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, 18 insertions, 0 deletions

diff --git a/gcc/ada/gcc-interface/trans.cc b/gcc/ada/gcc-interface/trans.cc
index 9c418be..5e9e92d 100644
--- a/gcc/ada/gcc-interface/trans.cc
+++ b/gcc/ada/gcc-interface/trans.cc
@@ -69,6 +69,21 @@
 #include "ada-tree.h"
 #include "gigi.h"
 
+/* The following #include is for strub_make_callable.
+
+   This function marks a function as safe to call from strub contexts.  We mark
+   Ada subprograms that may be called implicitly by the compiler, and that won't
+   leave on the stack caller data passed to them.  This stops implicit calls
+   introduced in subprograms that have their stack scrubbed from being flagged
+   as unsafe, even in -fstrub=strict mode.
+
+   These subprograms are also marked with the strub(callable) attribute in Ada
+   sources, but their declarations aren't necessarily imported by GNAT, or made
+   visible to gigi, in units that end up relying on them.  So when gigi
+   introduces their declarations on its own, it must also add the attribute, by
+   calling strub_make_callable.  */
+#include "ipa-strub.h"
+
 /* We should avoid allocating more than ALLOCA_THRESHOLD bytes via alloca,
    for fear of running out of stack space.  If we need more, we use xmalloc
    instead.  */
@@ -454,6 +469,7 @@ gigi (Node_Id gnat_root,
 						     int64_type, NULL_TREE),
 			   NULL_TREE, is_default, true, true, true, false,
 			   false, NULL, Empty);
+  strub_make_callable (mulv64_decl);
 
   if (Enable_128bit_Types)
     {
@@ -466,6 +482,7 @@ gigi (Node_Id gnat_root,
 							 NULL_TREE),
 			       NULL_TREE, is_default, true, true, true, false,
 			       false, NULL, Empty);
+      strub_make_callable (mulv128_decl);
     }
 
   /* Name of the _Parent field in tagged record types.  */
@@ -722,6 +739,7 @@ build_raise_check (int check, enum exception_info_kind kind)
     = create_subprog_decl (get_identifier (Name_Buffer), NULL_TREE, ftype,
 			   NULL_TREE, is_default, true, true, true, false,
 			   false, NULL, Empty);
+  strub_make_callable (result);
   set_call_expr_flags (result, ECF_NORETURN | ECF_XTHROW);
 
   return result;