the extended asm
  enhancement gets mentioned in the next blog post.

  The big news, for me at least, is that binutils 2.26 is now out.
  This release contains lots of bug fixes of course, plus a few new
  features:

    *  A new configure option:
    
         --enable-compressed-debug-sections={all,gas,gold,ld,none}
	 
      which decides whether DWARF debug sections should be compressed
      by default.  By default this option is off for all of the tools,
      although of course it can be enabled via command line options.
      In future releases of binutils however, the option will be
      enabled by default.

    * Support for the ARC EM/HS and ARC600/700 architectures.

    * Support for the LLVM plugin.

    * Experimental support for linker garbage collection (--gc-sections)
      for COFF and PE based targets.

    * A new linker command line option:

        --orphan-handling=[place|warn|error|discard]

      is available which adjusts how orphan sections are handled.  The
      default is 'place' which gives the normal behaviour.  'warn' and
      'error' issue a warning or error respectively when an orphan
      section is found, and 'discard' will discard the section entirely.

     * The objcopy tool has a new option insert symbols into a file:
     
         --add-symbol <name>=[<section>:]<value>[,<flags>]

       It also has a new option to replace the contents of an existing
       section with the contents of a specified file:
       
          --update-section <section>=<filename>

     * In the assembler, symbol and label names can now be enclosed in
       double quotes (") which allows them to contain characters that
       are not part of valid symbol names in high level languages.

     * Support for the ARMv8.1 architecture has been added to the
       AArch64 and ARM ports.


  The next binutils release (2.27) should be happening in July of
  this year as the project attempts to move to a 6 month release
  schedule.

  In the development binutils there is now support for ARM NOREAD
  sections.  These are executable sections which contain code which
  the user is not allowed to see.


  Next - there is a new release of the Newlib C library.  Version
  2.3.0 contains several enhancements and improvements, including:

   - Dynamic atexit logic fixed.
   - ARM performance enhancements.
   - New version of strtold.
   - ARC platform support redone.
   - Strftime improvements/enhancements.
   - Complex math enhancements.
   - Visium platform support added.
   - OR1K platform support added.



  GCC meanwhile continues working on reducing bug numbers so that a
  version 6 branch can be created.  In practice this means that new
  features are not being added to the sources at this point, although
  there is one new warning option to report:
  
    -Winvalid-memory-model

  This warns for invocations of__atomic Builtins, __sync Builtins, and
  the C11 atomic generic functions with a memory consistency argument
  that is either invalid for the operation or outside the range of
  values of the memory_order enumeration.  For example, since the
  __atomic_store and __atomic_store_n built-ins are only defined for
  the relaxed, release, and sequentially consistent memory orders the
  following code will produce a warning: 

     void store (int *i)
     {
       __atomic_store_n (i, 0, memory_order_consume);
     }

  This option is enabled by default.

  The development version of GCC also no longer supports DWARF Version
  1, which is substantially different than Version 2 and later.  For
  historical reasons, some other DWARF-related options (including
  -feliminate-dwarf2-dups and -fno-dwarf2-cfi-asm) retain a reference
  to DWARF Version 2 in their names, but apply to all
  currently-supported versions of DWARF. 


  The GDB debugger continues to improve as well, and in the last
  couple of months these new features have been added to the
  development version:

    * Support for debugging kernel-based threads on FreeBSD.

    * Thread numbers are now per inferior instead of global.  If
      you are debugging multiple inferiors, GDB displays thread IDs
      using a qualified INF_NUM.THR_NUM form.  For example:

     (gdb) info threads
       Id   Target Id         Frame
       1.1  Thread 0x7ffff7fc2740 (LWP 8155) (running)
       1.2  Thread 0x7ffff7fc1700 (LWP 8168) (running)
     * 2.1  Thread 0x7ffff7fc2740 (LWP 8157) (running)
       2.2  Thread 0x7ffff7fc1700 (LWP 8190) (running)

     As consequence, thread numbers as visible in the $_thread
     convenience variable and in Python's InferiorThread.num attribute
     are no longer unique between inferiors.

     GDB now maintains a second thread ID per thread, referred to as
     the global thread ID, which is the new equivalent of thread
     numbers in previous releases.  See also $_gthread below.

     For backwards compatibility, MI's thread IDs always refer to
     global IDs.

     Commands that accept thread IDs now accept the qualified
     INF_NUM.THR_NUM form as well.  For example:

       (gdb) thread 2.1
       [Switching to thread 2.1 (Thread 0x7ffff7fc2740 (LWP 8157))] (running)
       (gdb)

     In commands that accept a list of thread IDs, you can now refer
     to all threads of an inferior using a star wildcard.  GDB accepts
     "INF_NUM.*", to refer to all threads of inferior INF_NUM, and "*"
     to refer to all threads of the current inferior.  For example,
     "info threads 2.*".

     You can use "info threads -gid" to display the global thread ID
     of all threads.

     The new convenience variable $_gthread holds the global number of
     the current thread, and $_inferior holds the number of the
     current inferior.

  * GDB now displays the ID and name of the thread that hit a breakpoint
    or received a signal, if your program is multi-threaded.  For
    example:

      Thread 3 "bar" hit Breakpoint 1 at 0x40087a: file program.c, line 20.
      Thread 1 "main" received signal SIGINT, Interrupt.

That's all for now.  More again in a couple of month's time.

Cheers
  Nick