Introduce strub: machine-independent stack scrubbing

This patch adds the strub attribute for function and variable types,
command-line options, passes and adjustments to implement it,
documentation, and tests.

Stack scrubbing is implemented in a machine-independent way: functions
with strub enabled are modified so that they take an extra stack
watermark argument, that they update with their stack use, and the
caller can then zero it out once it regains control, whether by return
or exception.  There are two ways to go about it: at-calls, that
modifies the visible interface (signature) of the function, and
internal, in which the body is moved to a clone, the clone undergoes
the interface change, and the function becomes a wrapper, preserving
its original interface, that calls the clone and then clears the stack
used by it.

Variables can also be annotated with the strub attribute, so that
functions that read from them get stack scrubbing enabled implicitly,
whether at-calls, for functions only usable within a translation unit,
or internal, for functions whose interfaces must not be modified.

There is a strict mode, in which functions that have their stack
scrubbed can only call other functions with stack-scrubbing
interfaces, or those explicitly marked as callable from strub
contexts, so that an entire call chain gets scrubbing, at once or
piecemeal depending on optimization levels.  In the default mode,
relaxed, this requirement is not enforced by the compiler.

The implementation adds two IPA passes, one that assigns strub modes
early on, another that modifies interfaces and adds calls to the
builtins that jointly implement stack scrubbing.  Another builtin,
that obtains the stack pointer, is added for use in the implementation
of the builtins, whether expanded inline or called in libgcc.

There are new command-line options to change operation modes and to
force the feature disabled; it is enabled by default, but it has no
effect and is implicitly disabled if the strub attribute is never
used.  There are also options meant to use for testing the feature,
enabling different strubbing modes for all (viable) functions.


for  gcc/ChangeLog

	* Makefile.in (OBJS): Add ipa-strub.o.
	(GTFILES): Add ipa-strub.cc.
	* builtins.def (BUILT_IN_STACK_ADDRESS): New.
	(BUILT_IN___STRUB_ENTER): New.
	(BUILT_IN___STRUB_UPDATE): New.
	(BUILT_IN___STRUB_LEAVE): New.
	* builtins.cc: Include ipa-strub.h.
	(STACK_STOPS, STACK_UNSIGNED): Define.
	(expand_builtin_stack_address): New.
	(expand_builtin_strub_enter): New.
	(expand_builtin_strub_update): New.
	(expand_builtin_strub_leave): New.
	(expand_builtin): Call them.
	* common.opt (fstrub=*): New options.
	* doc/extend.texi (strub): New type attribute.
	(__builtin_stack_address): New function.
	(Stack Scrubbing): New section.
	* doc/invoke.texi (-fstrub=*): New options.
	(-fdump-ipa-*): New passes.
	* gengtype-lex.l: Ignore multi-line pp-directives.
	* ipa-inline.cc: Include ipa-strub.h.
	(can_inline_edge_p): Test strub_inlinable_to_p.
	* ipa-split.cc: Include ipa-strub.h.
	(execute_split_functions): Test strub_splittable_p.
	* ipa-strub.cc, ipa-strub.h: New.
	* passes.def: Add strub_mode and strub passes.
	* tree-cfg.cc (gimple_verify_flow_info): Note on debug stmts.
	* tree-pass.h (make_pass_ipa_strub_mode): Declare.
	(make_pass_ipa_strub): Declare.
	(make_pass_ipa_function_and_variable_visibility): Fix
	formatting.
	* tree-ssa-ccp.cc (optimize_stack_restore): Keep restores
	before strub leave.
	* attribs.cc: Include ipa-strub.h.
	(decl_attributes): Support applying attributes to function
	type, rather than pointer type, at handler's request.
	(comp_type_attributes): Combine strub_comptypes and target
	comp_type results.
	* doc/tm.texi.in (TARGET_STRUB_USE_DYNAMIC_ARRAY): New.
	(TARGET_STRUB_MAY_USE_MEMSET): New.
	* doc/tm.texi: Rebuilt.
	* cgraph.h (symtab_node::reset): Add preserve_comdat_group
	param, with a default.
	* cgraphunit.cc (symtab_node::reset): Use it.

for  gcc/c-family/ChangeLog

	* c-attribs.cc: Include ipa-strub.h.
	(handle_strub_attribute): New.
	(c_common_attribute_table): Add strub.

for  gcc/ada/ChangeLog

	* gcc-interface/trans.cc: Include ipa-strub.h.
	(gigi): Make internal decls for targets of compiler-generated
	calls strub-callable too.
	(build_raise_check): Likewise.
	* gcc-interface/utils.cc: Include ipa-strub.h.
	(handle_strub_attribute): New.
	(gnat_internal_attribute_table): Add strub.

