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Summer 2017 GNU Toolchain Update


Hi Guys,

  It has been a long time since my last post on the developments in
  the toolchain, so there is lots to report:

-------------------------------------------------------------------
Binutils:

  Version 2.29 has been released.

  In addition to previous changes already detailed in this blog, this
  release also contains:

    * Support for placing sections into special memory areas on
      systems that use virtual memory managers.  This is like the
      MEMORY command in linker scripts except that that only works
      on systems without a memory management unit.

      With the new system sections can be marked as requiring a
      particular kind of special memory.  The linker collects together
      all of the sections with the same requirements and places them
      into a specially marked segment.  The loader can then detect
      this segment's requirements and ensure that the right kind of
      memory is used.

    * Support for the WebAssembly file format and conversion to the
      wasm32 ELF format.

    * The PowerPC assembler now checks that the correct register class
      is used in instructions.

    * The ARM assemblers now support the ARMv8-R architecture and
      Cortex-R52 processors.

    * The linker now supports ELF GNU program properties.  These are
      run-time notes intended for the loader that tell it more about
      the binary that it is initializing.

    * The linker contains support for Intel's Indirect Branch Tracking
      (IBT) enhancement.  This is a technology intended to help fight
      malicious code that abuses the stack to force unwanted behaviour
      from a program.  For more information see:
      
https://software.intel.com/sites/default/files/managed/4d/2a/control-flow-enforcement-technology-preview.pdf

    * Section groups can now be resolved (the group deleted and the
      group members placed like normal sections) at partial link time
      either using the new linker option --force-group-allocation or
      by placing FORCE_GROUP_ALLOCATION into the linker script.
      
    * The MIPS port now supports:
    
        + MicroMIPS eXtended Physical Addressing (XPA) instructions.
	+ Release 5 of the ISA.
        + Imagination interAptiv MR2 processor.
        + MIPS16e2 ASE for assembly and disassembly.

    * The SPARC port now supports the SPARC M8 processor, which
      implements the Oracle SPARC Architecture 2017.

    * Objdump's --line-numbers option can now be augmented via the new
      --inlines option so that inlined functions will display their
      nesting information. 

    * Objcopy now has an option '--merge-notes' to reduce the size of
      notes in a binary file by merging and deleting redundant entries. 

    * The AVR assembler has support for the __gcc_isr
      pseudo-instruction.  This instruction is generated by GCC when
      it wants to create the prologue or epilogue of an interrupt
      handler.  The assembler then ensures that the most optimal code
      possible is generated.

  Meanwhile in the mainline binutils sources:

  * The assembler now has support for location views in DWARF debug
    line information.  This is part of a project to help improve the
    source code location information that the compiler provides to the
    debugger:

https://developers.redhat.com/blog/2017/07/11/statement-frontier-notes-and-location-views/#more-437095

------------------------------------------------------------------------
GDB

  Version 8.0 has been released.  This release contains:

    * Support for C++ rvalue references.

    * Python scripting enhancements:
      + New functions to start, stop and access a running btrace
        recording.
      + Rvalue reference support in gdb.Type.

    * GDB commands interpreter:
      + User commands now accept an unlimited number of arguments.
      + The "eval" command now expands user-defined arguments.

    * DWARF version 5 support

    * GDB/MI enhancements:
      + New -file-list-shared-libraries command to list the shared
        libraries in the program. 
      + New -target-flash-erase command, to erase flash memory.

    * Support for native FreeBSD/mips (mips*-*-freebsd)

    * Support for the Synopsys ARC and FreeBSD/mips targets.

  For a complete list and more details on each item, please see the
  gdb/NEWS file in the release sources.

  Meanwhile in the development sources the following new features have
  been added:

    * On Unix systems, GDBserver now does globbing expansion and
      variable substitution in inferior command line arguments.

    * New commands  
      + set debug separate-debug-file
      + show debug separate-debug-file
      These control the display of debug output about separate debug
      file search.

----------------------------------------------------------------------
GCC

  Version 7.1 has been released.  Most of the enhancements and new
  features in this release have already been reported in earlier
  versions of this blog, but there are a couple of new things that
  made it in before the deadline:

    * A new loop splitting optimization pass has been added.  Certain
      loops which contain a condition that is always true on one side
      of the iteration space and always false on the other are split
      into two loops, such that each of the two new loops iterates on
      just one side of the iteration space and the condition does not
      need to be checked inside of the loop. 

    * The PowerPC port's support for ISA 3.0 has been enhanced to
      generate more of the new instructions by default, and to provide
      more built-in functions to generate code for the other new
      instructions.

  Meanwhile in the developement sources:

    * Support for the SPARC M8 processor has been added.

    * The switches '-mfix-ut700' and '-mfix-gr712rc' options have been
      added to work around an erratum in LEON3FT SPARC processors.

    * Several new warning options have been added as well:
    
      + The option '-Wmultistatement-macros' warns about unsafe
        multiple statement macros that appear to be guarded by a
        clause in which only the first statement is actually
        protected.  For example:

            #define DOIT x++; y++
            if (c) DOIT;

      + The option '-Wsizeof-pointer-div' warns about suspicious
        divisions of two sizeof expressions that divide a pointer size
        by an element size, when the object concerned is a pointer not
	an array.  For example:

          char *ptr;
	  int a = sizeof (ptr) / sizeof (ptr[0]);
-----------------------------------------------------------------------
GLIBC

  Work on version 2.26 continues.  New features that have been added
  include:

    * A per-thread cache has been added to malloc.  Access to the
      cache requires no locks and therefore significantly accelerates
      the fast path to allocate and free small amounts of memory.
      Refilling an empty cache requires locking the underlying arena,
      but the performance improvements are still significant.

    * Unicode 10.0.0 Support: Character encoding, character type info,
      and transliteration tables are all updated to the Unicode 10.0.0
      standard.

    * Improvements to the DNS stub resolver:

      + The GNU C Library will now detect when /etc/resolv.conf has
        been modified and reload the changed configuration.

      + The GNU C Library now supports an arbitrary number of search
        domains (configured using the “search” directive in
        /etc/resolv.conf).

      + When the “rotate” (RES_ROTATE) resolver option is active, the
        GNU C Library will now randomly pick a name server from the
        configuration as a starting point.

    * The tunables feature is now enabled by default.  This allows
      users to tweak behaviour of the GNU C Library using the
      GLIBC_TUNABLES environment variable.

    * New function reallocarray, which resizes an allocated block
      (like realloc) to the product of two sizes, with a guaranteed
      clean failure upon integer overflow in the multiplication.

    * New wrappers for the Linux-specific system calls preadv2 and
      pwritev2.  These are extended versions of preadv and pwritev,
      respectively, taking an additional flags argument.  The set of
      supported flags depends on the running kernel; full support
      currently requires kernel 4.7 or later.

    * posix_spawnattr_setflags now supports the flag
      POSIX_SPAWN_SETSID, to create a new session ID for the spawned
      process.

    * errno.h is now safe to use from C-preprocessed assembly language
      on all supported operating systems.  In this context, it will
      only define the Exxxx constants, as preprocessor macros
      expanding to integer literals.

    * On ia64, powerpc64le, x86-32, and x86-64, the math library now
      implements 128-bit floating point as defined by ISO/IEC/IEEE
      60559:2011 (IEEE 754-2008) and ISO/IEC TS 18661-3:2015.

That's it for this time.  More in the fall...

Cheers
  Nick


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