-mstack-protector-guard and friends (PR78875)

-mstack-protector-guard and friends (PR78875)

Currently, on PowerPC, code compiled with -fstack-protector will load
the canary from -0x7010(13) (for -m64) or from -0x7008(2) (for -m32)
if GCC was compiled against GNU libc 2.4 or newer or some other libc
that supports -fstack-protector, and from the global variable
__stack_chk_guard otherwise.

This does not work well for Linux and other OS kernels and similar.
For such non-standard applications, this patch creates a few new
command-line options.  The relevant new use cases are:

-mstack-protector-guard=global
Use the __stack_chk_guard variable, no matter how this GCC was
configured.

-mstack-protector-guard=tls
Use the canary from TLS.  This will error out if this GCC was built
with a C library that does not support it.

-mstack-protector-guard=tls -mstack-protector-register=<reg>
-mstack-protector-offset=<offset>
Load the canary from offset <off> from base register <reg>.

	PR target/78875
	* config/rs6000/rs6000-opts.h (stack_protector_guard): New enum.
	* config/rs6000/rs6000.c (rs6000_option_override_internal): Handle
	the new options.
	* config/rs6000/rs6000.md (stack_protect_set): Handle the new more
	flexible settings.
	(stack_protect_test): Ditto.
	* config/rs6000/rs6000.opt (mstack-protector-guard=,
	mstack-protector-guard-reg=, mstack-protector-guard-offset=): New
	options.
	* doc/invoke.texi (Option Summary) [RS/6000 and PowerPC Options]:
	Add -mstack-protector-guard=, -mstack-protector-guard-reg=, and
	-mstack-protector-guard-offset=.
	(RS/6000 and PowerPC Options): Ditto.

gcc/testsuite/
	* gcc.target/powerpc/ssp-1.c: New testcase.
	* gcc.target/powerpc/ssp-2.c: New testcase.

From-SVN: r244556