for  gcc/testsuite/ChangeLog

	* c-c++-common/strub-O0.c: New.
	* c-c++-common/strub-O1.c: New.
	* c-c++-common/strub-O2.c: New.
	* c-c++-common/strub-O2fni.c: New.
	* c-c++-common/strub-O3.c: New.
	* c-c++-common/strub-O3fni.c: New.
	* c-c++-common/strub-Og.c: New.
	* c-c++-common/strub-Os.c: New.
	* c-c++-common/strub-all1.c: New.
	* c-c++-common/strub-all2.c: New.
	* c-c++-common/strub-apply1.c: New.
	* c-c++-common/strub-apply2.c: New.
	* c-c++-common/strub-apply3.c: New.
	* c-c++-common/strub-apply4.c: New.
	* c-c++-common/strub-at-calls1.c: New.
	* c-c++-common/strub-at-calls2.c: New.
	* c-c++-common/strub-defer-O1.c: New.
	* c-c++-common/strub-defer-O2.c: New.
	* c-c++-common/strub-defer-O3.c: New.
	* c-c++-common/strub-defer-Os.c: New.
	* c-c++-common/strub-internal1.c: New.
	* c-c++-common/strub-internal2.c: New.
	* c-c++-common/strub-parms1.c: New.
	* c-c++-common/strub-parms2.c: New.
	* c-c++-common/strub-parms3.c: New.
	* c-c++-common/strub-relaxed1.c: New.
	* c-c++-common/strub-relaxed2.c: New.
	* c-c++-common/strub-short-O0-exc.c: New.
	* c-c++-common/strub-short-O0.c: New.
	* c-c++-common/strub-short-O1.c: New.
	* c-c++-common/strub-short-O2.c: New.
	* c-c++-common/strub-short-O3.c: New.
	* c-c++-common/strub-short-Os.c: New.
	* c-c++-common/strub-strict1.c: New.
	* c-c++-common/strub-strict2.c: New.
	* c-c++-common/strub-tail-O1.c: New.
	* c-c++-common/strub-tail-O2.c: New.
	* c-c++-common/torture/strub-callable1.c: New.
	* c-c++-common/torture/strub-callable2.c: New.
	* c-c++-common/torture/strub-const1.c: New.
	* c-c++-common/torture/strub-const2.c: New.
	* c-c++-common/torture/strub-const3.c: New.
	* c-c++-common/torture/strub-const4.c: New.
	* c-c++-common/torture/strub-data1.c: New.
	* c-c++-common/torture/strub-data2.c: New.
	* c-c++-common/torture/strub-data3.c: New.
	* c-c++-common/torture/strub-data4.c: New.
	* c-c++-common/torture/strub-data5.c: New.
	* c-c++-common/torture/strub-indcall1.c: New.
	* c-c++-common/torture/strub-indcall2.c: New.
	* c-c++-common/torture/strub-indcall3.c: New.
	* c-c++-common/torture/strub-inlinable1.c: New.
	* c-c++-common/torture/strub-inlinable2.c: New.
	* c-c++-common/torture/strub-ptrfn1.c: New.
	* c-c++-common/torture/strub-ptrfn2.c: New.
	* c-c++-common/torture/strub-ptrfn3.c: New.
	* c-c++-common/torture/strub-ptrfn4.c: New.
	* c-c++-common/torture/strub-pure1.c: New.
	* c-c++-common/torture/strub-pure2.c: New.
	* c-c++-common/torture/strub-pure3.c: New.
	* c-c++-common/torture/strub-pure4.c: New.
	* c-c++-common/torture/strub-run1.c: New.
	* c-c++-common/torture/strub-run2.c: New.
	* c-c++-common/torture/strub-run3.c: New.
	* c-c++-common/torture/strub-run4.c: New.
	* c-c++-common/torture/strub-run4c.c: New.
	* c-c++-common/torture/strub-run4d.c: New.
	* c-c++-common/torture/strub-run4i.c: New.
	* g++.dg/strub-run1.C: New.
	* g++.dg/torture/strub-init1.C: New.
	* g++.dg/torture/strub-init2.C: New.
	* g++.dg/torture/strub-init3.C: New.
	* gnat.dg/strub_attr.adb, gnat.dg/strub_attr.ads: New.
	* gnat.dg/strub_ind.adb, gnat.dg/strub_ind.ads: New.

for  libgcc/ChangeLog

	* Makefile.in (LIB2ADD): Add strub.c.
	* libgcc2.h (__strub_enter, __strub_update, __strub_leave):
	Declare.
	* strub.c: New.
	* libgcc-std.ver.in (__strub_enter): Add to GCC_14.0.0.
	(__strub_update, __strub_leave): Likewise.

1 files changed, 19 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 2b4d283..ebc1d3d 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -2686,6 +2686,25 @@ in DWARF 2 debug information.  The default is zero.  A different value
 may reduce the size of debug information on some ports.
 @end defmac
 
+@defmac TARGET_STRUB_USE_DYNAMIC_ARRAY
+If defined to nonzero, @code{__strub_leave} will allocate a dynamic
+array covering the stack range that needs scrubbing before clearing it.
+Allocating the array tends to make scrubbing slower, but it enables the
+scrubbing to be safely implemented with a @code{memset} call, which
+could make up for the difference.
+@end defmac
+
+@defmac TARGET_STRUB_MAY_USE_MEMSET
+If defined to nonzero, enable @code{__strub_leave} to be optimized so as
+to call @code{memset} for stack scrubbing.  This is only enabled by
+default if @code{TARGET_STRUB_USE_DYNAMIC_ARRAY} is enabled; it's not
+advisable to enable it otherwise, since @code{memset} would then likely
+overwrite its own stack frame, but it might work if the target ABI
+enables @code{memset} to not use the stack at all, not even for
+arguments or its return address, and its implementation is trivial
+enough that it doesn't use a stack frame.
+@end defmac
+
 @node Exception Handling
 @subsection Exception Handling Support
 @cindex exception handling