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October/November GNU Toolchain Update


Hi Guys,

  Sorry for the delay between these updates.  My new job is keeping
  me very busy...  Anyway here are the highlights of the changes in
  the GNU toolchain over the last two months:


  The compiler and assembler now have support for the ARC EM/HS and
  ARC600/700 architectures and the Power9 variant of the PowerPC
  architecture.  


  The GCC mainline sources are now in Stage 3 (bug fixes only) which
  means that a branch may be happening soon.


  The Binutils sources have branched, getting ready for a 2.26 release
  soon.


  GDB's record instruction-history command accepts a new modifier: /s.
  This behaves exactly like the /m modifier and prints mixed source +
  disassembly into the history.


  GDB now supports displaced stepping on AArch64 GNU/Linux.


  GCC's named address space feature has been extended to add address
  spaces for the x86 architecture.  Here variables may be declared as
  being relative to the %fs or %gs segments using the __seg_fs and
  __seg_gs attributes.  Alternatively if one of these segments is used
  for thread local storage then the __seg_tls attribute can be used
  access the correct segment.


  GCC's function attribute feature has been extended to support
  another attribute:
  
    target_clones (<options>)

  This is used to specify that a function is to be cloned into
  multiple versions compiled with different target options than
  specified on the command line.  The supported options and
  restrictions are the same as for target attribute.

  For instance on an x86, you could compile a function with
  target_clones("sse4.1,avx").   It will create 2 function clones,
  one compiled with -msse4.1 and another with -mavx.  At the function
  call it will create resolver ifunc, that will dynamically call a
  clone suitable for current architecture.


  A new type attribute has been added to specify the endianness of the
  fields in a struct, union or array:

    scalar_storage_order ("<endianness>")
    
  This attribute sets the storage order, aka endianness, of the scalar
  fields of the type to either "big-endian" or "little-endian".  The
  attribute has no effects on fields which are themselves a union, a
  struct or an array whose component is a union or a struct, and it is
  possible to have fields with a different scalar storage order than
  the enclosing type.

  Additional restrictions are enforced for types with the reverse
  scalar storage order with regard to the scalar storage order of the
  target: 

    * Taking the address of a scalar field of a union or a struct with
      reverse scalar storage order is not permitted and will yield an
      error.
    
    * Taking the address of an array field, whose component is scalar,
      of a union or a struct with reverse scalar storage order is
      permitted but will yield a warning, unless the option
      -Wno-scalar-storage-order is specified.

    * Taking the address of a union or a struct with reverse scalar
    storage order is permitted. 

  These restrictions exist because the storage order attribute is lost
  when the address of a scalar or the address of an array with scalar
  component is taken, so storing indirectly through this address will
  generally not work.  The second case is nevertheless allowed to be
  able to perform a block copy from or to the array.


  A new warning option: -Wduplicated-cond will produce messages
  whenever a condition is duplicated in an if-else-if chain.  For
  example:
  
    if (p->q != NULL) { ... }
    else if (p->q != NULL) { ... }


  A new option: -fkeep-static-functions will make sure that gcc will
  generate code for static functions that are never used.


  The block reordering optimization in gcc can now be tuned via the
  option: -freorder-blocks-algorithm=<simple|stc>.  The default for
  optimization levels below -O2 (or at -Os) is the "simple" algorithm 
  which does not increase code size.  The new "stc" algorithm stands
  for "software trace cache" and it tries to put all often executed
  code together, minimizing the number of branches executed by
  making extra copies of code.


  The ARM backend supports a new option: -mlow-precision-recip-sqrt
  which uses two steps instead of three for double-precision
  reciprocal square root calculations.  (It also uses one step instead
  of two steps for single-precision calculations).  This reduces the
  latency and precision of the operation.


  The x86 and x86_64 backends support a new option: -mms-bitfields
  This enables a bit-field layout compatible with the native Microsoft
  Windows compiler.   This option is enabled by default for Windows
  targets.
  

