On Tue, Aug 8, 2017 at 6:54 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> 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.

Attached addition adds -mstack-protector-guard-symbol= option that
overrides the offset to TLS stack protector canary with a symbol name.
Using this option, stack protector canary can be loaded from specified
symbol, relative to guard reg:

gcc -O2 -fstack-protector-all -mstack-protector-guard=tls
-mstack-protector-guard-reg=gs -mstack-protector-guard-symbol=my_guard

        movq    %gs:my_guard(%rip), %rax
        movq    %rax, 8(%rsp)
        xorl    %eax, %eax
        movq    8(%rsp), %rax
        xorq    %gs:my_guard(%rip), %rax

2017-08-09  Uros Bizjak  <ubizjak@gmail.com>

    PR target/81708
    * config/i386/i386.opt (mstack-protector-guard-symbol=): New option
    * config/i386/i386.c (ix86_stack_protect_guard): Use
    ix86_stack_protect_guard_symbol_str to generate varible declaration.
    * doc/invoke.texi (x86 Options): Document
    -mstack-protector-guard-symbol= option.

testsuite/ChangeLog:

2017-08-09  Uros Bizjak  <ubizjak@gmail.com>

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

Patch was bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

I plan to commit the patch to mainline SVN in a couple of days.

Uros.