Hello!

Attached patch introduces -mstack-protector-guard-reg=  and
-mstack-protector-guard-offset= options to make stack canary location
customizable. These are the same options powerpc has.

2017-08-08  Uros Bizjak  <ubizjak@gmail.com>

    PR target/81708
    * config/i386/i386.opt (mstack-protector-guard-reg=): New option
    (mstack-protector-guard-offset=): Ditto.
    * config/i386/i386.c (ix86_option_override): Handle
    -mstack-protector-guard-reg= and -mstack-protector-guard-offset=
    options.
    (ix86_stack_protect_guard): Use ix86_stack_protect_guard_reg and
    ix86_stack_protect_guard_offset variables.
    (TARGET_STACK_PROTECT_GUARD): Always define.
    * doc/invoke.texi (x86 Options): Document -mstack-protector-guard-reg=
    and -mstack-protector-guard-offset= options.

testsuite/ChangeLog:

2017-08-08  Uros Bizjak  <ubizjak@gmail.com>

    PR target/81708
    * gcc.target/i386/stack-prot-guard.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Committed to mainline SVN. I will mention new options in gcc-8 changes
webpage later.

Uros.