  The x86 and x86_64 backends also support the new option:
  
    -mmitigate-rop

  This tries to avoid generating code sequences that contain
  unintended return opcodes, to mitigate against certain forms of
  attack.  At the moment, this option is limited in what it can do and
  should not be relied on to provide serious protection.


  The assembler and linker now support a configure time option to
  enable the automatic compression of debug sections.  This is off by
  default, but after the next release of the binutils, it will be
  switched on by default for some targets.


  The linker supports a new ARM specific command line option:
  --fix-stm32l4xx-629360.  This enables a link-time workaround for a
  bug in the bus matrix / memory controller for some of the STM32
  Cortex-M4 based products (STM32L4xx).


  The objcopy program now has the ability to insert new symbols into
  an object file or executable.  It is controlled by the option:
  
    --add-symbol <name>=[<section>:]<value>[,<flags>]
    
  This adds a new symbol called <name>.  If the <section> is given,
  the symbol will be associated with and relative to that section,
  otherwise it will be an absolute symbol.  Symbol flags can be
  specified as well although not all flags will be meaningful for all
  object file formats.  The special flag 'before=<othersym>' will
  insert the new symbol in front of the specified <othersym>,
  otherwise the symbol(s) will be added at the end of the symbol table
  in the order they appear. 


  The MSP430 port of gas accepts a new command line option to control
  workarounds for various silicon errata:
  
    -msilicon-errata=<name>[,<name>...]

  This option enables the specified workarounds, but does not produce
  any informative output for the user when it does so.  The related
  option:

    -msilicon-errata-warn=<name>[,<name>...]

  can be used to produce warning messages whenever a situation where a 
  silicon errata might be valid is encountered by the assembler.


  The x86/x86_64 linkers now support a command line option to specify
  the byte to be used as padding when transforming an indirect call to
  a locally defined function 'foo' into a call via its GOT slot:

   -z call-nop=prefix-addr    generates: "0x67 call foo"
   -z call-nop=prefix-nop     generates: "0x90 call foo"
   -z call-nop=suffix-nop     generates: "call foo 0x90"
   -z call-nop=prefix-<byte>  generates: "<byte> call foo"
   -z call-nop=suffix-<byte>  generates: "call foo <byte>"


Lastly, here are the monthly DG test results for the various toolchains
that I am able to simulate on my local machine:

                          GCC/DG unexpected failures
                        ------------------------------
                        Aug'15  Sep'15  Oct'15  Nov'15
aarch64-elf                -       -       -     549
arm-eabi                   4       4      40      42
bfin-elf                  11      12      47      50
frv-elf                  541      24      60      63
h8300-elf                 71      71     110     120
iq2000-elf               684     687     728     736
m32r-elf                   -       9      45      48
mcore-elf                519     517     557     565
mipsisa32-elf             25      24      67      69
mipsisa64-elf             26      25      68      70
mn10300-elf              468      12      47      50
msp430-elf               100     559     101     133
powerpc-eabispe           15      15      51      54
rl78-elf                  99      99     139     148
rx-elf                    42      41      77      87
sh-elf                     6       6      42      45
v850e-elf                 31      31      67      70
x86_64-pc-linux-gnu        2       2      39      38

                          G++/DG unexpected failures
                        ------------------------------
                        Aug'15  Sep'15  Oct'15  Nov'15
aarch64-elf                -       -       -    2110      
arm-eabi                  35      35     146     153
bfin-elf                  23      23     134     134
frv-elf                    -     124     226     230
h8300-elf                294     297     414     519
iq2000-elf              3296    3336    3154     449
m32r-elf                   -     102     213      48
mcore-elf               2221    2222    3160    2341
mipsisa32-elf            926     923    2099    1039
mipsisa64-elf            926     926    1037    1042
mn10300-elf                -      74     188     187
msp430-elf              1050    2449    1164    1178
powerpc-eabispe          135     150     136     136
rl78-elf                   -     884     884	1191
rx-elf                    50      50     158     173
sh-elf                    35      35     146     149
v850e-elf                  -      94     247     247
x86_64-pc-linux-gnu       17      17     125      38


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